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  • If I never ever use HashSet, should I still implement GetHashCode?

    - by Dimitri C.
    I never need to store objects in a hash table. The reason is twofold: coming up with a good hash function is difficult and error prone. an AVL tree is almost always fast enough, and it merely requires a strict order predicate, which is much easier to implement. The Equals() operation on the other hand is a very frequently used function. Therefore I wonder whether it is necessary to implement GetHashCode (which I never need) when implementing the Equals function (which I often need)?

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  • C#/.NET Little Wonders: The Joy of Anonymous Types

    - by James Michael Hare
    Once again, in this series of posts I look at the parts of the .NET Framework that may seem trivial, but can help improve your code by making it easier to write and maintain. The index of all my past little wonders posts can be found here. In the .NET 3 Framework, Microsoft introduced the concept of anonymous types, which provide a way to create a quick, compiler-generated types at the point of instantiation.  These may seem trivial, but are very handy for concisely creating lightweight, strongly-typed objects containing only read-only properties that can be used within a given scope. Creating an Anonymous Type In short, an anonymous type is a reference type that derives directly from object and is defined by its set of properties base on their names, number, types, and order given at initialization.  In addition to just holding these properties, it is also given appropriate overridden implementations for Equals() and GetHashCode() that take into account all of the properties to correctly perform property comparisons and hashing.  Also overridden is an implementation of ToString() which makes it easy to display the contents of an anonymous type instance in a fairly concise manner. To construct an anonymous type instance, you use basically the same initialization syntax as with a regular type.  So, for example, if we wanted to create an anonymous type to represent a particular point, we could do this: 1: var point = new { X = 13, Y = 7 }; Note the similarity between anonymous type initialization and regular initialization.  The main difference is that the compiler generates the type name and the properties (as readonly) based on the names and order provided, and inferring their types from the expressions they are assigned to. It is key to remember that all of those factors (number, names, types, order of properties) determine the anonymous type.  This is important, because while these two instances share the same anonymous type: 1: // same names, types, and order 2: var point1 = new { X = 13, Y = 7 }; 3: var point2 = new { X = 5, Y = 0 }; These similar ones do not: 1: var point3 = new { Y = 3, X = 5 }; // different order 2: var point4 = new { X = 3, Y = 5.0 }; // different type for Y 3: var point5 = new {MyX = 3, MyY = 5 }; // different names 4: var point6 = new { X = 1, Y = 2, Z = 3 }; // different count Limitations on Property Initialization Expressions The expression for a property in an anonymous type initialization cannot be null (though it can evaluate to null) or an anonymous function.  For example, the following are illegal: 1: // Null can't be used directly. Null reference of what type? 2: var cantUseNull = new { Value = null }; 3:  4: // Anonymous methods cannot be used. 5: var cantUseAnonymousFxn = new { Value = () => Console.WriteLine(“Can’t.”) }; Note that the restriction on null is just that you can’t use it directly as the expression, because otherwise how would it be able to determine the type?  You can, however, use it indirectly assigning a null expression such as a typed variable with the value null, or by casting null to a specific type: 1: string str = null; 2: var fineIndirectly = new { Value = str }; 3: var fineCast = new { Value = (string)null }; All of the examples above name the properties explicitly, but you can also implicitly name properties if they are being set from a property, field, or variable.  In these cases, when a field, property, or variable is used alone, and you don’t specify a property name assigned to it, the new property will have the same name.  For example: 1: int variable = 42; 2:  3: // creates two properties named varriable and Now 4: var implicitProperties = new { variable, DateTime.Now }; Is the same type as: 1: var explicitProperties = new { variable = variable, Now = DateTime.Now }; But this only works if you are using an existing field, variable, or property directly as the expression.  If you use a more complex expression then the name cannot be inferred: 1: // can't infer the name variable from variable * 2, must name explicitly 2: var wontWork = new { variable * 2, DateTime.Now }; In the example above, since we typed variable * 2, it is no longer just a variable and thus we would have to assign the property a name explicitly. ToString() on Anonymous Types One of the more trivial overrides that an anonymous type provides you is a ToString() method that prints the value of the anonymous type instance in much the same format as it was initialized (except actual values instead of expressions as appropriate of course). For example, if you had: 1: var point = new { X = 13, Y = 42 }; And then print it out: 1: Console.WriteLine(point.ToString()); You will get: 1: { X = 13, Y = 42 } While this isn’t necessarily the most stunning feature of anonymous types, it can be handy for debugging or logging values in a fairly easy to read format. Comparing Anonymous Type Instances Because anonymous types automatically create appropriate overrides of Equals() and GetHashCode() based on the underlying properties, we can reliably compare two instances or get hash codes.  For example, if we had the following 3 points: 1: var point1 = new { X = 1, Y = 2 }; 2: var point2 = new { X = 1, Y = 2 }; 3: var point3 = new { Y = 2, X = 1 }; If we compare point1 and point2 we’ll see that Equals() returns true because they overridden version of Equals() sees that the types are the same (same number, names, types, and order of properties) and that the values are the same.   In addition, because all equal objects should have the same hash code, we’ll see that the hash codes evaluate to the same as well: 1: // true, same type, same values 2: Console.WriteLine(point1.Equals(point2)); 3:  4: // true, equal anonymous type instances always have same hash code 5: Console.WriteLine(point1.GetHashCode() == point2.GetHashCode()); However, if we compare point2 and point3 we get false.  Even though the names, types, and values of the properties are the same, the order is not, thus they are two different types and cannot be compared (and thus return false).  And, since they are not equal objects (even though they have the same value) there is a good chance their hash codes are different as well (though not guaranteed): 1: // false, different types 2: Console.WriteLine(point2.Equals(point3)); 3:  4: // quite possibly false (was false on my machine) 5: Console.WriteLine(point2.GetHashCode() == point3.GetHashCode()); Using Anonymous Types Now that we’ve created instances of anonymous types, let’s actually use them.  The property names (whether implicit or explicit) are used to access the individual properties of the anonymous type.  The main thing, once again, to keep in mind is that the properties are readonly, so you cannot assign the properties a new value (note: this does not mean that instances referred to by a property are immutable – for more information check out C#/.NET Fundamentals: Returning Data Immutably in a Mutable World). Thus, if we have the following anonymous type instance: 1: var point = new { X = 13, Y = 42 }; We can get the properties as you’d expect: 1: Console.WriteLine(“The point is: ({0},{1})”, point.X, point.Y); But we cannot alter the property values: 1: // compiler error, properties are readonly 2: point.X = 99; Further, since the anonymous type name is only known by the compiler, there is no easy way to pass anonymous type instances outside of a given scope.  The only real choices are to pass them as object or dynamic.  But really that is not the intention of using anonymous types.  If you find yourself needing to pass an anonymous type outside of a given scope, you should really consider making a POCO (Plain Old CLR Type – i.e. a class that contains just properties to hold data with little/no business logic) instead. Given that, why use them at all?  Couldn’t you always just create a POCO to represent every anonymous type you needed?  Sure you could, but then you might litter your solution with many small POCO classes that have very localized uses. It turns out this is the key to when to use anonymous types to your advantage: when you just need a lightweight type in a local context to store intermediate results, consider an anonymous type – but when that result is more long-lived and used outside of the current scope, consider a POCO instead. So what do we mean by intermediate results in a local context?  Well, a classic example would be filtering down results from a LINQ expression.  For example, let’s say we had a List<Transaction>, where Transaction is defined something like: 1: public class Transaction 2: { 3: public string UserId { get; set; } 4: public DateTime At { get; set; } 5: public decimal Amount { get; set; } 6: // … 7: } And let’s say we had this data in our List<Transaction>: 1: var transactions = new List<Transaction> 2: { 3: new Transaction { UserId = "Jim", At = DateTime.Now, Amount = 2200.00m }, 4: new Transaction { UserId = "Jim", At = DateTime.Now, Amount = -1100.00m }, 5: new Transaction { UserId = "Jim", At = DateTime.Now.AddDays(-1), Amount = 900.00m }, 6: new Transaction { UserId = "John", At = DateTime.Now.AddDays(-2), Amount = 300.00m }, 7: new Transaction { UserId = "John", At = DateTime.Now, Amount = -10.00m }, 8: new Transaction { UserId = "Jane", At = DateTime.Now, Amount = 200.00m }, 9: new Transaction { UserId = "Jane", At = DateTime.Now, Amount = -50.00m }, 10: new Transaction { UserId = "Jaime", At = DateTime.Now.AddDays(-3), Amount = -100.00m }, 11: new Transaction { UserId = "Jaime", At = DateTime.Now.AddDays(-3), Amount = 300.00m }, 12: }; So let’s say we wanted to get the transactions for each day for each user.  That is, for each day we’d want to see the transactions each user performed.  We could do this very simply with a nice LINQ expression, without the need of creating any POCOs: 1: // group the transactions based on an anonymous type with properties UserId and Date: 2: byUserAndDay = transactions 3: .GroupBy(tx => new { tx.UserId, tx.At.Date }) 4: .OrderBy(grp => grp.Key.Date) 5: .ThenBy(grp => grp.Key.UserId); Now, those of you who have attempted to use custom classes as a grouping type before (such as GroupBy(), Distinct(), etc.) may have discovered the hard way that LINQ gets a lot of its speed by utilizing not on Equals(), but also GetHashCode() on the type you are grouping by.  Thus, when you use custom types for these purposes, you generally end up having to write custom Equals() and GetHashCode() implementations or you won’t get the results you were expecting (the default implementations of Equals() and GetHashCode() are reference equality and reference identity based respectively). As we said before, it turns out that anonymous types already do these critical overrides for you.  This makes them even more convenient to use!  Instead of creating a small POCO to handle this grouping, and then having to implement a custom Equals() and GetHashCode() every time, we can just take advantage of the fact that anonymous types automatically override these methods with appropriate implementations that take into account the values of all of the properties. Now, we can look at our results: 1: foreach (var group in byUserAndDay) 2: { 3: // the group’s Key is an instance of our anonymous type 4: Console.WriteLine("{0} on {1:MM/dd/yyyy} did:", group.Key.UserId, group.Key.Date); 5:  6: // each grouping contains a sequence of the items. 7: foreach (var tx in group) 8: { 9: Console.WriteLine("\t{0}", tx.Amount); 10: } 11: } And see: 1: Jaime on 06/18/2012 did: 2: -100.00 3: 300.00 4:  5: John on 06/19/2012 did: 6: 300.00 7:  8: Jim on 06/20/2012 did: 9: 900.00 10:  11: Jane on 06/21/2012 did: 12: 200.00 13: -50.00 14:  15: Jim on 06/21/2012 did: 16: 2200.00 17: -1100.00 18:  19: John on 06/21/2012 did: 20: -10.00 Again, sure we could have just built a POCO to do this, given it an appropriate Equals() and GetHashCode() method, but that would have bloated our code with so many extra lines and been more difficult to maintain if the properties change.  Summary Anonymous types are one of those Little Wonders of the .NET language that are perfect at exactly that time when you need a temporary type to hold a set of properties together for an intermediate result.  While they are not very useful beyond the scope in which they are defined, they are excellent in LINQ expressions as a way to create and us intermediary values for further expressions and analysis. Anonymous types are defined by the compiler based on the number, type, names, and order of properties created, and they automatically implement appropriate Equals() and GetHashCode() overrides (as well as ToString()) which makes them ideal for LINQ expressions where you need to create a set of properties to group, evaluate, etc. Technorati Tags: C#,CSharp,.NET,Little Wonders,Anonymous Types,LINQ

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  • C# WCF Server retrieves 'List<T>' with 1 entry, but client doesn't receive it?! Please help Urgentl

    - by Neville
    Hi Everyone, I've been battling and trying to research this issue for over 2 days now with absolutely no luck. I am trying to retrieve a list of clients from the server (server using fluentNHibernate). The client object is as follow: [DataContract] //[KnownType(typeof(System.Collections.Generic.List<ContactPerson>))] //[KnownType(typeof(System.Collections.Generic.List<Address>))] //[KnownType(typeof(System.Collections.Generic.List<BatchRequest>))] //[KnownType(typeof(System.Collections.Generic.List<Discount>))] [KnownType(typeof(EClientType))] [KnownType(typeof(EComType))] public class Client { #region Properties [DataMember] public virtual int ClientID { get; set; } [DataMember] public virtual EClientType ClientType { get; set; } [DataMember] public virtual string RegisterID {get; set;} [DataMember] public virtual string HerdCode { get; set; } [DataMember] public virtual string CompanyName { get; set; } [DataMember] public virtual bool InvoicePerBatch { get; set; } [DataMember] public virtual EComType ResultsComType { get; set; } [DataMember] public virtual EComType InvoiceComType { get; set; } //[DataMember] //public virtual IList<ContactPerson> Contacts { get; set; } //[DataMember] //public virtual IList<Address> Addresses { get; set; } //[DataMember] //public virtual IList<BatchRequest> Batches { get; set; } //[DataMember] //public virtual IList<Discount> Discounts { get; set; } #endregion #region Overrides public override bool Equals(object obj) { var other = obj as Client; if (other == null) return false; return other.GetHashCode() == this.GetHashCode(); } public override int GetHashCode() { return ClientID.GetHashCode() | ClientType.GetHashCode() | RegisterID.GetHashCode() | HerdCode.GetHashCode() | CompanyName.GetHashCode() | InvoicePerBatch.GetHashCode() | ResultsComType.GetHashCode() | InvoiceComType.GetHashCode();// | Contacts.GetHashCode() | //Addresses.GetHashCode() | Batches.GetHashCode() | Discounts.GetHashCode(); } #endregion } As you can see, I have allready tried to remove the sub-lists, though even with this simplified version of the client I still run into the propblem. my fluent mapping is: public class ClientMap : ClassMap<Client> { public ClientMap() { Table("Clients"); Id(p => p.ClientID); Map(p => p.ClientType).CustomType<EClientType>(); ; Map(p => p.RegisterID); Map(p => p.HerdCode); Map(p => p.CompanyName); Map(p => p.InvoicePerBatch); Map(p => p.ResultsComType).CustomType<EComType>(); Map(p => p.InvoiceComType).CustomType<EComType>(); //HasMany<ContactPerson>(p => p.Contacts) // .KeyColumns.Add("ContactPersonID") // .Inverse() // .Cascade.All(); //HasMany<Address>(p => p.Addresses) // .KeyColumns.Add("AddressID") // .Inverse() // .Cascade.All(); //HasMany<BatchRequest>(p => p.Batches) // .KeyColumns.Add("BatchID") // .Inverse() // .Cascade.All(); //HasMany<Discount>(p => p.Discounts) // .KeyColumns.Add("DiscountID") // .Inverse() // .Cascade.All(); } The client method, seen below, connects to the server. The server retrieves the list, and everything looks right in the object, still, when it returns, the client doesn't receive anything (it receive a List object, but with nothing in it. Herewith the calling method: public List<s.Client> GetClientList() { try { s.DataServiceClient svcClient = new s.DataServiceClient(); svcClient.Open(); List<s.Client> clients = new List<s.Client>(); clients = svcClient.GetClientList().ToList<s.Client>(); svcClient.Close(); //when receiving focus from server, the clients object has a count of 0 return clients; } catch (Exception e) { MessageBox.Show(e.Message); } return null; } and the server method: public IList<Client> GetClientList() { var clients = new List<Client>(); try { using (var session = SessionHelper.OpenSession()) { clients = session.Linq<Client>().Where(p => p.ClientID > 0).ToList<Client>(); } } catch (Exception e) { EventLog.WriteEntry("eCOWS.Data", e.Message); } return clients; //returns a list with 1 client in it } the server method interface is: [UseNetDataContractSerializer] [OperationContract] IList<Client> GetClientList(); for final references, here is my client app.config entries: <system.serviceModel> <bindings> <netTcpBinding> <binding name="NetTcpBinding_IDataService" listenBacklog="10" maxConnections="10" transferMode="Buffered" transactionProtocol="OleTransactions" maxReceivedMessageSize="2147483647" maxBufferSize="2147483647" receiveTimeout="00:10:00" sendTimeout="00:10:00"> <readerQuotas maxDepth="51200000" maxStringContentLength="51200000" maxArrayLength="51200000" maxBytesPerRead="51200000" maxNameTableCharCount="51200000" /> <security mode="Transport"/> </binding> </netTcpBinding> </bindings> <client> <endpoint address="net.tcp://localhost:9000/eCOWS/DataService" binding="netTcpBinding" bindingConfiguration="NetTcpBinding_IDataService" contract="eCowsDataService.IDataService" name="NetTcpBinding_IDataService" behaviorConfiguration="eCowsEndpointBehavior"> </endpoint> <endpoint address="MEX" binding="mexHttpBinding" contract="IMetadataExchange" /> </client> <behaviors> <endpointBehaviors> <behavior name="eCowsEndpointBehavior"> <dataContractSerializer maxItemsInObjectGraph="2147483647"/> </behavior> </endpointBehaviors> </behaviors> </system.serviceModel> and my server app.config: <system.serviceModel> <bindings> <netTcpBinding> <binding name="netTcpBinding" maxConnections="10" listenBacklog="10" transferMode="Buffered" transactionProtocol="OleTransactions" maxBufferSize="2147483647" maxReceivedMessageSize="2147483647" sendTimeout="00:10:00" receiveTimeout="00:10:00"> <readerQuotas maxDepth="51200000" maxStringContentLength="51200000" maxArrayLength="51200000" maxBytesPerRead="51200000" maxNameTableCharCount="51200000" /> <security mode="Transport"/> </binding> </netTcpBinding> </bindings> <services> <service name="eCows.Data.Services.DataService" behaviorConfiguration="eCowsServiceBehavior"> <host> <baseAddresses> <add baseAddress="http://localhost:9001/eCOWS/" /> <add baseAddress="net.tcp://localhost:9000/eCOWS/" /> </baseAddresses> </host> <endpoint address="DataService" binding="netTcpBinding" contract="eCows.Data.Services.IDataService" behaviorConfiguration="eCowsEndpointBehaviour"> </endpoint> <endpoint address="MEX" binding="mexHttpBinding" contract="IMetadataExchange" /> </service> </services> <behaviors> <endpointBehaviors> <behavior name="eCowsEndpointBehaviour"> <dataContractSerializer maxItemsInObjectGraph="2147483647" /> </behavior> </endpointBehaviors> <serviceBehaviors> <behavior name="eCowsServiceBehavior"> <serviceMetadata httpGetEnabled="True"/> <serviceThrottling maxConcurrentCalls="10" maxConcurrentSessions="10"/> <serviceDebug includeExceptionDetailInFaults="False" /> </behavior> <behavior name="MexBehaviour"> <serviceMetadata /> </behavior> </serviceBehaviors> </behaviors> </system.serviceModel> I use to run into "socket closed / network or timeout" errors, and the trace showed clearly that on the callback it was looking for a listening endpoint, but couldn't find one. Anyway, after adding the UseNetSerializer that error went away, yet now I'm just not getting anything. Oh PS. if I add all the commented out List items, I still retrieve an entry from the DB, but also still not receive anything on the client. if I remove the [UseNetDataContractSerializer] I get the following error(s) in the svclog : WARNING: Description Faulted System.ServiceModel.Channels.ServerSessionPreambleConnectionReader+ServerFramingDuplexSessionChannel WARNING: Description Faulted System.ServiceModel.Channels.ServiceChannel ERROR: Initializing[eCows.Data.Models.Client#3]-failed to lazily initialize a collection of role: eCows.Data.Models.Client.Addresses, no session or session was closed ... ERROR: Could not find default endpoint element that references contract 'ILogbookManager' in the ServiceModel client configuration section. This might be because no configuration file was found for your application, or because no endpoint element matching this contract could be found in the client element. If I add a .Not.LazyLoad to the List mapping items, I'm back at not receiving errors, but also not receiving any client information.. Sigh! Please, if anyone can help with this I'd be extremely grateful. I'm probably just missing something small.. but... what is it :) hehe. Thanks in advance! Neville

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  • LINQ – SequenceEqual() method

    - by nmarun
    I have been looking at LINQ extension methods and have blogged about what I learned from them in my blog space. Next in line is the SequenceEqual() method. Here’s the description about this method: “Determines whether two sequences are equal by comparing the elements by using the default equality comparer for their type.” Let’s play with some code: 1: int[] numbers = { 5, 4, 1, 3, 9, 8, 6, 7, 2, 0 }; 2: // int[] numbersCopy = numbers; 3: int[] numbersCopy = { 5, 4, 1, 3, 9, 8, 6, 7, 2, 0 }; 4:  5: Console.WriteLine(numbers.SequenceEqual(numbersCopy)); This gives an output of ‘True’ – basically compares each of the elements in the two arrays and returns true in this case. The result is same even if you uncomment line 2 and comment line 3 (I didn’t need to say that now did I?). So then what happens for custom types? For this, I created a Product class with the following definition: 1: class Product 2: { 3: public int ProductId { get; set; } 4: public string Name { get; set; } 5: public string Category { get; set; } 6: public DateTime MfgDate { get; set; } 7: public Status Status { get; set; } 8: } 9:  10: public enum Status 11: { 12: Active = 1, 13: InActive = 2, 14: OffShelf = 3, 15: } In my calling code, I’m just adding a few product items: 1: private static List<Product> GetProducts() 2: { 3: return new List<Product> 4: { 5: new Product 6: { 7: ProductId = 1, 8: Name = "Laptop", 9: Category = "Computer", 10: MfgDate = new DateTime(2003, 4, 3), 11: Status = Status.Active, 12: }, 13: new Product 14: { 15: ProductId = 2, 16: Name = "Compact Disc", 17: Category = "Water Sport", 18: MfgDate = new DateTime(2009, 12, 3), 19: Status = Status.InActive, 20: }, 21: new Product 22: { 23: ProductId = 3, 24: Name = "Floppy", 25: Category = "Computer", 26: MfgDate = new DateTime(1993, 3, 7), 27: Status = Status.OffShelf, 28: }, 29: }; 30: } Now for the actual check: 1: List<Product> products1 = GetProducts(); 2: List<Product> products2 = GetProducts(); 3:  4: Console.WriteLine(products1.SequenceEqual(products2)); This one returns ‘False’ and the reason is simple – this one checks for reference equality and the products in the both the lists get different ‘memory addresses’ (sounds like I’m talking in ‘C’). In order to modify this behavior and return a ‘True’ result, we need to modify the Product class as follows: 1: class Product : IEquatable<Product> 2: { 3: public int ProductId { get; set; } 4: public string Name { get; set; } 5: public string Category { get; set; } 6: public DateTime MfgDate { get; set; } 7: public Status Status { get; set; } 8:  9: public override bool Equals(object obj) 10: { 11: return Equals(obj as Product); 12: } 13:  14: public bool Equals(Product other) 15: { 16: //Check whether the compared object is null. 17: if (ReferenceEquals(other, null)) return false; 18:  19: //Check whether the compared object references the same data. 20: if (ReferenceEquals(this, other)) return true; 21:  22: //Check whether the products' properties are equal. 23: return ProductId.Equals(other.ProductId) 24: && Name.Equals(other.Name) 25: && Category.Equals(other.Category) 26: && MfgDate.Equals(other.MfgDate) 27: && Status.Equals(other.Status); 28: } 29:  30: // If Equals() returns true for a pair of objects 31: // then GetHashCode() must return the same value for these objects. 32: // read why in the following articles: 33: // http://geekswithblogs.net/akraus1/archive/2010/02/28/138234.aspx 34: // http://stackoverflow.com/questions/371328/why-is-it-important-to-override-gethashcode-when-equals-method-is-overriden-in-c 35: public override int GetHashCode() 36: { 37: //Get hash code for the ProductId field. 38: int hashProductId = ProductId.GetHashCode(); 39:  40: //Get hash code for the Name field if it is not null. 41: int hashName = Name == null ? 0 : Name.GetHashCode(); 42:  43: //Get hash code for the ProductId field. 44: int hashCategory = Category.GetHashCode(); 45:  46: //Get hash code for the ProductId field. 47: int hashMfgDate = MfgDate.GetHashCode(); 48:  49: //Get hash code for the ProductId field. 50: int hashStatus = Status.GetHashCode(); 51: //Calculate the hash code for the product. 52: return hashProductId ^ hashName ^ hashCategory & hashMfgDate & hashStatus; 53: } 54:  55: public static bool operator ==(Product a, Product b) 56: { 57: // Enable a == b for null references to return the right value 58: if (ReferenceEquals(a, b)) 59: { 60: return true; 61: } 62: // If one is null and the other not. Remember a==null will lead to Stackoverflow! 63: if (ReferenceEquals(a, null)) 64: { 65: return false; 66: } 67: return a.Equals((object)b); 68: } 69:  70: public static bool operator !=(Product a, Product b) 71: { 72: return !(a == b); 73: } 74: } Now THAT kinda looks overwhelming. But lets take one simple step at a time. Ok first thing you’ve noticed is that the class implements IEquatable<Product> interface – the key step towards achieving our goal. This interface provides us with an ‘Equals’ method to perform the test for equality with another Product object, in this case. This method is called in the following situations: when you do a ProductInstance.Equals(AnotherProductInstance) and when you perform actions like Contains<T>, IndexOf() or Remove() on your collection Coming to the Equals method defined line 14 onwards. The two ‘if’ blocks check for null and referential equality using the ReferenceEquals() method defined in the Object class. Line 23 is where I’m doing the actual check on the properties of the Product instances. This is what returns the ‘True’ for us when we run the application. I have also overridden the Object.Equals() method which calls the Equals() method of the interface. One thing to remember is that anytime you override the Equals() method, its’ a good practice to override the GetHashCode() method and overload the ‘==’ and the ‘!=’ operators. For detailed information on this, please read this and this. Since we’ve overloaded the operators as well, we get ‘True’ when we do actions like: 1: Console.WriteLine(products1.Contains(products2[0])); 2: Console.WriteLine(products1[0] == products2[0]); This completes the full circle on the SequenceEqual() method. See the code used in the article here.

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  • c# How to find if two objects are equal

    - by Simon G
    Hi, I'm needing to know the best way to compare two objects and to find out if there equal. I'm overriding both GethashCode and Equals. So a basic class looks like: public class Test { public int Value { get; set; } public string String1 { get; set; } public string String2 { get; set; } public override int GetHashCode() { return Value ^ String1.GetHashCode() ^ String2.GetHashCode(); } public override bool Equals( object obj ) { return GetHashCode() == obj.GetHashCode(); } } So for testing purposes I created two objects: Test t = new Test() { Value = 1, String1 ="One", String2 = "One" }; Test t2 = new Test() { Value = 1, String1 = "Two", String2 = "Two" }; bool areEqual = t.Equals( t2 ); In testing this areEqual returns true event though both objects are different. I realise this is because String1 and String2 are the same value in each object and thus cancels each other out when hashing. Is there a better way off hashing object that the method I have that will resolve my issue?

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  • Looking for a non-cryptographic hash function that returns a single character

    - by makerofthings7
    Suppose I have a dictionary of ASCII words stored in uppercase. I also want to save those words into separate files so that the total word count of each file is approximately the same. By simply looking at the word I need to know which file it should be in (if it's there at all). Duplicate words should go into the same file and overwrite the last one. My first attempt at solving this problem is to use .NET's object.GetHashCode() function and .Trim() to get one of the "random" characters that pop up. I asked a similar question here If I only use one character of object.GetHashCode() I would get a hash code character of A..Z or 0..9. However saving the result of GetHashCode to disk is a no-no so I need a substitute. Question: What algorithm (or subset of an algorithm) is appropriate for pigeonholing strings into a single character or range of characters (Like hex 0..F offers 16 chars)? Real world usage: I'll use this answer to modify the Partition key used in Azure Table storage as described here

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  • Distinctly LINQ &ndash; Getting a Distinct List of Objects

    - by David Totzke
    Let’s say that you have a list of objects that contains duplicate items and you want to extract a subset of distinct items.  This is pretty straight forward in the trivial case where the duplicate objects are considered the same such as in the following example: List<int> ages = new List<int> { 21, 46, 46, 55, 17, 21, 55, 55 }; IEnumerable<int> distinctAges = ages.Distinct(); Console.WriteLine("Distinct ages:"); foreach (int age in distinctAges) { Console.WriteLine(age); } /* This code produces the following output: Distinct ages: 21 46 55 17 */ What if you are working with reference types instead?  Imagine a list of search results where items in the results, while unique in and of themselves, also point to a parent.  We’d like to be able to select a bunch of items in the list but then see only a distinct list of parents.  Distinct isn’t going to help us much on its own as all of the items are distinct already.  Perhaps we can create a class with just the information we are interested in like the Id and Name of the parents.  public class SelectedItem { public int ItemID { get; set; } public string DisplayName { get; set; } } We can then use LINQ to populate a list containing objects with just the information we are interested in and then get rid of the duplicates. IEnumerable<SelectedItem> list = (from item in ResultView.SelectedRows.OfType<Contract.ReceiptSelectResults>() select new SelectedItem { ItemID = item.ParentId, DisplayName = item.ParentName }) .Distinct(); Most of you will have guessed that this didn’t work.  Even though some of our objects are now duplicates, because we are working with reference types, it doesn’t matter that their properties are the same, they’re still considered unique.  What we need is a way to define equality for the Distinct() extension method. IEqualityComparer<T> Looking at the Distinct method we see that there is an overload that accepts an IEqualityComparer<T>.  We can simply create a class that implements this interface and that allows us to define equality for our SelectedItem class. public class SelectedItemComparer : IEqualityComparer<SelectedItem> { public new bool Equals(SelectedItem abc, SelectedItem def) { return abc.ItemID == def.ItemID && abc.DisplayName == def.DisplayName; } public int GetHashCode(SelectedItem obj) { string code = obj.DisplayName + obj.ItemID.ToString(); return code.GetHashCode(); } } In the Equals method we simply do whatever comparisons are necessary to determine equality and then return true or false.  Take note of the implementation of the GetHashCode method.  GetHashCode must return the same value for two different objects if our Equals method says they are equal.  Get this wrong and your comparer won’t work .  Even though the Equals method returns true, mismatched hash codes will cause the comparison to fail.  For our example, we simply build a string from the properties of the object and then call GetHashCode() on that. Now all we have to do is pass an instance of our IEqualitlyComarer<T> to Distinct and all will be well: IEnumerable<SelectedItem> list =     (from item in ResultView.SelectedRows.OfType<Contract.ReceiptSelectResults>()         select new SelectedItem { ItemID = item.dahfkp, DisplayName = item.document_code })                         .Distinct(new SelectedItemComparer());   Enjoy. Dave Just because I can… Technorati Tags: LINQ,C#

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  • Entity Framework 4.0 and DDD patterns

    - by Voice
    Hi everybody I use EntityFramework as ORM and I have simple POCO Domain Model with two base classes that represent Value Object and Entity Object Patterns (Evans). These two patterns is all about equality of two objects, so I overrode Equals and GetHashCode methods. Here are these two classes: public abstract class EntityObject<T>{ protected T _ID = default(T); public T ID { get { return _ID; } protected set { _ID = value; } } public sealed override bool Equals(object obj) { EntityObject<T> compareTo = obj as EntityObject<T>; return (compareTo != null) && ((HasSameNonDefaultIdAs(compareTo) || (IsTransient && compareTo.IsTransient)) && HasSameBusinessSignatureAs(compareTo)); } public virtual void MakeTransient() { _ID = default(T); } public bool IsTransient { get { return _ID == null || _ID.Equals(default(T)); } } public override int GetHashCode() { if (default(T).Equals(_ID)) return 0; return _ID.GetHashCode(); } private bool HasSameBusinessSignatureAs(EntityObject<T> compareTo) { return ToString().Equals(compareTo.ToString()); } private bool HasSameNonDefaultIdAs(EntityObject<T> compareTo) { return (_ID != null && !_ID.Equals(default(T))) && (compareTo._ID != null && !compareTo._ID.Equals(default(T))) && _ID.Equals(compareTo._ID); } public override string ToString() { StringBuilder str = new StringBuilder(); str.Append(" Class: ").Append(GetType().FullName); if (!IsTransient) str.Append(" ID: " + _ID); return str.ToString(); } } public abstract class ValueObject<T, U> : IEquatable<T> where T : ValueObject<T, U> { private static List<PropertyInfo> Properties { get; set; } private static Func<ValueObject<T, U>, PropertyInfo, object[], object> _GetPropValue; static ValueObject() { Properties = new List<PropertyInfo>(); var propParam = Expression.Parameter(typeof(PropertyInfo), "propParam"); var target = Expression.Parameter(typeof(ValueObject<T, U>), "target"); var indexPar = Expression.Parameter(typeof(object[]), "indexPar"); var call = Expression.Call(propParam, typeof(PropertyInfo).GetMethod("GetValue", new[] { typeof(object), typeof(object[]) }), new[] { target, indexPar }); var lambda = Expression.Lambda<Func<ValueObject<T, U>, PropertyInfo, object[], object>>(call, target, propParam, indexPar); _GetPropValue = lambda.Compile(); } public U ID { get; protected set; } public override Boolean Equals(Object obj) { if (ReferenceEquals(null, obj)) return false; if (obj.GetType() != GetType()) return false; return Equals(obj as T); } public Boolean Equals(T other) { if (ReferenceEquals(null, other)) return false; if (ReferenceEquals(this, other)) return true; foreach (var property in Properties) { var oneValue = _GetPropValue(this, property, null); var otherValue = _GetPropValue(other, property, null); if (null == oneValue && null == otherValue) return false; if (false == oneValue.Equals(otherValue)) return false; } return true; } public override Int32 GetHashCode() { var hashCode = 36; foreach (var property in Properties) { var propertyValue = _GetPropValue(this, property, null); if (null == propertyValue) continue; hashCode = hashCode ^ propertyValue.GetHashCode(); } return hashCode; } public override String ToString() { var stringBuilder = new StringBuilder(); foreach (var property in Properties) { var propertyValue = _GetPropValue(this, property, null); if (null == propertyValue) continue; stringBuilder.Append(propertyValue.ToString()); } return stringBuilder.ToString(); } protected static void RegisterProperty(Expression<Func<T, Object>> expression) { MemberExpression memberExpression; if (ExpressionType.Convert == expression.Body.NodeType) { var body = (UnaryExpression)expression.Body; memberExpression = body.Operand as MemberExpression; } else memberExpression = expression.Body as MemberExpression; if (null == memberExpression) throw new InvalidOperationException("InvalidMemberExpression"); Properties.Add(memberExpression.Member as PropertyInfo); } } Everything was OK until I tried to delete some related objects (aggregate root object with two dependent objects which was marked for cascade deletion): I've got an exception "The relationship could not be changed because one or more of the foreign-key properties is non-nullable". I googled this and found http://blog.abodit.com/2010/05/the-relationship-could-not-be-changed-because-one-or-more-of-the-foreign-key-properties-is-non-nullable/ I changed GetHashCode to base.GetHashCode() and error disappeared. But now it breaks all my code: I can't override GetHashCode for my POCO objects = I can't override Equals = I can't implement Value Object and Entity Object patters for my POCO objects. So, I appreciate any solutions, workarounds here etc.

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  • How to hide GetType() method from COM?

    - by ticky
    I made an automation Add-In for Excel, and I made several functions (formulas). I have a class which header looks like this (it is COM visible): [ClassInterface(ClassInterfaceType.AutoDual)] [ComVisible(true)] public class Functions {} In a list of methods, I see: ToString(), Equals(), GetHashCode() and GetType() methods. Since all methods of my class are COM visible, I should somehow hide those 4. I succeeded with 3 of them: ToString(), Equals(), GetHashCode() but GetType() cannot be overriden. Here is what I did with 3 of them: [ComVisible(false)] public override string ToString() { return base.ToString(); } [ComVisible(false)] public override bool Equals(object obj) { return base.Equals(obj); } [ComVisible(false)] public override int GetHashCode() { return base.GetHashCode(); } This doesn't work: [ComVisible(false)] public override Type GetType() { return base.GetType(); } Here is the error message in Visual Studio when compile: ..GetType()': cannot override inherited member 'object.GetType()' because it is not marked virtual, abstract, or override So, what should I do to hide the GetType() method from COM?

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  • Overriding Object.Equals() instance method in C#; now Code Analysis / FxCop warning CA2218: "should

    - by Chris W. Rea
    I've got a complex class in my C# project on which I want to be able to do equality tests. It is not a trivial class; it contains a variety of scalar properties as well as references to other objects and collections (e.g. IDictionary). For what it's worth, my class is sealed. To enable a performance optimization elsewhere in my system (an optimization that avoids a costly network round-trip), I need to be able to compare instances of these objects to each other for equality – other than the built-in reference equality – and so I'm overriding the Object.Equals() instance method. However, now that I've done that, Visual Studio 2008's Code Analysis a.k.a. FxCop, which I keep enabled by default, is raising the following warning: warning : CA2218 : Microsoft.Usage : Since 'MySuperDuperClass' redefines Equals, it should also redefine GetHashCode. I think I understand the rationale for this warning: If I am going to be using such objects as the key in a collection, the hash code is important. i.e. see this question. However, I am not going to be using these objects as the key in a collection. Ever. Feeling justified to suppress the warning, I looked up code CA2218 in the MSDN documentation to get the full name of the warning so I could apply a SuppressMessage attribute to my class as follows: [SuppressMessage("Microsoft.Naming", "CA2218:OverrideGetHashCodeOnOverridingEquals", Justification="This class is not to be used as key in a hashtable.")] However, while reading further, I noticed the following: How to Fix Violations To fix a violation of this rule, provide an implementation of GetHashCode. For a pair of objects of the same type, you must ensure that the implementation returns the same value if your implementation of Equals returns true for the pair. When to Suppress Warnings ----- Do not suppress a warning from this rule. [arrow & emphasis mine] So, I'd like to know: Why shouldn't I suppress this warning as I was planning to? Doesn't my case warrant suppression? I don't want to code up an implementation of GetHashCode() for this object that will never get called, since my object will never be the key in a collection. If I wanted to be pedantic, instead of suppressing, would it be more reasonable for me to override GetHashCode() with an implementation that throws a NotImplementedException? Update: I just looked this subject up again in Bill Wagner's good book Effective C#, and he states in "Item 10: Understand the Pitfalls of GetHashCode()": If you're defining a type that won't ever be used as the key in a container, this won't matter. Types that represent window controls, web page controls, or database connections are unlikely to be used as keys in a collection. In those cases, do nothing. All reference types will have a hash code that is correct, even if it is very inefficient. [...] In most types that you create, the best approach is to avoid the existence of GetHashCode() entirely. ... that's where I originally got this idea that I need not be concerned about GetHashCode() always.

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  • C# ref question again?

    - by TheMachineCharmer
    class Foo { public int A { get; set; } } class Program { static void Main(string[] args) { var f = new Foo(); var ff = f; Console.WriteLine(f.GetHashCode()); Console.WriteLine(ff.GetHashCode()); FooFoo(ref f); BarBar(f); } private static void BarBar(Foo f) { Console.WriteLine(f.GetHashCode()); } private static void FooFoo(ref Foo f) { Console.WriteLine(f.GetHashCode()); } } OUTPUT: 58225482 58225482 58225482 58225482 What is the difference between FooFoo and BarBar?

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  • LINQ: Enhancing Distinct With The SelectorEqualityComparer

    - by Paulo Morgado
    On my last post, I introduced the PredicateEqualityComparer and a Distinct extension method that receives a predicate to internally create a PredicateEqualityComparer to filter elements. Using the predicate, greatly improves readability, conciseness and expressiveness of the queries, but it can be even better. Most of the times, we don’t want to provide a comparison method but just to extract the comaprison key for the elements. So, I developed a SelectorEqualityComparer that takes a method that extracts the key value for each element. Something like this: public class SelectorEqualityComparer<TSource, Tkey> : EqualityComparer<TSource> where Tkey : IEquatable<Tkey> { private Func<TSource, Tkey> selector; public SelectorEqualityComparer(Func<TSource, Tkey> selector) : base() { this.selector = selector; } public override bool Equals(TSource x, TSource y) { Tkey xKey = this.GetKey(x); Tkey yKey = this.GetKey(y); if (xKey != null) { return ((yKey != null) && xKey.Equals(yKey)); } return (yKey == null); } public override int GetHashCode(TSource obj) { Tkey key = this.GetKey(obj); return (key == null) ? 0 : key.GetHashCode(); } public override bool Equals(object obj) { SelectorEqualityComparer<TSource, Tkey> comparer = obj as SelectorEqualityComparer<TSource, Tkey>; return (comparer != null); } public override int GetHashCode() { return base.GetType().Name.GetHashCode(); } private Tkey GetKey(TSource obj) { return (obj == null) ? (Tkey)(object)null : this.selector(obj); } } Now I can write code like this: .Distinct(new SelectorEqualityComparer<Source, Key>(x => x.Field)) And, for improved readability, conciseness and expressiveness and support for anonymous types the corresponding Distinct extension method: public static IEnumerable<TSource> Distinct<TSource, TKey>(this IEnumerable<TSource> source, Func<TSource, TKey> selector) where TKey : IEquatable<TKey> { return source.Distinct(new SelectorEqualityComparer<TSource, TKey>(selector)); } And the query is now written like this: .Distinct(x => x.Field) For most usages, it’s simpler than using a predicate.

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  • SortList duplicated key, but it shouldn't

    - by Luca
    I have a class which implements IList interface. I requires a "sorted view" of this list, but without modifying it (I cannot sort directly the IList class). These view shall be updated when the original list is modified, keeping items sorted. So, I've introduced a SortList creation method which create a SortList which has a comparer for the specific object contained in the original list. Here is the snippet of code: public class MyList<T> : ICollection, IList<T> { ... public SortedList CreateSortView(string property) { try { Lock(); SortListView sortView; if (mSortListViews.ContainsKey(property) == false) { // Create sorted view sortView = new SortListView(property, Count); mSortListViews.Add(property, sortView); foreach (T item in Items) sortView.Add(item); } else sortView = mSortListViews[property]; sortView.ReferenceCount++; return (sortView); } finally { Unlock(); } } public void DeleteSortView(string property) { try { Lock(); // Unreference sorted view mSortListViews[property].ReferenceCount--; // Remove sorted view if (mSortListViews[property].ReferenceCount == 0) mSortListViews.Remove(property); } finally { Unlock(); } } protected class SortListView : SortedList { /// <summary> /// /// </summary> /// <param name="property"></param> /// <param name="capacity"></param> public SortListView(string property, int capacity) : base(new GenericPropertyComparer(typeof(T).GetProperty(property, BindingFlags.Instance | BindingFlags.Public)), capacity) { } /// <summary> /// Reference count. /// </summary> public int ReferenceCount = 0; /// <summary> /// /// </summary> /// <param name="item"></param> public void Add(T item) { Add(item, item); } /// <summary> /// /// </summary> /// <param name="item"></param> public void Remove(T item) { // Base implementation base.Remove(item); } /// <summary> /// Compare object on a generic property. /// </summary> class GenericPropertyComparer : IComparer { #region Constructors /// <summary> /// Construct a GenericPropertyComparer specifying the property to compare. /// </summary> /// <param name="property"> /// A <see cref="PropertyInfo"/> which specify the property to be compared. /// </param> /// <remarks> /// The <paramref name="property"/> parameter imply that the compared objects have the specified property. The property /// must be readable, and its type must implement the IComparable interface. /// </remarks> public GenericPropertyComparer(PropertyInfo property) { if (property == null) throw new ArgumentException("property doesn't specify a valid property"); if (property.CanRead == false) throw new ArgumentException("property specify a write-only property"); if (property.PropertyType.GetInterface("IComparable") == null) throw new ArgumentException("property type doesn't IComparable"); mSortingProperty = property; } #endregion #region IComparer Implementation public int Compare(object x, object y) { IComparable propX = (IComparable)mSortingProperty.GetValue(x, null); IComparable propY = (IComparable)mSortingProperty.GetValue(y, null); return (propX.CompareTo(propY)); } /// <summary> /// Sorting property. /// </summary> private PropertyInfo mSortingProperty = null; #endregion } } /// <summary> /// Sorted views of this ReactList. /// </summary> private Dictionary<string, SortListView> mSortListViews = new Dictionary<string, SortListView>(); } Practically, class users request to create a SortListView specifying the name of property which determine the sorting, and using the reflection each SortListView defined a IComparer which keep sorted the items. Whenever an item is added or removed from the original list, every created SortListView will be updated with the same operation. This seems good at first chance, but it creates me problems since it give me the following exception when adding items to the SortList: System.ArgumentException: Item has already been added. Key in dictionary: 'PowerShell_ISE [C:\Windows\sysWOW64\WindowsPowerShell\v1.0\PowerShell_ISE.exe]' Key being added: 'PowerShell_ISE [C:\Windows\system32\WindowsPowerShell\v1.0\PowerShell_ISE.exe]' As you can see from the exception message, thrown by SortedListView.Add(object), the string representation of the key (the list item object) is different (note the path of the executable). Why SortList give me that exception? To solve this I tried to implement a GetHashCode implementation for the underlying object, but without success: public override int GetHashCode() { return ( base.GetHashCode() ^ mApplicationName.GetHashCode() ^ mApplicationPath.GetHashCode() ^ mCommandLine.GetHashCode() ^ mWorkingDirectory.GetHashCode() ); }

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  • NHibernate MySQL Composite-Key

    - by LnDCobra
    I am trying to create a composite key that mimicks the set of PrimaryKeys in the built in MySQL.DB table. The Db primary key is as follows: Field | Type | Null | ---------------------------------- Host | char(60) | No | Db | char(64) | No | User | char(16) | No | This is my DataBasePrivilege.hbm.xml file <?xml version="1.0" encoding="utf-8" ?> <hibernate-mapping xmlns="urn:nhibernate-mapping-2.2" assembly="TGS.MySQL.DataBaseObjects" namespace="TGS.MySQL.DataBaseObjects"> <class name="TGS.MySQL.DataBaseObjects.DataBasePrivilege,TGS.MySQL.DataBaseObjects" table="db"> <composite-id name="CompositeKey" class="TGS.MySQL.DataBaseObjects.DataBasePrivilegePrimaryKey, TGS.MySQL.DataBaseObjects"> <key-property name="Host" column="Host" type="char" length="60" /> <key-property name="DataBase" column="Db" type="char" length="64" /> <key-property name="User" column="User" type="char" length="16" /> </composite-id> </class> </hibernate-mapping> The following are my 2 classes for my composite key: namespace TGS.MySQL.DataBaseObjects { public class DataBasePrivilege { public virtual DataBasePrivilegePrimaryKey CompositeKey { get; set; } } public class DataBasePrivilegePrimaryKey { public string Host { get; set; } public string DataBase { get; set; } public string User { get; set; } public override bool Equals(object obj) { if (ReferenceEquals(null, obj)) return false; if (ReferenceEquals(this, obj)) return true; if (obj.GetType() != typeof (DataBasePrivilegePrimaryKey)) return false; return Equals((DataBasePrivilegePrimaryKey) obj); } public bool Equals(DataBasePrivilegePrimaryKey other) { if (ReferenceEquals(null, other)) return false; if (ReferenceEquals(this, other)) return true; return Equals(other.Host, Host) && Equals(other.DataBase, DataBase) && Equals(other.User, User); } public override int GetHashCode() { unchecked { int result = (Host != null ? Host.GetHashCode() : 0); result = (result*397) ^ (DataBase != null ? DataBase.GetHashCode() : 0); result = (result*397) ^ (User != null ? User.GetHashCode() : 0); return result; } } } } And the following is the exception I am getting: Execute System.InvalidCastException: Unable to cast object of type 'System.Object[]' to type 'TGS.MySQL.DataBaseObjects.DataBasePrivilegePrimaryKey'. at (Object , GetterCallback ) at NHibernate.Bytecode.Lightweight.AccessOptimizer.GetPropertyValues(Object target) at NHibernate.Tuple.Component.PocoComponentTuplizer.GetPropertyValues(Object component) at NHibernate.Type.ComponentType.GetPropertyValues(Object component, EntityMode entityMode) at NHibernate.Type.ComponentType.GetHashCode(Object x, EntityMode entityMode) at NHibernate.Type.ComponentType.GetHashCode(Object x, EntityMode entityMode, ISessionFactoryImplementor factory) at NHibernate.Engine.EntityKey.GenerateHashCode() at NHibernate.Engine.EntityKey..ctor(Object identifier, String rootEntityName, String entityName, IType identifierType, Boolean batchLoadable, ISessionFactoryImplementor factory, EntityMode entityMode) at NHibernate.Engine.EntityKey..ctor(Object id, IEntityPersister persister, EntityMode entityMode) at NHibernate.Event.Default.DefaultLoadEventListener.OnLoad(LoadEvent event, LoadType loadType) at NHibernate.Impl.SessionImpl.FireLoad(LoadEvent event, LoadType loadType) at NHibernate.Impl.SessionImpl.Get(String entityName, Object id) at NHibernate.Impl.SessionImpl.Get(Type entityClass, Object id) at NHibernate.Impl.SessionImpl.Get[T](Object id) at TGS.MySQL.DataBase.DataProvider.GetDatabasePrivilegeByHostDbUser(String host, String db, String user) in C:\Documents and Settings\Michal\My Documents\Visual Studio 2008\Projects\TGS\TGS.MySQL.DataBase\DataProvider.cs:line 20 at TGS.UserAccountControl.UserAccountManager.GetDatabasePrivilegeByHostDbUser(String host, String db, String user) in C:\Documents and Settings\Michal\My Documents\Visual Studio 2008\Projects\TGS\TGS.UserAccountControl\UserAccountManager.cs:line 10 at TGS.UserAccountControlTest.UserAccountManagerTest.CanGetDataBasePrivilegeByHostDbUser() in C:\Documents and Settings\Michal\My Documents\Visual Studio 2008\Projects\TGS\TGS.UserAccountControlTest\UserAccountManagerTest.cs:line 12 I am new to NHibernate and any help would be appreciated. I just can't see where it is getting the object[] from? Is the composite key supposed to be object[]?

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  • NHibernate Pitfalls: Custom Types and Detecting Changes

    - by Ricardo Peres
    This is part of a series of posts about NHibernate Pitfalls. See the entire collection here. NHibernate supports the declaration of properties of user-defined types, that is, not entities, collections or primitive types. These are used for mapping a database columns, of any type, into a different type, which may not even be an entity; think, for example, of a custom user type that converts a BLOB column into an Image. User types must implement interface NHibernate.UserTypes.IUserType. This interface specifies an Equals method that is used for comparing two instances of the user type. If this method returns false, the entity is marked as dirty, and, when the session is flushed, will trigger an UPDATE. So, in your custom user type, you must implement this carefully so that it is not mistakenly considered changed. For example, you can cache the original column value inside of it, and compare it with the one in the other instance. Let’s see an example implementation of a custom user type that converts a Byte[] from a BLOB column into an Image: 1: [Serializable] 2: public sealed class ImageUserType : IUserType 3: { 4: private Byte[] data = null; 5: 6: public ImageUserType() 7: { 8: this.ImageFormat = ImageFormat.Png; 9: } 10: 11: public ImageFormat ImageFormat 12: { 13: get; 14: set; 15: } 16: 17: public Boolean IsMutable 18: { 19: get 20: { 21: return (true); 22: } 23: } 24: 25: public Object Assemble(Object cached, Object owner) 26: { 27: return (cached); 28: } 29: 30: public Object DeepCopy(Object value) 31: { 32: return (value); 33: } 34: 35: public Object Disassemble(Object value) 36: { 37: return (value); 38: } 39: 40: public new Boolean Equals(Object x, Object y) 41: { 42: return (Object.Equals(x, y)); 43: } 44: 45: public Int32 GetHashCode(Object x) 46: { 47: return ((x != null) ? x.GetHashCode() : 0); 48: } 49: 50: public override Int32 GetHashCode() 51: { 52: return ((this.data != null) ? this.data.GetHashCode() : 0); 53: } 54: 55: public override Boolean Equals(Object obj) 56: { 57: ImageUserType other = obj as ImageUserType; 58: 59: if (other == null) 60: { 61: return (false); 62: } 63: 64: if (Object.ReferenceEquals(this, other) == true) 65: { 66: return (true); 67: } 68: 69: return (this.data.SequenceEqual(other.data)); 70: } 71: 72: public Object NullSafeGet(IDataReader rs, String[] names, Object owner) 73: { 74: Int32 index = rs.GetOrdinal(names[0]); 75: Byte[] data = rs.GetValue(index) as Byte[]; 76: 77: this.data = data as Byte[]; 78: 79: if (data == null) 80: { 81: return (null); 82: } 83: 84: using (MemoryStream stream = new MemoryStream(this.data ?? new Byte[0])) 85: { 86: return (Image.FromStream(stream)); 87: } 88: } 89: 90: public void NullSafeSet(IDbCommand cmd, Object value, Int32 index) 91: { 92: if (value != null) 93: { 94: Image data = value as Image; 95: 96: using (MemoryStream stream = new MemoryStream()) 97: { 98: data.Save(stream, this.ImageFormat); 99: value = stream.ToArray(); 100: } 101: } 102: 103: (cmd.Parameters[index] as DbParameter).Value = value ?? DBNull.Value; 104: } 105: 106: public Object Replace(Object original, Object target, Object owner) 107: { 108: return (original); 109: } 110: 111: public Type ReturnedType 112: { 113: get 114: { 115: return (typeof(Image)); 116: } 117: } 118: 119: public SqlType[] SqlTypes 120: { 121: get 122: { 123: return (new SqlType[] { new SqlType(DbType.Binary) }); 124: } 125: } 126: } In this case, we need to cache the original Byte[] data because it’s not easy to compare two Image instances, unless, of course, they are the same.

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  • Resolving collisions between dynamic game objects

    - by TheBroodian
    I've been building a 2D platformer for some time now, I'm getting to the point where I am adding dynamic objects to the stage for testing. This has prompted me to consider how I would like my character and other objects to behave when they collide. A typical staple in many 2D platformer type games is that the player takes damage upon touching an enemy, and then essentially becomes able to pass through enemies during a period of invulnerability, and at the same time, enemies are able to pass through eachother freely. I personally don't want to take this approach, it feels strange to me that the player should receive arbitrary damage for harmless contact to an enemy, despite whether the enemy is attacking or not, and I would like my enemies' interactions between each other (and my player) to be a little more organic, so to speak. In my head I sort of have this idea where a game object (player, or non player) would be able to push other game objects around by manner of 'pushing' each other out of one anothers' bounding boxes if there is an intersection, and maybe correlate the repelling force to how much their bounding boxes are intersecting. The problem I'm experiencing is I have no idea what the math might look like for something like this? I'll show what work I've done so far, it sort of works, but it's jittery, and generally not quite what I would pass in a functional game: //Clears the anti-duplicate buffer collisionRecord.Clear(); //pick a thing foreach (GameObject entity in entities) { //pick another thing foreach (GameObject subject in entities) { //check to make sure both things aren't the same thing if (!ReferenceEquals(entity, subject)) { //check to see if thing2 is in semi-near proximity to thing1 if (entity.WideProximityArea.Intersects(subject.CollisionRectangle) || entity.WideProximityArea.Contains(subject.CollisionRectangle)) { //check to see if thing2 and thing1 are colliding. if (entity.CollisionRectangle.Intersects(subject.CollisionRectangle) || entity.CollisionRectangle.Contains(subject.CollisionRectangle) || subject.CollisionRectangle.Contains(entity.CollisionRectangle)) { //check if we've already resolved their collision or not. if (!collisionRecord.ContainsKey(entity.GetHashCode())) { //more duplicate resolution checking. if (!collisionRecord.ContainsKey(subject.GetHashCode())) { //if thing1 is traveling right... if (entity.Velocity.X > 0) { //if it isn't too far to the right... if (subject.CollisionRectangle.Contains(new Microsoft.Xna.Framework.Rectangle(entity.CollisionRectangle.Right, entity.CollisionRectangle.Y, 1, entity.CollisionRectangle.Height)) || subject.CollisionRectangle.Intersects(new Microsoft.Xna.Framework.Rectangle(entity.CollisionRectangle.Right, entity.CollisionRectangle.Y, 1, entity.CollisionRectangle.Height))) { //Find how deep thing1 is intersecting thing2's collision box; float offset = entity.CollisionRectangle.Right - subject.CollisionRectangle.Left; //Move both things in opposite directions half the length of the intersection, pushing thing1 to the left, and thing2 to the right. entity.Velocities.Add(new Vector2(-(((offset * 4) * (float)gameTime.ElapsedGameTime.TotalMilliseconds)), 0)); subject.Velocities.Add(new Vector2((((offset * 4) * (float)gameTime.ElapsedGameTime.TotalMilliseconds)), 0)); } } //if thing1 is traveling left... if (entity.Velocity.X < 0) { //if thing1 isn't too far left... if (entity.CollisionRectangle.Contains(new Microsoft.Xna.Framework.Rectangle(subject.CollisionRectangle.Right, subject.CollisionRectangle.Y, 1, subject.CollisionRectangle.Height)) || entity.CollisionRectangle.Intersects(new Microsoft.Xna.Framework.Rectangle(subject.CollisionRectangle.Right, subject.CollisionRectangle.Y, 1, subject.CollisionRectangle.Height))) { //Find how deep thing1 is intersecting thing2's collision box; float offset = subject.CollisionRectangle.Right - entity.CollisionRectangle.Left; //Move both things in opposite directions half the length of the intersection, pushing thing1 to the right, and thing2 to the left. entity.Velocities.Add(new Vector2((((offset * 4) * (float)gameTime.ElapsedGameTime.TotalMilliseconds)), 0)); subject.Velocities.Add(new Vector2(-(((offset * 4) * (float)gameTime.ElapsedGameTime.TotalMilliseconds)), 0)); } } //Make record that thing1 and thing2 have interacted and the collision has been solved, so that if thing2 is picked next in the foreach loop, it isn't checked against thing1 a second time before the next update. collisionRecord.Add(entity.GetHashCode(), subject.GetHashCode()); } } } } } } } } One of the biggest issues with my code aside from the jitteriness is that if one character were to land on top of another character, it very suddenly and abruptly resolves the collision, whereas I would like a more subtle and gradual resolution. Any thoughts or ideas are incredibly welcome and helpful.

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  • How does formatting works with a PowerShell function that returns a set of elements?

    - by Steve B
    If I write this small function : function Foo { Get-Process | % { $_ } } And if I run Foo It displays only a small subset of properties: PS C:\Users\Administrator> foo Handles NPM(K) PM(K) WS(K) VM(M) CPU(s) Id ProcessName ------- ------ ----- ----- ----- ------ -- ----------- 86 10 1680 412 31 0,02 5916 alg 136 10 2772 2356 78 0,06 3684 atieclxx 123 7 1780 1040 33 0,03 668 atiesrxx ... ... But even if only 8 columns are shown, there are plenty of other properties (as foo | gm is showing). What is causing this function to show only this 8 properties? I'm actually trying to build a similar function that is returning complex objects from a 3rd party .Net library. The library is flatting a 2 level hierarchy of objects : function Actual { $someDotnetObject.ACollectionProperty.ASecondLevelCollection | % { $_ } } This method is dumping the objects in a list form (one line per property). How can I control what is displayed, keeping the actual object available? I have tried this : function Actual { $someDotnetObject.ACollectionProperty.ASecondLevelCollection | % { $_ } | format-table Property1, Property2 } It shows in a console the expected table : Property1 Property2 --------- --------- ValA ValD ValB ValE ValC ValF But I lost my objects. Running Get-Member on the result shows : TypeName: Microsoft.PowerShell.Commands.Internal.Format.FormatStartData Name MemberType Definition ---- ---------- ---------- Equals Method bool Equals(System.Object obj) GetHashCode Method int GetHashCode() GetType Method type GetType() ToString Method string ToString() autosizeInfo Property Microsoft.PowerShell.Commands.Internal.Format.AutosizeInfo autosizeInfo {get;set;} ClassId2e4f51ef21dd47e99d3c952918aff9cd Property System.String ClassId2e4f51ef21dd47e99d3c952918aff9cd {get;} groupingEntry Property Microsoft.PowerShell.Commands.Internal.Format.GroupingEntry groupingEntry {get;set;} pageFooterEntry Property Microsoft.PowerShell.Commands.Internal.Format.PageFooterEntry pageFooterEntry {get;set;} pageHeaderEntry Property Microsoft.PowerShell.Commands.Internal.Format.PageHeaderEntry pageHeaderEntry {get;set;} shapeInfo Property Microsoft.PowerShell.Commands.Internal.Format.ShapeInfo shapeInfo {get;set;} TypeName: Microsoft.PowerShell.Commands.Internal.Format.GroupStartData Name MemberType Definition ---- ---------- ---------- Equals Method bool Equals(System.Object obj) GetHashCode Method int GetHashCode() GetType Method type GetType() ToString Method string ToString() ClassId2e4f51ef21dd47e99d3c952918aff9cd Property System.String ClassId2e4f51ef21dd47e99d3c952918aff9cd {get;} groupingEntry Property Microsoft.PowerShell.Commands.Internal.Format.GroupingEntry groupingEntry {get;set;} shapeInfo Property Microsoft.PowerShell.Commands.Internal.Format.ShapeInfo shapeInfo {get;set;} Instead of showing the 2nd level child object members. In this case, I can't pipe the result to functions waiting for this type of argument. How does Powershell is supposed to handle such scenario?

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  • Remove duplicates from DataTable and custom IEqualityComparer<DataRow>

    - by abatishchev
    How have I to implement IEqualityComparer<DataRow> to remove duplicates rows from a DataTable with next structure: ID primary key, col_1, col_2, col_3, col_4 The default comparer doesn't work because each row has it's own, unique primary key. How to implement IEqualityComparer<DataRow> that will skip primary key and compare only data remained. I have something like this: public class DataRowComparer : IEqualityComparer<DataRow> { public bool Equals(DataRow x, DataRow y) { return x.ItemArray.Except(new object[] { x[x.Table.PrimaryKey[0].ColumnName] }) == y.ItemArray.Except(new object[] { y[y.Table.PrimaryKey[0].ColumnName] }); } public int GetHashCode(DataRow obj) { return obj.ToString().GetHashCode(); } } and public static DataTable RemoveDuplicates(this DataTable table) { return (table.Rows.Count > 0) ? table.AsEnumerable().Distinct(new DataRowComparer()).CopyToDataTable() : table; } but it calls only GetHashCode() and doesn't call Equals()

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  • linq Except and custom IEqualityComparer

    - by Joe
    I'm trying to implement a custom comparer on two lists of strings and use the .Except() linq method to get those that aren't one one of the lists. The reason I'm doing a custom comparer is because I need to do a "fuzzy" compare, i.e. one string on one list could be embedded inside a string on the other list. I've made the following comparer ` public class ItemFuzzyMatchComparer : IEqualityComparer { bool IEqualityComparer<string>.Equals(string x, string y) { return (x.Contains(y) || y.Contains(x)); } int IEqualityComparer<string>.GetHashCode(string obj) { if (Object.ReferenceEquals(obj, null)) return 0; return obj.GetHashCode(); } } ` When I debug, the only breakpoint that hits is in the GetHashCode() method. The Equals() never gets touched. Any ideas?

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  • Should I forward the a call to .Equals onto .Equals<T>?

    - by Jaimal Chohan
    So, I've got you bog standard c# object, overriding Equalsand implementing IEquatable public override int GetHashCode() { return _name.GetHashCode(); } public override bool Equals(object obj) { return Equals(obj as Tag) } #region IEquatable<Tag> Members public bool Equals(Tag other) { if (other == null) return false; else return _name == other._name; } #endregion Now, for some reason, I used to think that forwarding the calls from Equals into Equals was bad, no idea why, perhaps I read it a long time ago, anyway I'd write separate (but logically same) code for each method. Now I think forwarding Equals to Equals is okay, for obvious reasons, but for the life me I can't remember why I thought it wasn't before. Any thoughts?

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  • Generic IEqualityComparer

    - by Nettuce
    A generic equality comparer that takes a property expression or a comparison Func public class GenericComparer<T> : IEqualityComparer<T> where T : class         {             private readonly Func<T, T, bool> comparerExpression;             private readonly string propertyName;             public GenericComparer(Func<T, T, bool> comparerExpression)             {                 this.comparerExpression = comparerExpression;             }             public GenericComparer(Expression<Func<T, object>> propertyExpression)             {                 propertyName = (propertyExpression.Body is UnaryExpression ? (MemberExpression)((UnaryExpression)propertyExpression.Body).Operand : (MemberExpression)propertyExpression.Body).Member.Name;             }             public bool Equals(T x, T y)             {                 return comparerExpression == null ? x.GetType().GetProperty(propertyName).GetValue(x, null).Equals(y.GetType().GetProperty(propertyName).GetValue(y, null)) : comparerExpression.Invoke(x, y);             }             public int GetHashCode(T obj)             {                 return obj.ToString().GetHashCode();             }         }

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  • NUnit doesn't work well with Assert.AreEqual

    - by stasal
    Hi! I'm new to unit-testing and NUit in particular. I'm just typing some examples from the book which refers to Java and JUnit. But I'm using C# instead. The problem is: I've got a class with overriden methods such as Equals() and GetHashCode(), but when I am trying to compare two objects of this class with Assert.AreEqual() my code is not called, so I get an exception. Assert.True(MyClass.Equals(MyClass2)) does work well. But I don't wanna use this construction instead of Assert.AreEqual(). Where the problem can be? Here is the class: public class Money { public int amount; protected string currency; public Money(int amount, string currency) { this.amount = amount; this.currency = currency; } public new bool Equals(object obj) { if (obj == null) return false; Money money = (Money)obj; return (amount == money.amount) && (Currency().Equals(money.Currency())); } public new int GetHashCode() { return (string.Format("{0}{1}", amount, currency)).GetHashCode(); } public static Money Dollar(int amount) { return new Money(amount, "USD"); } public static Money Franc(int amount) { return new Money(amount, "CHF"); } public Money Times(int multiplier) { return new Money(amount * multiplier, currency); } public string Currency() { return currency; } } And the test method itself: [TestFixture] public class DollarTest { [Test] public void TestMultiplication() { Money five = Money.Dollar(5); Assert.True(Money.Dollar(10).Equals(five.Times(2))); // ok Assert.AreEqual(Money.Dollar(10), five.Times(2)); // fails } } Thanks.

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  • How to map string keys to unique integer IDs?

    - by Marek
    I have some data that comes regularily as a dump from a data souce with a string natural key that is long (up to 60 characters) and not relevant to the end user. I am using this key in a url. This makes urls too long and user unfriendly. I would like to transform the string keys into integers with the following requirements: The source dataset will change over time. The ID should be: non negative integer unique and constant even if the set of input keys changes preferrably reversible back to key (not a strong requirement) The database is rebuilt from scratch every time so I can not remember the already assigned IDs and match the new data set to existing IDs and generate sequential IDs for the added keys. There are currently around 30000 distinct keys and the set is constantly growing. How to implement a function that will map string keys to integer IDs? What I have thought about: 1. Built-in string.GetHashCode: ID(key) = Math.Abs(key.GetHashCode()) is not guaranteed to be unique (not reversible) 1.1 "Re-hashing" the built-in GetHashCode until a unique ID is generated to prevent collisions. existing IDs may change if something colliding is added to the beginning of the input data set 2. a perfect hashing function I am not sure if this can generate constant IDs if the set of inputs changes (not reversible) 3. translate to base 36/64/?? does not shorten the long keys enough What are the other options?

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