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• Replacing NHibernate with LINQ to SQL or LINQ to EF

  - by masoud ramezani

  We have a great project that use NHibernate as ORM. We want to migrate to L2S or L2EF. Can we do everything that we do by NHibernate? Do you propose us that doing this work? What is the advantages and disadvantages of this work?

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• IQueryable and lazy loading

  - by Nelson

  I'm having a hard time determining the best way to handle this... With Entity Framework (and L2S), LINQ queries return IQueryable. I have read various opinions on whether the DAL/BLL should return IQueryable, IEnumerable or IList. Assuming we go with IList, then the query is run immediately and that control is not passed on to the next layer. This makes it easier to unit test, etc. You lose the ability to refine the query at higher levels, but you could simply create another method that allows you to refine the query and still return IList. And there are many more pros/cons. So far so good. Now comes Entity Framework and lazy loading. I am using POCO objects with proxies in .NET 4/VS 2010. In the presentation layer I do: foreach (Order order in bll.GetOrders()) { foreach (OrderLine orderLine in order.OrderLines) { // Do something } } In this case, GetOrders() returns IList so it executes immediately before returning to the PL. But in the next foreach, you have lazy loading which executes multiple SQL queries as it gets all the OrderLines. So basically, the PL is running SQL queries "on demand" in the wrong layer. Is there any sensible way to avoid this? I could turn lazy loading off, but then what's the point of having this "feature" that everyone was complaining EF1 didn't have? And I'll admit it is very useful in many scenarios. So I see several options: Somehow remove all associations in the entities and add methods to return them. This goes against the default EF behavior/code generation and makes it harder to do some composite (multiple entity) LINQ queries. It seems like a step backwards. I vote no. If we have lazy loading anyway which makes it hard to unit test, then go all the way and return IQueryable. You'll have more control farther up the layers. I still don't think this is a good option because IQueryable ties you to L2S, L2E, or your own full implementation of IQueryable. Lazy loading may run queries "on demand", but doesn't tie you to any specific interface. I vote no. Turn off lazy loading. You'll have to handle your associations manually. This could be with eager loading's .Include(). I vote yes in some specific cases. Keep IList and lazy loading. I vote yes in many cases, only due to the troubles with the others. Any other options or suggestions? I haven't found an option that really convinces me.

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• Weird "Designer1.cs" files created

  - by Neil Barnwell

  How does visual studio link files to their corresponding designer.cs files? I have a strange situation that's occurred with both the DataSet designer and also the L2S DBML designer where it's ignoring the DataSet.Designer.cs and has created and used a DataSet.Designer1.cs instead. How can I switch it back?

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• Linq to Sql get SqlCommand when stored procedure execution fails

  - by Tim Mahy

  Hi all, currently I'm assigning a TextWriter to the Log property of my Linq to Sql data context (per request instancing) and write this to my logging when an exception is thrown while executing a stored procedure (is strongly typed mapped in the context, so not executing a custom command) however when using ADO.NET we normally inspect the SqlCommand upon unhandled exception to read out the parameters and log them is it possible to access the SqlCommand that was used for executing a Stored Procedure in L2S so we can reuse that existing logging component? This would be far nicer than the current Log TextWriter solution.... greetings, Tim

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• Arranging VS2008 generated LinqToSql/EntityFramework data models/contexts in assemblies.

  - by JMSA

  What pattern should I use for data-access in case of VS2008 generated L2s or EF DataModels? Repository-pattern or what? As we know VS2008 generates Data-Models and DataContexts/ObjectContexts in the same file, then, how should I arrange my VS2008 assemblies in my VS2008 solution to achieve a layered design? If I use repository pattern, how should I arrange my assemblies in the VS2008 solution (as Data-Models and Data/Object-Contexts are stored in the same file...)? Any web/example link would be appreciated.

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• How do I cache query results using LINQ?

  - by Vince

  Hi, Is there any way to cache LINQ to SQL queries by looking at the parameters that were previously passed and bypass the database all together? I know L2S caches some database calls, but I'm looking for a permanant solution as in, even if the applciation restarts, that cache reloads and never asks the database again. Are there any frameworks for C#?

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• DataObjects.NET: a good (flawless, documented, support) ORM?

  - by David_CSharp

  I am looking for ORM frameworks, came along to NHibernate, Genome, L2S, Entity Framework and now the DataObjects.NET.. So far a I read the documentation it seems pretty cabable, but have you ever tried this ORM? Any issues/bugs with DO.NET would be approciated :)

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• Nested/child collections filtering in Entity Framework (ver. 1 or 4)

  - by gius

  How to filter nested/child collections of entities when including them in EF? Example: Let's have standard Customer-Orders association. How to load all customers and include only their last three orders in their Orders collection? Is there something like AssociateWith function from L2S for EF?

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• LINQ to SQL and missing Many to Many EntityRefs

  - by Rick Strahl

  Ran into an odd behavior today with a many to many mapping of one of my tables in LINQ to SQL. Many to many mappings aren’t transparent in LINQ to SQL and it maps the link table the same way the SQL schema has it when creating one. In other words LINQ to SQL isn’t smart about many to many mappings and just treats it like the 3 underlying tables that make up the many to many relationship. Iain Galloway has a nice blog entry about Many to Many relationships in LINQ to SQL. I can live with that – it’s not really difficult to deal with this arrangement once mapped, especially when reading data back. Writing is a little more difficult as you do have to insert into two entities for new records, but nothing that can’t be handled in a small business object method with a few lines of code. When I created a database I’ve been using to experiment around with various different OR/Ms recently I found that for some reason LINQ to SQL was completely failing to map even to the linking table. As it turns out there’s a good reason why it fails, can you spot it below? (read on :-}) Here is the original database layout: There’s an items table, a category table and a link table that holds only the foreign keys to the Items and Category tables for a typical M->M relationship. When these three tables are imported into the model the *look* correct – I do get the relationships added (after modifying the entity names to strip the prefix): The relationship looks perfectly fine, both in the designer as well as in the XML document: <Table Name="dbo.wws_Item_Categories" Member="ItemCategories"> <Type Name="ItemCategory"> <Column Name="ItemId" Type="System.Guid" DbType="uniqueidentifier NOT NULL" CanBeNull="false" /> <Column Name="CategoryId" Type="System.Guid" DbType="uniqueidentifier NOT NULL" CanBeNull="false" /> <Association Name="ItemCategory_Category" Member="Categories" ThisKey="CategoryId" OtherKey="Id" Type="Category" /> <Association Name="Item_ItemCategory" Member="Item" ThisKey="ItemId" OtherKey="Id" Type="Item" IsForeignKey="true" /> </Type> </Table> <Table Name="dbo.wws_Categories" Member="Categories"> <Type Name="Category"> <Column Name="Id" Type="System.Guid" DbType="UniqueIdentifier NOT NULL" IsPrimaryKey="true" IsDbGenerated="true" CanBeNull="false" /> <Column Name="ParentId" Type="System.Guid" DbType="UniqueIdentifier" CanBeNull="true" /> <Column Name="CategoryName" Type="System.String" DbType="NVarChar(150)" CanBeNull="true" /> <Column Name="CategoryDescription" Type="System.String" DbType="NVarChar(MAX)" CanBeNull="true" /> <Column Name="tstamp" AccessModifier="Internal" Type="System.Data.Linq.Binary" DbType="rowversion" CanBeNull="true" IsVersion="true" /> <Association Name="ItemCategory_Category" Member="ItemCategory" ThisKey="Id" OtherKey="CategoryId" Type="ItemCategory" IsForeignKey="true" /> </Type> </Table> However when looking at the code generated these navigation properties (also on Item) are completely missing: [global::System.Data.Linq.Mapping.TableAttribute(Name="dbo.wws_Item_Categories")] [global::System.Runtime.Serialization.DataContractAttribute()] public partial class ItemCategory : Westwind.BusinessFramework.EntityBase { private System.Guid _ItemId; private System.Guid _CategoryId; public ItemCategory() { } [global::System.Data.Linq.Mapping.ColumnAttribute(Storage="_ItemId", DbType="uniqueidentifier NOT NULL")] [global::System.Runtime.Serialization.DataMemberAttribute(Order=1)] public System.Guid ItemId { get { return this._ItemId; } set { if ((this._ItemId != value)) { this._ItemId = value; } } } [global::System.Data.Linq.Mapping.ColumnAttribute(Storage="_CategoryId", DbType="uniqueidentifier NOT NULL")] [global::System.Runtime.Serialization.DataMemberAttribute(Order=2)] public System.Guid CategoryId { get { return this._CategoryId; } set { if ((this._CategoryId != value)) { this._CategoryId = value; } } } } Notice that the Item and Category association properties which should be EntityRef properties are completely missing. They’re there in the model, but the generated code – not so much. So what’s the problem here? The problem – it appears – is that LINQ to SQL requires primary keys on all entities it tracks. In order to support tracking – even of the link table entity – the link table requires a primary key. Real obvious ain’t it, especially since the designer happily lets you import the table and even shows the relationship and implicitly the related properties. Adding an Id field as a Pk to the database and then importing results in this model layout: which properly generates the Item and Category properties into the link entity. It’s ironic that LINQ to SQL *requires* the PK in the middle – the Entity Framework requires that a link table have *only* the two foreign key fields in a table in order to recognize a many to many relation. EF actually handles the M->M relation directly without the intermediate link entity unlike LINQ to SQL. [updated from comments – 12/24/2009] Another approach is to set up both ItemId and CategoryId in the database which shows up in LINQ to SQL like this: This also work in creating the Category and Item fields in the ItemCategory entity. Ultimately this is probably the best approach as it also guarantees uniqueness of the keys and so helps in database integrity. It took me a while to figure out WTF was going on here – lulled by the designer to think that the properties should be when they were not. It’s actually a well documented feature of L2S that each entity in the model requires a Pk but of course that’s easy to miss when the model viewer shows it to you and even the underlying XML model shows the Associations properly. This is one of the issue with L2S of course – you have to play by its rules and once you hit one of those rules there’s no way around them – you’re stuck with what it requires which in this case meant changing the database.© Rick Strahl, West Wind Technologies, 2005-2010Posted in ADO.NET  LINQ  

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• Best Practices for MVC Architecture

  - by Mystere Man

  There are a number of questions on StackOverflow regard MVC best practices, but most of those seem to revolve around things like using Dependancy Injection, or creating helper functions, or do's and don'ts of what to do in views and controllers. My question is more about how to architect an MVC application. For example, we are encouraged to use DI with the Repository pattern to decouple data access from the controller, however very little is said on HOW to do that specifically for MVC. Where would we place the Repository classes, for instance? They don't seem to be model related specifically, since the model should likewise be relatively decoupled from the actual data access technologies. A second question involves how to structure the layers or tiers. Most example applications (Nerd dinner, Music Store, etc..) all seem to use a single tier, 2 layer approach (not counting tests) that typically has controllers directly calling L2S or EF code. If I want to create a multi-tier/layer aplication what are some of the best practices there in regards to MVC? This question is one-part standard q-a, but another part best-practices, so it could go either here or programmers.se, I am marking it CW. If you feel it would be better suited to programmers.se then it can be migrated. EDIT: What happened to the Community Wiki option? It seems to be gone.

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• Sync Framework, Local Database Cache, and my DAL

  - by Refracted Paladin

  I am creating a WPF app that needs to allow users to work in a temporary disconnected state and I plan to use a Local Database Cache. My question's are about my data access layer. Do you typically create the whole DAL to point at the Cache or both and create a switching mechanism? Is Entity's a good way to go for my DAL against the Cache? I am used to L2S but my understanding is that I can't use that against SQLCE, correct? Thanks! PS: Any good resources out there for using Sync, Linq, and WPF? Tutorials, videos, etc?

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• how to generate dbml file from Sybase database?

  - by 5YrsLaterDBA

  I think we may have trouble with our existing project. For some reasons we have to switch from SQL Server to Sybase SQL Anywhere 11. now we trying to find a way continue use our existing LINQ code. We wish we can still use L2S? If cannot, we wish we can use L2E, then we have to change to ADO. how to generate dbml file from Sybase Anywhere 11? after that can we use sqlmetal to generate .cs files?

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• Sync Framework,LINQ, and my DAL

  - by Refracted Paladin

  I am creating a WPF app that needs to allow users to work in a temporary disconnected state and I plan to use a Local Database Cache. My question's are about my data access layer. Do you typically create the whole DAL to point at the Cache or both and create a switching mechanism? Is Entity's a good way to go for my DAL against the Cache? I am used to L2S but my understanding is that I can't use that against SQLCE, correct? Thanks! PS: Any good resources out there for using Sync, Linq, and WPF ALL TOGETHER? Tutorials, videos, etc?

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• Liqn to sql null-able value in query

  - by msony

  I need get all items what have no categories int? categoryId = null; var items=db.Items.Where(x=>x.CategoryId==categoryId); this code generate in where: where CategoryId=null instead of where CategoryId is null ok, when i write var items=db.Items.Where(x=>x.CategoryId==null); in my sql profiler it works: where CategoryId is null BUT when i do this HACK it doesn't: var items=db.Items.Where(x=>x.CategoryId==(categoryId.HasValue ? categoryId : null)); so what's the problem? is there by in L2S?

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• ASP.NET MVC- Bizarre problem - suddennly lost all LINQTO SQL data context objects

  - by MikeD

  I was making an edit to a long existing project. Specifically I added some fields to a table and had to delete the table from the LINQTOSQL designer and re-add it. doesn't Also had to do the same for a view. Mode some other code changes and went to build . Now my project won't build because it can't resolve any of the data context objects (all tables and views) in my code. I don't know what I did or how this happeened. I have many tables and views in the project's L2S data context so I don't wont to try and do over. Please any suggestions on how to resolve this problem are greatly appreciated. Desparate! The error messages I am getting are the familiar The type or namespace name 'equipment' could not be found (are you missing a using directive or an assembly reference?)

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• How do I improve the efficiency of the queries executed by this generic Linq-to-SQL data access clas

  - by Lee D

  Hi all, I have a class which provides generic access to LINQ to SQL entities, for example: class LinqProvider<T> //where T is a L2S entity class { DataContext context; public virtual IEnumerable<T> GetAll() { return context.GetTable<T>(); } public virtual T Single(Func<T, bool> condition) { return context.GetTable<T>().SingleOrDefault(condition); } } From the front end, both of these methods appear to work as you would expect. However, when I run a trace in SQL profiler, the Single method is executing what amounts to a SELECT * FROM [Table], and then returning the single entity that meets the given condition. Obviously this is inefficient, and is being caused by GetTable() returning all rows. My question is, how do I get the query executed by the Single() method to take the form SELECT * FROM [Table] WHERE [condition], rather than selecting all rows then filtering out all but one? Is it possible in this context? Any help appreciated, Lee

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• Linq to Entities performance within ASP.NET Development Server

  - by tster

  I've been evaluating linq to entities and linq to SQL for a project. Obviously each has its own advantages and disadvantages which have been discussed plenty of times here. However, One thing I am seeing with L2E is kind of odd. Using L2S, when using the ASP.NET Development Server, the performance is a little slower for my web service calls. I'm looking at 300ms vs. 250 ms. However, when using L2E, when using ASP.NET Dev Server, the performance is awful. I'm talking 1,250 ms vs. 220 ms. I know I should probably just use local IIS for development, but I'm curious if anyone else has seen this, or knows what is causing it.

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• Possible to use Tables of same type in Linq to SQL?

  - by Schneider

  Lets say I've got an object model, where I have many collections of the same type. For example something like class StockMarketData { List<SummaryData> WeeklySummary; List<SummaryData> MonthlySummary; } class SummaryData { DateTime DateTime {get; set;} double Value {get; set;} } Those lists will map onto database tables. If you actually use L2S to generate a model from the database you will get something like: class StockMarketData { List<WeeklySummaryData> WeeklySummary; List<MonthlySummaryData> MonthlySummary; } Even though WeeklySummaryData and MonthlySummaryData have the same shape. Is it possible for Linq to SQL to create tables from a database of summary data, but get each table to contain the same type (such as shown in the top example).

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• Proper way to structure a Sync Framework DAL

  - by Refracted Paladin

  I am creating a WPF app that needs to allow users to work in a temporary disconnected state and I plan to use a Local Database Cache. My question's are about my data access layer. Do you typically create the whole DAL to point at the Cache or both and create a switching mechanism? Is Entity's a good way to go for my DAL against the Cache? I am used to L2S but my understanding is that I can't use that against SQLCE, correct? Thanks! PS: Any good resources out there for using Sync, Linq, and WPF ALL TOGETHER? Tutorials, videos, etc?

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• How to use LINQ to SQL to create ranked search results?

  - by quakkels

  I am looking for a way to use l2s to return ranked result based on keywords. I would like to take a keyword and be able to search the table for that keyword using .contains(). The trick that I haven't been able to figure out is how to get a count of how many times that keyqord appears, and then .OrderByDescending() based on that count. So if i had some thing like: string keyword = "SomeKeyword"; IQueryable<Article> searchResults = from a in GenesisRepository.Article where a.Body.Contains(keyword) select a; What is the best way to order searchResults based on the number of times keyword appears in a.Body? Thanks for any help.

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• Entity Framework (4.0) how to exclude a related table.

  - by Kohan

  I have just updated to using EF 4.0 where before i was using Linq 2 SQL. I have a query: var UserList = this.repository.GetUsers(); return Json(UserList, JsonRequestBehavior.AllowGet); This was generating an error: "A circular reference was detected while serializing an object of type" This prompted this code which worked fine in L2S: var UserList = this.repository.GetUsers(); foreach (User u in UserList){ u.Subscriptions = null; } return Json(UserList, JsonRequestBehavior.AllowGet); How can i stop EF from looking into the Subscriptions table, i just want the Userlist, none of the related properties and the above example does not seem to work for this. Cheers, Kohan

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• Linq to SQL inheritance and Table per Class - approach needed for multiple roles

  - by Ash Machine

  I am using L2S and an inheritance model for mapping Persons against certain roles. Guy Burstein's excellent blog post explains how to accomplish this: http://blogs.microsoft.co.il/blogs/bursteg/archive/2007/10/01/linq-to-sql-inheritance.aspx However, I have a specific case where a Person has multiple roles. For example 'Jane Doe' is a Contact and a Programmer. In this model, she would need two rows in the People table, one as Contact (PersonType = 1) and one as Programmer (PersonType = 3). If she changes her last name, and that update happens in her role as Contact, I would need to change all instances of 'Jane Doe' to reflect the name change everywhere. What sort of best approach (improved data structure) could be used to change last name within all roles? Finally, I am hoping to avoid overriding each general form update events to include all instances, but that may be the only way. Any suggestions or approaches appreciated.

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• Linq to Sql query reuse

  - by UserControl

  Let's say we have a view V1 and V2 that is declared like: create view V2 as select V1.*, V2.C1, V2.C2, V2.C3 from V1 join V2 on V1.Key = V2.Key where bla-bla So V2 narrows down the result set of V1 and adds some joins. And there is a retrieval routine in C# IEnumerable<V1> GetData(MyFilter filter, MySortOrder order) {} I want to reuse with V2. Is it possible without performing joins in L2S rather than in database? Should i manually create a base class in the database context or something?

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• When does the DataContext will open a connection to the DB?

  - by Eran Betzalel

  I am using L2S to access my MSSQL 2008 Express server. I would like to know when the DataContext will open a connection to the DB? and will it close the connection right after it opened it? For example: var dc = new TestDB(); // connection opened and closed? dc.SomeTable.InsertOnSubmit(obj); // connection opened and closed? foreach(var obj in dc.SomeTable.AsEnumerable()) // connection opened and closed? { ... // connection opened and closed? } dc.SubmitChanges(); // connection opened and closed?

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• Creating a dynamic linq query

  - by Bas

  I have the following query: from p in dataContext.Repository<IPerson>() join spp1 in dataContext.Repository<ISportsPerPerson>() on p.Id equals spp1.PersonId join s1 in dataContext.Repository<ISports>() on spp1.SportsId equals s1.Id join spp2 in dataContext.Repository<ISportsPerPerson>() on p.Id equals spp2.PersonId join s2 in dataContext.Repository<ISports>() on spp2.SportsId equals s2.Id where s1.Name == "Soccer" && s2.Name == "Tennis" select new { p.Id }; It selects all the person who play Soccer and Tennis. On runtime the user can select other tags to add to the query, for instance: "Hockey". now my question is, how could I dynamically add "Hockey" to the query? If "Hockey" is added to the query, it would look like this: from p in dataContext.Repository<IPerson>() join spp1 in dataContext.Repository<ISportsPerPerson>() on p.Id equals spp1.PersonId join s1 in dataContext.Repository<ISports>() on spp1.SportsId equals s1.Id join spp2 in dataContext.Repository<ISportsPerPerson>() on p.Id equals spp2.PersonId join s2 in dataContext.Repository<ISports>() on spp2.SportsId equals s2.Id join spp3 in dataContext.Repository<ISportsPerPerson>() on p.Id equals spp3.PersonId join s3 in dataContext.Repository<ISports>() on spp3.SportsId equals s3.Id where s1.Name == "Soccer" && s2.Name == "Tennis" && s3.Name == "Hockey" select new { p.Id }; It would be preferable if the query is build up dynamically like: private void queryTagBuilder(List<string> tags) { IDataContext dataContext = new LinqToSqlContext(new L2S.DataContext()); foreach(string tag in tags) { //Build the query? } } Anyone has an idea on how to set this up correctly? Thanks in advance!

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