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• Disable caching in JPA (eclipselink)

  - by James

  Hi, I want to use JPA (eclipselink) to get data from my database. The database is changed by a number of other sources and I therefore want to go back to the database for every find I execute. I have read a number of posts on disabling the cache but this does not seem to be working. Any ideas? I am trying to execute the following code: EntityManagerFactory entityManagerFactory = Persistence.createEntityManagerFactory("default"); EntityManager em = entityManagerFactory.createEntityManager(); MyLocation one = em.createNamedQuery("MyLocation.findMyLoc").getResultList().get(0); MyLocation two = em.createNamedQuery("MyLocation.findMyLoc").getResultList().get(0); System.out.println(one==two); one==two is true while I want it to be false. I have tried adding each/all the following to my persistence.xml <property name="eclipselink.cache.shared.default" value="false"/> <property name="eclipselink.cache.size.default" value="0"/> <property name="eclipselink.cache.type.default" value="None"/> I have also tried adding the @Cache annotation to the Entity itself: @Cache( type=CacheType.NONE, // Cache nothing expiry=0, alwaysRefresh=true ) Am I misunderstanding something? Thank you, James

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• Using ComplexType with ToList causes InvalidOperationException

  - by Chris Paynter

  I have this model namespace ProjectTimer.Models { public class TimerContext : DbContext { public TimerContext() : base("DefaultConnection") { } public DbSet<Project> Projects { get; set; } public DbSet<ProjectTimeSpan> TimeSpans { get; set; } } public class DomainBase { [Key] public int Id { get; set; } } public class Project : DomainBase { public UserProfile User { get; set; } public string Name { get; set; } public string Description { get; set; } public IList<ProjectTimeSpan> TimeSpans { get; set; } } [ComplexType] public class ProjectTimeSpan { public DateTime TimeStart { get; set; } public DateTime TimeEnd { get; set; } public bool Active { get; set; } } } When I try to use this action I get the exception The type 'ProjectTimer.Models.ProjectTimeSpan' has already been configured as an entity type. It cannot be reconfigured as a complex type. public ActionResult Index() { using (var db = new TimerContext()) { return View(db.Projects.ToList); } } The view is using the model @model IList<ProjectTimer.Models.Project> Can any one shine some light as to why this would be happening?

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• MySQL Connector for .NET - Is it REALLY mature?

  - by effkay

  After spending a miserable month with MySQL/.NET/EntityFramework, my findings: Support for Entity Framework is VERY primitive, please use it for student-subjects type of database. Kindly do not consider it using for serious development as they ARE STILL unable to sort out VERY BASIC things like: it DOES NOT support unsigned stuff it DOES NOT support unsigned columns as FK; if you try, it gives you a beautiful exception; "The specified value is not an instance of a valid constant type\r\nParameter name: value" [http://bugs.mysql.com/bug.php?id=44801] blob cannot store more then few KB; cannot compare null object with a column with a LEGAL null value [http://bugs.mysql.com/bug.php?id=49936] they are unable to write VERY PRIMITIVE check to return date as null if value in column is 0000-00-00 00:00:00 if you use Visual Studio; sorry; mysql/sun guys hate Microsoft, they will NOT LET you import more then two or three tables (for Micky Mouse type of tables, they allow five; but thats it) - if you try, it will throw TIME OUT error on your face ... unless you are smart enough to change the connection time in connection string Anyone who would like to add in above list? WISH I would have seen a list like this before I selected MySQL :(

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• Best pattern for storing (product) attributes in SQL Server

  - by EdH

  We are starting a new project where we need to store product and many product attributes in a database. The technology stack is MS SQL 2008 and Entity Framework 4.0 / LINQ for data access. The products (and Products Table) are pretty straightforward (a SKU, manufacturer, price, etc..). However there are also many attributes to store with each product (think industrial widgets). These may range from color to certification(s) to pipe size. Every product may have different attributes, and some may have multiples of the same attribute (Ex: Certifications). The current proposal is that we will basically have a name/value pair table with a FK back to the product ID in each row. An example of the attributes Table may look like this: ProdID AttributeName AttributeValue 123 Color Blue 123 FittingSize 1.25 123 Certification AS1111 123 Certification EE2212 123 Certification FM.3 456 Pipe 11 678 Color Red 999 Certification AE1111 ... Note: Attribute name would likely come from a lookup table or enum. So the main question here is: Is this the best pattern for doing something like this? How will the performance be? Queries will be based on a JOIN of the product and attributes table, and generally need many WHEREs to filter on specific attributes - the most common search will be to find a product based on a set of known/desired attributes. If anyone has any suggestions or a better pattern for this type of data, please let me know. Thanks! -Ed

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• Can't submit new object to WCF DataService because of Primary Key constraint

  - by Rob

  I've got a SQL database that uses Guid's for PK's and upon insert, it generates a NewId(). I have an EF data context setup pointing to that database with the primary keys setup with the Entity key:true, Setter:private and StoreGeneratedPattern:Identity because I want the DB to manage the keys and not have code set the PK property. I have an OData (System.Web.Data.Services.DataService) endpoint to access this data (just like: Hanselman did. I have another app that has a service reference to this service. Upon trying to create a new object from this reference (i.e. Product), the ProductId Primary Key is being defaulted to Guid.Empty when doing var serviceEntities = new ServiceEntities(serviceUri); //OData endpoint var product = new Product(); product.Name = "New Product"; serviceEntities.AddToProducts(product); serviceEntities.SaveChanges(); // error happens here When debugging, I look at the Product.ProductId property and it's set to Guid.Empty. When called SaveChanges, I do not want the ProductId field to be sent to the service. The response I get is: Error processing request stream. Property 'ProductId' is a read-only property and cannot be updated. Please make sure that this property is not present in the request payload. Is there a way to do this or what can I do to get this setup correctly and still have the DB generated the keys. Here is the same setup as the Product example above.

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• ASP.NET MVC Concurrency with RowVersion in Edit Action

  - by Jorin

  I'm wanting to do a simple edit form for our Issue Tracking app. For simplicity, the HttpGet Edit action looks something like this: // Issues/Edit/12 public ActionResult Edit(int id) { var thisIssue = edmx.Issues.First(i => i.IssueID == id); return View(thisIssue); } and then the HttpPost action looks something like this: [HttpPost] public ActionResult Edit(int id, FormCollection form) { // this is the dumb part where I grab the object before I update it. // concurrency is sidestepped here. var thisIssue = edmx.Issues.Single(c => c.IssueID == id); TryUpdateModel(thisIssue); if (ModelState.IsValid) { edmx.SaveChanges(); TempData["message"] = string.Format("Issue #{0} successfully modified.", id); return RedirectToAction("Index"); } return View(thisIssue); } Which works wonderfully. However, the concurrency check doesn't work because in the Post, I'm re-retreiving the current entity right before I attempt to update it. However, with EF, I don't know how to use the fanciness of SaveChanges() but attach my thisIssue to the context. I tried to call edmx.Issues.Attach(thisIssue) but I get The object cannot be attached because it is already in the object context. An object can only be reattached when it is in an unchanged state. How do I handle concurrency in MVC with EF and/or how do I properly Attach my edited object to the context? Thanks in advance

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• EntityFramework repository template- how to write GetByID lamba within a template class?

  - by FerretallicA

  I am trying to write a generic one-size-fits-most repository pattern template class for an Entity Framework-based project I'm currently working on. The (heavily simplified) interface is: internal interface IRepository<T> where T : class { T GetByID(int id); IEnumerable<T> GetAll(); IEnumerable<T> Query(Func<T, bool> filter); } GetByID is proving to be the killer. In the implementation: public class Repository<T> : IRepository<T>,IUnitOfWork<T> where T : class { // etc... public T GetByID(int id) { return this.ObjectSet.Single<T>(t=>t.ID == id); } t=t.ID == id is the particular bit I'm struggling with. Is it even possible to write lamba functions like that within template classes where no class-specific information is going to be available?

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• edmx - The operation could not be completed - After adding Inheritance

  - by vdh_ant

  Hey guys I have an edmx model which I have draged 2 tables onto - One called 'File' and the other 'ApplicaitonFile'. These two tables have a 1 to 1 relationship in the database. If I stop here everything works fine. But in my model, I want 'ApplicaitonFile' to inherit from 'File'. So I delete the 1 to 1 relationship then configure 'ApplicaitonFile' from 'File' and then remove the FileId from 'ApplicaitonFile' which was the primary key. (Note I am following the instructions from here). If I leave the model open at this point everything is fine, but as soon as I close it, if I try and reopen it again I get the following error "The operation could not be completed". I have been searching for a solution and found this - http://stackoverflow.com/questions/944050/entity-model-does-not-load but as far as I can tell I don't have a duplicate InheritanceConnectors (although I don't know exactly what I'm looking for but I can't see anything out of the ordinary - like 2 connectors with the same name) and the relationship I originally have is a 1 to 1 not a 1 to 0..1 Any ideas???

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• Typecasting EnityObject

  - by AJ

  Hello, I'm new to C# and am stuck on the following. I have a Silverlight web service that uses LINQ to query a ADO.NET entity object. e.g.: [OperationContract] public List<Customer> GetData() { using (TestEntities ctx = new TestEntities()) { var data = from rec in ctx.Customer select rec; return data.ToList(); } } This works fine, but what I want to do is to make this more abstract. The first step would be to return a List<EntityObject> but this gives a compiler error, e.g.: [OperationContract] public List<EntityObject> GetData() { using (TestEntities ctx = new TestEntities()) { var data = from rec in ctx.Customer select rec; return data.ToList(); } } The error is: Error 1 Cannot implicitly convert type 'System.Collections.Generic.List<SilverlightTest.Web.Customer>' to 'System.Collections.Generic.IEnumerable<System.Data.Objects.DataClasses.EntityObject>'. An explicit conversion exists (are you missing a cast?) What am i doing wrong? Thanks, AJ

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• Generic list typecasting problem

  - by AJ

  Hello, I'm new to C# and am stuck on the following. I have a Silverlight web service that uses LINQ to query a ADO.NET entity object. e.g.: [OperationContract] public List<Customer> GetData() { using (TestEntities ctx = new TestEntities()) { var data = from rec in ctx.Customer select rec; return data.ToList(); } } This works fine, but what I want to do is to make this more abstract. The first step would be to return a List<EntityObject> but this gives a compiler error, e.g.: [OperationContract] public List<EntityObject> GetData() { using (TestEntities ctx = new TestEntities()) { var data = from rec in ctx.Customer select rec; return data.ToList(); } } The error is: Error 1 Cannot implicitly convert type 'System.Collections.Generic.List<SilverlightTest.Web.Customer>' to 'System.Collections.Generic.IEnumerable<System.Data.Objects.DataClasses.EntityObject>'. An explicit conversion exists (are you missing a cast?) What am i doing wrong? Thanks, AJ

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• Disable chaching in JPA (eclipselink)

  - by James

  Hi, I want to use JPA (eclipselink) to get data from my database. The database is changed by a number of other sources and I therefore want to go back to the database for every find I execute. I have read a number of posts on disabling the cache but this does not seem to be working. Any ideas? I am trying to execute the following code: EntityManagerFactory entityManagerFactory = Persistence.createEntityManagerFactory("default"); EntityManager em = entityManagerFactory.createEntityManager(); MyLocation one = em.createNamedQuery("MyLocation.findMyLoc").getResultList().get(0); MyLocation two = em.createNamedQuery("MyLocation.findMyLoc").getResultList().get(0); System.out.println(one==two); one==two is true while I want it to be false. I have tried adding each/all the following to my persistence.xml <property name="eclipselink.cache.shared.default" value="false"/> <property name="eclipselink.cache.size.default" value="0"/> <property name="eclipselink.cache.type.default" value="None"/> I have also tried adding the @Cache annotation to the Entity itself: @Cache( type=CacheType.NONE, // Cache nothing expiry=0, alwaysRefresh=true ) Am I misunderstanding something? Thank you, James

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• WCF Service invalid with Silverlight

  - by Echilon

  I'm trying to get WCF working with Silverlight. I'm a total beginner to WCF but have written asmx services in the past. For some reason when I uncomment more than one method in my service Silverlight refuses to let me use it, saying it is invalid. My code is below if anyone could help. I'm using the Entity Framework if that makes a difference. [AspNetCompatibilityRequirements(RequirementsMode = AspNetCompatibilityRequirementsMode.Allowed)] public class MessageService {//: IMessageService { /// <summary> /// Sends a new message. /// </summary> /// <param name="recipientUsername">The recipient username.</param> /// <param name="subject">The subject.</param> /// <param name="messageBody">The message body.</param> [OperationContract] public void SendMessageByDetails(string recipientUsername, string subject, string messageBody) { MessageDAL.SendMessage(recipientUsername, subject, messageBody); } /// <summary> /// Sends a new message. /// </summary> /// <param name="msg">The message to send.</param> [OperationContract] public void SendMessage(Message msg) { MessageDAL.SendMessage(msg); } }

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• Dynamic Linq Library Guid exceptions

  - by Adan

  I am having a problem with the Dynamic Linq Library. I get a the following error "ParserException was unhandled by user code ')" or ','". I have a Dicitionary and I want to create a query based on this dictionary. So I loop through my dictionary and append to a string builder "PersonId = (GUID FROM DICTIONARY). I think the problem is were I append to PersonId for some reason I can't seem to convert my string guid to a Guid so the dynamic library don't crash. I have tried this to convert my string guid to a guid, but no luck. query.Append("(PersonId = Guid(" + person.Key + ")"); query.Append("(PersonId = " + person.Key + ")"); I am using VS 2010 RTM and RIA Services as well as the Entity Framework 4. //This is the loop I use foreach (KeyValuePair<Guid, PersonDetails> person in personsDetails) { if ((person.Value as PersonDetails).IsExchangeChecked) { query.Append("(PersonId = Guid.Parse(" + person.Key + ")"); } } //Domain service call var query = this.ObjectContext.Persons.Where(DynamicExpression.ParseLambda<Person, bool>(persons)); Please help, and if you know of a better way of doing this I am open to suggestions.

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• What is the best method for updating all changed data in EF 4?

  - by Soul_Master

  I try to create some method that can update any changed data from changed Data object (this object is generated by ASP.NET MVC) to old Data object (this object is retrieved from current data in DBMS) like the following code. public static bool UpdateSomeData(SomeEntities context, SomeModelType changedData) { var oldData = GetSomeModelTypeById(context, changedData.ID); UpdateModel(oldData, changedData); return context.SaveChanges() > 0; } I try to create method for saving any changed data without affects other unchanged data like the following source code. public static void UpdateModel<TModel>(TModel oldData, TModel changedData) { foreach (var pi in typeof(TModel).GetProperties() .Where ( // Ignore Change ID property for security reason x => x.Name.ToUpper() != "ID" && x.CanRead && x.CanWrite && ( // It must be primitive type or Guid x.PropertyType.FullName.StartsWith("System") && !x.PropertyType.FullName.StartsWith("System.Collection") && !x.PropertyType.FullName.StartsWith("System.Data.Entity.DynamicProxies") ) ) { var oldValue = pi.GetValue(oldData, null); var newValue = pi.GetValue(changedData, null); if (!oldValue.Equals(newValue)) { pi.SetValue(oldData, newValue, null); } } } I am not sure about the above method because it is so ugly method for updating data. From recent bug, it realizes me that if you update some property like Navigation Properties (related data from other table), it will remove current record from database. I don't understand why it happened. But it is very dangerous for me. So, do you have any idea for this question to ensure me about updating data from ASP.NET MVC? Thanks,

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• How to return all records and whether a related record exists?

  - by David Glenn

  Using Entity Framework 4 CTP5 I have a basic model and a basic DbContext that works public class Customer { public int CustomerId { get; set; } public int Name { get; set; } //... public ICollection<Address> Addresses { get; set; } public bool HasAddress { get { return Addresses.Count > 0; } } } public class Address { public int AddressId { get; set; } public string StreetLine1 { get; set; } //.... public Customer Customer { get; set; } } How can I query my DbContext to return all customers and whether they have an address? A customer can have multiple addresses and I don't want to return all the addresses for each customer when I am only interested in whether they have an address or not. I use context.Customers.Include(c => c.Addresses) but that returns all addresses for each customer

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• EF 4 Self Tracking Entities does not work as expected.

  - by ashraf

  I am using EF4 Self Tracking Entities (VS2010 Beta 2 CTP 2 plus new T4 generator). But when I try to update entity information it does not update to database as expected. I setup 2 service calls. one for GetResource(int id) which return a resource object. the second call is SaveResource(Resource res); here is the code. public Resource GetResource(int id) { using (var dc = new MyEntities()) { return dc.Resources.Where(d => d.ResourceId == id).SingleOrDefault(); } } public void SaveResource(Resource res) { using (var dc = new MyEntities()) { dc.Resources.ApplyChanges(res); dc.SaveChanges(); // Nothing save to database. } } //Windows Console Client Calls var res = service.GetResource(1); res.Description = "New Change"; // Not updating... service.SaveResource(res); // does not change anything. It seems to me that ChangeTracker.State is always show as "Unchanged". anything wrong in this code?

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• Multi threading in WCF RIA Services

  - by synergetic

  I use WCF RIA Services to update customer database. In domain service: public void UpdateCustomer(Customer customer) { this.ObjectContext.Customers.AttachAsModified(customer); syncCustomer(customer); } After update, a database trigger launches and depending on the columns updated it may insert a new record in CustomerChange table. syncCustomer(customer) method is executed to check for a new record in the CustomerChange table and if found it will create a text file which contains customer information and forwards that file to external system for import. Now this synchronization may take a time so I wanted to execute it in different thread. So: private void syncCustomer(Customer customer) { this.ObjectContext.SaveChanges(); new Thread(() => syncCustomerInfo(customer.CustomerID)) { IsBackground = true }.Start(); } private void syncCustomerInfo(int customerID) { //Thread.Sleep(2000); //does real job here ... ... } The problem is in most cases syncCustomerInfo method cannot find any new CustomerChange record even if it was definitely there. If I force thread sleep then it finds a new record. I also looked Entity Framework events but the only event provided by object context is SavingChanges which occur before changes are saved. Please suggest me what else to try.

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• Linq to Entities custom ordering via position mapping table

  - by Bigfellahull

  Hi, I have a news table and I would like to implement custom ordering. I have done this before via a positional mapping table which has newsIds and a position. I then LEFT OUTER JOIN the position table ON news.newsId = position.itemId with a select case statement CASE WHEN [position] IS NULL THEN 9999 ELSE [position] END and order by position asc, articleDate desc. Now I am trying to do the same with Linq to Entities. I have set up my tables with a PK, FK relationship so that my News object has an Entity Collection of positions. Now comes the bit I can't work out. How to implement the LEFT OUTER JOIN. I have so far: var query = SelectMany (n => n.Positions, (n, s) => new { n, s }) .OrderBy(x => x.s.position) .ThenByDescending(x => x.n.articleDate) .Select(x => x.n); This kinda works. However this uses a INNER JOIN so not what I am after. I had another idea: ret = ret.OrderBy(n => n.ShufflePositions.Select(s => s.position)); However I get the error DbSortClause expressions must have a type that is order comparable. I also tried ret = ret.GroupJoin(tse.ShufflePositions, n => n.id, s => s.itemId, (n, s) => new { n, s }) .OrderBy(x => x.s.Select(z => z.position)) .ThenByDescending(x => x.n.articleDate) .Select(x => x.n); but I get the same error! If anyone can help me out, it would be much appreciated!

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• EF/LINQ: Where() against a property of a subtype

  - by ladenedge

  I have a set of POCOs, all of which implement the following simple interface: interface IIdObject { int Id { get; set; } } A subset of these POCOs implement this additional interface: interface IDeletableObject : IIdObject { bool IsDeleted { get; set; } } I have a repository hierarchy that looks something like this: IRepository<T <: BasicRepository<T <: ValidatingRepository<T (where T is IIdObject) I'm trying to add a FilteringRepository to the hierarchy such that all of the POCOs that implement IDeletableObject have a Where(p => p.IsDeleted == false) filter applied before any other queries take place. My goal is to avoid duplicating the hierarchy solely for IDeletableObjects. My first attempt looked like this: public override IQueryable<T> Query() { return base.Query().Where(t => ((IDeletableObject)t).IsDeleted == false); } This works well with LINQ to Objects, but when I switch to an EF backend I get: "LINQ to Entities only supports casting Entity Data Model primitive types." I went on to try some fancier parameterized solutions, but they ultimately failed because I couldn't make T covariant in the following case for some reason I don't quite understand: interface IQueryFilter<out T> // error { Expression<Func<T, bool>> GetFilter(); } I'd be happy to go into more detail on my more complicated solutions if it would help, but I think I'll stop here for now in hope that someone might have an idea for me to try. Thanks very much in advance!

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• Using ADO.NET Entities LINQ Provider to model complex SQL Queries?

  - by Ivan Zlatanov

  What I find really powerful in ADO.NET Entities or LINQ to SQL, is the ability to model complex queries. I really don't need the mappings that Entities or LINQ to SQL are doing for me - I just need the ability to model complex expressions that can be translated into T-SQL. My question is - am I abusing too much? Can I use the Entity Framework for modeling queries and just that? Should I? I know I can write my own custom LINQ to SQL provider, but that is just not possible to handle in the time spans I have. What is the best approach to model complex T-SQL queries? How do you handle conditional group byes, orders, joins, unions etc in the OOP world? Using StringBuilders for this kind of job feels too ugly and harder to maintain given the possibilities we have with Expression Trees. When I use StringBuilder to model a complex SQL Query I feel kind of guilty! I feel the same way as when I have to hard code any number into my code that is different than 0 or 1. Feeling that makes you ask yourself if there is a better and cleaner way of doing it... I must mention that I am using C# 4.0, but I am not specifically looking for an answer in this language, but rather in the domain of CLR 4.

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• edmx - The operation could not be completed - When adding Inheritance

  - by vdh_ant

  Hey guys I have an edmx model which I have draged 2 tables onto - One called 'File' and the other 'ApplicaitonFile'. These two tables have a 1 to 1 relationship in the database. If I stop here everything works fine. But in my model, I want 'ApplicaitonFile' to inherit from 'File'. So I delete the 1 to 1 relationship then configure 'ApplicaitonFile' from 'File' and then remove the FileId from 'ApplicaitonFile' which was the primary key. (Note I am following the instructions from here). If I leave the model open at this point everything is fine, but as soon as I close it, if I try and reopen it again I get the following error "The operation could not be completed". I have been searching for a solution and found this - http://stackoverflow.com/questions/944050/entity-model-does-not-load but as far as I can tell I don't have a duplicate InheritanceConnectors (although I don't know exactly what I'm looking for but I can't see anything out of the ordinary - like 2 connectors with the same name) and the relationship I originally have is a 1 to 1 not a 1 to 0..1 Any ideas??? this is driving me crazy...

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• Parallel.Foreach loop creating multiple db connections throws connection errors?

  - by shawn.mek

  Login failed. The login is from an untrusted domain and cannot be used with Windows authentication I wanted to get my code running in parallel, so I changed my foreach loop to a parallel foreach loop. It seemed simple enough. Each loop connects to the database, looks up some stuff, performs some logic, adds some stuff, closes the connection. But I get the above error? I'm using my local sql server and entity framework (each loop uses it's own context). Is there some problem with connecting multiple times using the same local login or something? How did I get around this? I have (before trying to covert to a parallel.foreach loop) split my list of objects that I am foreach looping through into four groups (separate csv files) and run four concurrent instances of my program (which ran faster overall than just one, thus the idea for parallel). So it seems connecting to the db shouldn't be a problem? Any ideas? EDIT: Here's before var gtgGenerator = new CustomGtgGenerator(); var connectionString = ConfigurationManager.ConnectionStrings["BioEntities"].ConnectionString; var allAccessionsFromObs = _GetAccessionListFromDataFiles(collectionId); ForEach(cloneIdAndAccessions in allAccessionsFromObs) DoWork(gtgGenerator, taxonId, organismId, cloneIdAndAccessions, connectionString)); after var gtgGenerator = new CustomGtgGenerator(); var connectionString = ConfigurationManager.ConnectionStrings["BioEntities"].ConnectionString; var allAccessionsFromObs = _GetAccessionListFromDataFiles(collectionId); Parallel.ForEach(allAccessionsFromObs, cloneIdAndAccessions => DoWork(gtgGenerator, taxonId, organismId, cloneIdAndAccessions, connectionString)); Inside the DoWork I use the BioEntities using (var bioEntities = new BioEntities(connectionString)) {...}

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• Effective books for learning the intricacies of business application development?

  - by OffApps Cory

  I am a self taught "developer". I use the term loosely because I only know enough to make myself dangerous. I have no theory background, and I only pick up things to get this little tool to work or make that control do what I want. That said, I am looking for some reading material that explains some of the theory behind application development especially from a business standpoint. Really I need to understand what all of these terms that float around really talk about. Business Logic Layer, UI abstraction level and all that. Anyone got a reading list that they feel helped them understand this stuff? I know how to code stuff up so that it works. It is not pretty mostly because I don't know the elegant way of doing it, and it is not planned out very well (I also don't know how to plan an application). Any help would be appreciated. I have read a number of books on what I thought was the subject, but they all seem to rehash basic coding and what-not. This doesn't have to be specific to VB.NET or WPF (or Entity Framework) but anything with those items would be quite helpful.

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• Circular Reference exception with JSON Serialisation with MVC3 and EF4 CTP5w

  - by nakchak

  Hi I'm having problems with a circular reference when i try and serialise an object returned via EF4 CTP5. Im using the code first approach and simple poco's for my model. I have added [ScriptIgnore] attributes to any properties that provide a back references to an object and annoyingly every seems to work fine if i manually instantiate the poco's, i.e. they serialise to JSON fine, and the scriptignore attribute is acknowledged. However when i try and serialise an object returned from the DAL i get the circular reference exception "A circular reference was detected while serializing an object of type 'System.Data.Entity.DynamicProxies.xxxx'" I have tried several ways of retreiving the data but they all get stuck with this error: public JsonResult GetTimeSlot(int id) { TimeSlotDao tsDao = new TimeSlotDao(); TimeSlot ts = tsDao.GetById(id); return Json(ts); } The method below works slightly better as rather than the timeslot dynamic proxied object causing the circular refference its the appointment object. public JsonResult GetTimeSlot(int id) { TimeSlotDao tsDao = new TimeSlotDao(); var ts = from t in tsDao.GetQueryable() where t.Id == id select new {t.Id, t.StartTime, t.Available, t.Appointment}; return Json(ts); } Any ideas or solutions to this problem? Update I would prefer to use the out of the box serialiser if possible although Json.Net via nuget is ok as an alternative i would hope its possible to use it as I intended as well...

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• Detaching all entities of T to get fresh data

  - by Goran

  Lets take an example where there are two type of entites loaded: Product and Category, Product.CategoryId - Category.Id. We have available CRUD operations on products (not Categories). If on another screen Categories are updated (or from another user in the network), we would like to be able to reload the Categories, while preserving the context we currently use, since we could be in the middle of editing data, and we do not want changes to be lost (and we cannot depend on saving, since we have incomplete data). Since there is no easy way to tell EF to get fresh data (added, removed and modified), we thought of twp possible ways: 1) Getting products attached to context, and categories detached from context. This would mean that we loose the ability to access Product.Category.Name, which we do sometimes require, so we would need to manually resolve it (example when printing data). 2) detaching / attaching all Categories from current context. Context.ChangeTracker.Entries().Where(x => x.Entity.GetType() == typeof(T)).ForEach(x => x.State = EntityState.Detached); And then reload the categories, which will get fresh data. Do you find any problem with this second approach? We understand that this will require all constraints to be put on foreign keys, and not navigation properties, since when detaching all Categories, Product.Category navigation properties would be reset to null also. Also, there could be a potential performance problem, which we did not test, since there could be couple of thousand products loaded, and all would need to resolve navigation property when reloading. Which of the two do you prefer, and is there a better way (EF6 + .NET 4.0)?

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