Sql – How to get to the bottom of this Linq to SQL error

linq-to-sql

An attempt has been made to Attach or
Add an entity that is not new, perhaps
having been loaded from another
DataContext. This is not supported.

Having worked with Linq to SQL for some time, I believe that I know about its limitations and that I follow the rules when I write new code. But it is frustrating to get this exception, as there is no indication of which object caused the violation. In complex data manipulation scenarios with multiple DCs, I can only think of trial-and-error to narrow down the possible culprits. Is there a way to find out more?

Best Answer

If you attach an object to your DataContext, it must have been created by you using the new operator. If you read the object from a DataContext, you must save it to the same DataContext.

To alleviate these kinds of problems, I always use a single DataContext, and I do everything on a "unit of work" basis.

Generally speaking, that means that, at any given time, I am reading the records I need, performing work on those records, and saving changes, all in a single unit of work, using a single DataContext. Since it is a unit of work, it doesn't bleed over into other DataContext objects.

If Linq to SQL is fighting you on this, I would examine your architecture and see if the way you are doing it is optimal, especially if you are finding it difficult to identify the object causing the error. In general it is difficult to share objects between DataContexts. You can do it (using things like "attach" and "detach"), but it's a pain in the ass.

Related Solutions

.net – Entity Framework vs LINQ to SQL

LINQ to SQL only supports 1 to 1 mapping of database tables, views, sprocs and functions available in Microsoft SQL Server. It's a great API to use for quick data access construction to relatively well designed SQL Server databases. LINQ2SQL was first released with C# 3.0 and .Net Framework 3.5.

LINQ to Entities (ADO.Net Entity Framework) is an ORM (Object Relational Mapper) API which allows for a broad definition of object domain models and their relationships to many different ADO.Net data providers. As such, you can mix and match a number of different database vendors, application servers or protocols to design an aggregated mash-up of objects which are constructed from a variety of tables, sources, services, etc. ADO.Net Framework was released with the .Net Framework 3.5 SP1.

This is a good introductory article on MSDN: Introducing LINQ to Relational Data

C# – Linq2Sql: Manage DataContext

They really mean it with 'This is not supported.'. Attaching to an object fetched from another data context is not implemented.

There are a number of workarounds to the problem, the recommended way is by serializing objects, however this is not easy nor a clean approach.

The most simple approach I found is to use a readonly DataContext for fetching objects like this:

        MyDataContext dataContext = new MyDataContext() 
        { 
            DeferredLoadingEnabled = false, 
            ObjectTrackingEnabled = false 
        };

The objects obtained from this context can be attached to another context but only applies to some scenarios.

Best Answer

Related Solutions

.net – Entity Framework vs LINQ to SQL

C# – Linq2Sql: Manage DataContext

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