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• Insert record in Linq to Sql

  - by Anders Svensson

  Is this the easiest way to insert a record with Linq to Sql when there's a many-to-many relationship, or is there a better/cleaner way? I wasn't sure why things weren't working at first, but when I added a second SubmitChanges() it worked. Why was this necessary? Would be grateful if someone could clarify this a bit! private void InsertNew() { UserPageDBDataContext context = new UserPageDBDataContext(); User user = new User(); ManyToMany.Model.Page page = new ManyToMany.Model.Page(); user.Name = "Madde Andersson"; page.Url = "anderscom/references"; context.Users.InsertOnSubmit(user); context.Pages.InsertOnSubmit(page); context.SubmitChanges(); UserPage userPage = new UserPage(); userPage.UserID = user.UserID; userPage.PageID = page.PageID; user.UserPages.Add(userPage); context.SubmitChanges(); }

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• Problem with Linq query and date format

  - by Alan T

  Hi All I have a C# console application written using Visual Studio 2008. My system culture is en-GB. I have a Linq query that looks like this: var myDate = "19-May-2010"; var cus = from x in _dataContext.testTable where x.CreateDate == Convert.ToDateTime(myDate) select x; The resulting SQL query generates and error because it returns the dates as "19/05/2010" which it interprets as an incorrect date. For some reason even though my system culture is set to en-GB it looks like it's trying to intrepret it as a en-US date. Any ideas how I get around this? Thanks. Alan T

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• LINQ to remove duplicated property

  - by Shawn Mclean

  I have a LINQ statement like this: var media = (from p in postService.GetMedia(postId) select new { PostId = postId, SynthId = p.SynthId }); There are many(possibly thousands) of records returned with the same SynthId. I want to select one one, any random one. So when I'm finished, media should contain records with distinct SynthId. SynthId can be null, I want all nulls to be in media (the distinct should not affect them). My DAL is EntityFramework, if that will help. How do I accomplish this in the most efficient way?

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• ASP.NET MVC TDD with LINQ and SQL database

  - by dean nolan

  I am trying to start a new MVC project with tests and I thought the best way to go would have 2 databases. 1 for testing against and 1 for when I run the app and use it (also test really as it's not production yet). For the test database I was thinking of putting create table scripts and fill data scripts within the test setup method and then deleting all this in the tear down method. I am going to be using Linq to SQL though and I don't think that will allow me to do this? Will I have to just go the ADO route if I want to do it this way? Or should I just use a mock object and store data as an array or something?. Any tips on best practices? How did Jeff go about doing this for StackOveflow?

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• Make CSV from list of string in LINQ

  - by CmdrTallen

  Hi I would like to take a list collection and generate a single csv line. So take this; List<string> MakeStrings() { List<string> results = new List<string>(); results.add("Bob"); results.add("Nancy"); results.add("Joe"); results.add("Jack"); } string ContactStringsTogether(List<string> parts) { StringBuilder sb = new StringBuilder(); foreach (string part in parts) { if (sb.Length > 0) sb.Append(", "); sb.Append(part); } return sb.ToString(); } This returns "Bob,Nancy,Joe,Jack" Looking for help on the LINQ to do this in a single statement. Thanks!

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• Linq to sql add/update in different methods with different datacontexts

  - by Kurresmack

  I have to methods, Add() and Update() which both create a datacontext and returns the object created/updated. In my unit test I call first Add(), do some stuff and then call Update(). The problem is that Update() fails with the exception: System.Data.Linq.DuplicateKeyException: Cannot add an entity with a key that is already in use.. I understand the issue but want to know what to do about it? I've read a bit about how to handle multiple datacontext objects and from what I've heard this way is OK. I understand that the entity is still attached to the datacontext in Add() but I need to find out how to solve this? Thanks in advance

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• Help with linq to sql compiled query

  - by stackoverflowuser

  Hi I am trying to use compiled query for one of my linq to sql queries. This query contains 5 to 6 joins. I was able to create the compiled query but the issue I am facing is my query needs to check if the key is within a collection of keys passed as input. But compiled queries do not allow passing of collection (since collection can have varying number of items hence not allowed). For instance input to the function is a collection of keys. Say: List<Guid> InputKeys List<SomeClass> output = null; var compiledQuery = CompiledQueries.Compile<DataContext, IQueryable<SomeClass>>( (context) => from a in context.GetTable<A>() where InputKeys.Contains(a.Key) select a); using(var dataContext = new DataContext()) { output = compiledQuery(dataContext).ToList(); } return output; Is there any work around or better way to do the above?

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• ADO.NET Entity Model and LINQ

  - by Richard

  Hi all I'm using an ADO.NET Entity Model which I'm trying to query using LINQ. The problem I'm having is that I can't specify the where clause as I'd like. For instance, consider the following query: AccountsDM db = new AccountsDM(ConfigurationManager.ConnectionStrings["PrimaryEF"].ConnectionString); var accounts = from a in db.Accounts select a; foreach (var account in accounts) { foreach (var ident in account.Identifiers) { if (ident.Identifier == identifier) { // ident.Identifier is what I'd like to be filtering in the WHERE clause below } } } Ideally, I'd like that to become: var accounts = from a in db.Accounts where a.Identifiers.Identifier == identifier select a; I'm guessing I've probably not set up my Entity Model correctly in VS2010. Any advice you can offer would be gratefully received. Thanks, Richard.

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• linq to sql datacontext for a web application

  - by rap-uvic

  Hello, I'm trying to use linq to sql for my project (very short deadline), and I'm kind of in a bind. I don't know the best way to have a data context handy per request thread. I want something like a singleton class from which all my repository classes can access the current data context. However, singleton class is static and is not thread-safe and therefore not suitable for web apps. I want something that would create a data context at the beginning of the request and dispose of it along with the request. Can anyone please share their solution to this problem? I've been searching for a solution and I've found a good post from Rick Strahl : http://www.west-wind.com/weblog/posts/246222.aspx but I don't completely understand his thread-safe or business object approach. If somebody has a simplified version of his thread-safe approach, i'd love to take a look.

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• Linq to sql translation to sql of custom method

  - by DJPB

  hi there is there a way to translate an expression to sql to use with linq to sql? for example I have a method that compares two values example: MyComparer.Compare(value1, value2, ">") return value1 > value2 MyComparer.Compare(value1, value2, "=") return value1 == value2 MyComparer.Compare(value1, value2, "<=") return value1 <= value2 and i would like a query like var list = from i in dataContext.items where MyComparer.Compare(i.value, someValue, "some operator") select ... this won't work because, obviously, MyComparer doesn't translate to sql maybe this is a twisted question, but how can i translate this method to sql or is this possible? tks

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• LINQ To SQL Wildcards

  - by mcass20

  How can I build in wildcards to my LINQ To SQL lambda expression? This is what I have currently: var query = from log in context.Logs select log; foreach (string filter in CustomReport.ExtColsToFilter) { string tempFilter = filter; query = query.Where(Log => Log.FormattedMessage.Contains(tempFilter)); } This works fine up until I try and pass wildcards in the filter string. I'm experimenting with SqlMethods.Like() but to no avail. The filters above look like this: "<key>NID</key><value>mcass</value>". I'd like to be able to pass filters like this: "<key>NID</key><value>%m%</value>"

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• Should methods containing LINQ expressions be tested / mocked?

  - by Phil.Wheeler

  Assuming I have a class with a method that takes a System.Linq.Expressions.Expression as a parameter, how much value is there in unit testing it? public void IEnumerable<T> Find(Expression expression) { return someCollection.Where(expression).ToList(); } Unit testing or mocking these sorts of methods has been a mind-frying experience for me and I'm now at the point where I have to wonder whether it's all just not worth it. How would I unit test this method using some arbitrary expression like List<Animal> = myAnimalRepository.Find(x => x.Species == "Cat");

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• Getting a set of elements using linq

  - by MarceloRamires

  I have the following piece of XML: <xml> <ObsCont xCampo="field1"> <xTexto>example1</xTexto> </ObsCont> <ObsCont xCampo="field2"> <xTexto>example2</xTexto> </ObsCont> <ObsCont xCampo="field3"> <xTexto>example3</xTexto> </ObsCont> </xml> How do I (using linq) get for example what is inside the xTexto tag that has as parent the ObsCont with the xCampo attribute "field2" ? (c#, vb.net, your choice)

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• Binding Linq To Entities query results to a datagridview

  - by Nickson

  I just started playing with Linq to entities in a windows forms application and am not understanding one behavior that looks so simple though. If i type code below, i get ReadOnly records in my dataGridView Dim x = From n in Table1 _ Select n.FirstName, n.LastName, N.Department DataGridView1.DataSource = x But if i type the following code, i get editable rows in my dataGridView Dim x = From n in Table1 _ Select n DataGridView1.DataSource = x So, basically if i specify the column names to select and databind to my DataGridView1, the rows are readonly but if i do not specify the column names and databind to the DataGridView, the rows are editable and i don't understand why.

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• Using LINQ to search a byte array for all subarrays that start/stop with certain byte

  - by Joel B

  I'm dealing with a COM port application and we have a defined variable-length packet structure that I'm talking to a micro-controller with. The packet has delimiters for the start and stop bytes. The trouble is that sometimes the read buffer can contain extraneous characters. It seems like I'll always get the whole packet, just some extra chatter before/after the actual data. So I have a buffer that I append data to whenever new data is received from the COM port. What is the best way to search this buffer for any possible occurrences of my packet? For example: Say my packet delimiter is 0xFF and I have an array as such { 0x00, 0xFF, 0x02, 0xDA, 0xFF, 0x55, 0xFF, 0x04 } How can I create a function/LINQ-statment that returns all subarrays that start and end with the delimiter (almost like a sliding-correlator with wildcards)? The sample would return the following 3 arrays: {0xFF, 0x02, 0xDA, 0xFF}, {0xFF, 0x55, 0xFF}, and {0xFF, 0x02, 0xDA, 0xFF, 0x55, 0xFF}

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• Return nested alias for linq expression

  - by Schotime

  I have the following Linq Expression var tooDeep = shoppers .Where(x => x.Cart.CartSuppliers.First().Name == "Supplier1") .ToList(); I need to turn the name part into the following string. x.Cart.CartSuppliers.Name As part of this I turned the Expression into a string and then split on the . and removed the First() argument. However, when I get to CartSuppliers this returns a Suppliers[] array. Is there a way to get the single type from this. eg. I need to get a Supplier back. Thanks

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• Problem with linq-to-xml

  - by phenevo

  I want by linq save my xml in csv and I have o problem. This bracket are here beacuse without it this code is not displaying (why ? ) bracket results bracket <Countries country="Albania"><Regions region="Centralna Albania"><Provinces province="Durres i okolice"><Cities city="Durres" cityCode="2B66E0ACFAEF78734E3AF1194BFA6F8DEC4C5760"><IndividualFlagsWithForObjects Status="1" /><IndividualFlagsWithForObjects Status="0" /><IndividualFlagsWithForObjects magazyn="2" /></Cities></Provinces></Regions></Countries><Countries .... XDocument loaded = XDocument.Load(@"c:\citiesxml.xml"); // create a writer and open the file TextWriter tw = new StreamWriter("c:\\XmltoCSV.txt"); // Query the data and write out a subset of contacts var contacts = (from c in loaded.Descendants("Countries") select new { Country = (string)c.Element("Country"), Region = (string)c.Element("region"), Province= (string)c.Element("province"), City = (string)c.Element("city"), Hotel = (string)c.Element("hotel") }).ToList(); Problem is that loaded.Descendants("Countries") gives me 45 countries but all fields are null.

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• attaching linq to sql datacontext to httpcontext in business layer

  - by rap-uvic

  Hello all, I need my linq to sql datacontext to be available across my business/data layer for all my repository objects to access. However since this is a web app, I want to create and destroy it per request. I'm wondering if having a singleton class that can lazily create and attach the datacontext to current HttpContext would work. My question is: would the datacontext get disposed automatically when the request ends? Below is the code for what I'm thinking. Would this accomplish my purpose: have a thread-safe datacontext instance that is lazily available and is automatically disposed when the request ends? public class SingletonDC { public static NorthwindDataContext Default { get { NorthwindDataContext defaultInstance = (NorthwindDataContext)System.Web.HttpContext.Current.Items["datacontext"]; if (defaultInstance == null) { defaultInstance = new NorthwindDataContext(); System.Web.HttpContext.Current.Items.Add("datacontext", defaultInstance); } return defaultInstance; } } }

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• LINQ: Dot Notation vs Query Expression

  - by Martín Marconcini

  I am beginning to use LINQ in general (so far toXML and toSQL). I've seen that sometimes there are two or more ways to achieve the same results. Take this simple example, as far as I understand both return exactly the same thing: SomeDataContext dc = new SomeDataContext(); var queue = from q in dc.SomeTable where q.SomeDate <= DateTime.Now && q.Locked != true orderby (q.Priority, q.TimeCreated) select q; var queue2 = dc.SomeTable .Where( q => q.SomeDate <= DateTime.Now && q.Locked != true ) .OrderBy(q => q.Priority) .ThenBy(q => q.TimeCreated); Besides any mistake I may have made in the syntax or a missing parameter or difference, the idea is that there are two ways to express the same thing; I understand that the first method has some limitations and that the "dot notation" is more complete, but besides that, are there any other advantages?

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• How to SET ARITHABORT ON for connections in Linq To SQL

  - by Laurence

  By default, the SQL connection option ARITHABORT is OFF for OLEDB connections, which I assume Linq To SQL is using. However I need it to be ON. The reason is that my DB contains some indexed views, and any insert/update/delete operations against tables that are part of an indexed view fail if the connection does not have ARITHABORT ON. Even selects against the indexed view itself fail if the WITH(NOEXPAND) hint is used (which you have to use in SQL Standard Edition to get the performance benefit of the indexed view). Is there somewhere in the data context I can specify I want this option ON? Or somewhere in code I can do it?? I have managed a clumsy workaround, but I don't like it .... I have to create a stored procedure for every select/insert/update/delete operation, and in this proc first run SET ARITHABORT ON, then exec another proc which contains the actual select/insert/update/delete. In other words the first proc is just a wrapper for the second. It doesn't work to just put SET ARITHABORT ON above the select/insert/update/delete code.

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• LINQ and set difference

  - by Pierre

  I have two collections a and b. I would like to compute the set of items in either a or b, but not in both (a logical exclusive or). With LINQ, I can come up with this: IEnumerable<T> Delta<T>(IEnumerable<T> a, IEnumerable<T> b) { return a.Except (b).Union (b.Except (a)); } I wonder if there are other more efficient or more compact ways of producing the difference between the two collections.

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• How to perform a many-to-many Linq query with Include in the EF.

  - by despart

  Hi, I don't know how to perform this query using Linq and the EF. Imagine I have three tables A, B and C. A and B have a many-to-many relationship. B and C have a 1-to-many relationship. I want to obtain records from B including C but filtering from A's Id. I can get easily the records from B: var b = Context.A.Where(x => x.Id.Equals(aId)).SelectMany(x => x.B); but when I try to include C I don't know how to do it: //This doesn't work var b = Context.A.Where(x => x.Id.Equals(aId)).SelectMany(x => x.B.Include("C")); Also I've tried this with no luck (it is equivalent to the above): //Not working var b = (from a in Context.A.Where(x => x.Id.Equals(aId)) from b in a.B.Include("C") select b); Thanks for your help.

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• Converting SQL statement into Linq

  - by DMan

  I'm trying to convert the following to a LINQ to SQL statement in C#. Can anyone give me a hand? Basically my table keeps record of all history of changes such that the created date max date for each seedlot is the most recent record and the correct one to show. SELECT reports.* FROM [dbo].[Reports] reports WHERE reports.createdDate IN ( SELECT MAX(report_max_dates.createdDate) FROM [dbo].[Reports] report_max_dates GROUP BY report_max_dates.Lot ) So far this is what I have. var result = (from report in db.Reports where report.createdDate == (from report_max in db.Reports group report_max by report_max.Lot into report_max_grouped select report_max_grouped).Max() select report); I can't figure out how to get the MAX dates for all reports and how to do an IN statement on the report.createdDate. Thansk, Dman

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• Use LINQ and lambdas to put string in proper case

  - by Tobias Funke

  I have this function called ProperCase that takes a string, then converts the first letter in each word to uppercase. So ProperCase("john smith") will return "John Smith". Here is the code: public string ProperCase(string input) { var retVal = string.Empty; var words = input.Split(' '); foreach (var word in words) { if (word.Length == 1) { retVal += word.ToUpper(); } else if (word.Length > 1) { retVal += word.Substring(0, 1).ToUpper() + word.Substring(1).ToLower(); } retVal += ' '; } if (retVal.Length > 0) { retVal = retVal.Substring(0, retVal.Length - 1); } return retVal; } This code workds perfectly, but I'm pretty sure I can do it more elegantly with LINQ and lambdas. Can some please show me how?

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• LINQ OrderBy with more than one field

  - by brainimus

  I have a list that I need sorted by two fields. I've tried using OrderBy in LINQ but that only allows me to specify one field. I'm looking for the list to be sorted by the first field and then if there are any duplicates in the first field to sort by the second field. For example I want the results to look like this (sorted by last name then first name). Adams, John Smith, James Smith, Peter Thompson, Fred I've seen that you can use the SQL like syntax to accomplish this but I am looking for a way to do it with the OrderBy method. IList<Person> listOfPeople = /*The list is filled somehow.*/ IEnumerable<Person> sortedListOfPeople = listOfPeople.OrderBy(aPerson => aPerson.LastName, aPerson.FirstName); //This doesn't work.

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