C# – Linq to SQL Insert Error

clinq-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.

This is the error message I am getting when I try to run the following, roughly:

1 DataContext db = new DataContext();
2 o = new object();
3 o.association = db.GetAssociatedObject(pId);
4 db.objects.InsertOnSubmit(o);
5 db.SubmitChanges();

This code creates a new object, populates an association with an existing object, then inserts the new object. When I comment out line 3+4, the error goes away. What causes the error? Can I not do an insert with associated objects?

Best Answer

This is probably because you are maintaining a bidirectional relationship between o and its associated object. When you tell the DataContext to Insert o, its associated object is duplicated in the DataContext's object tracking graph (one time as loaded and another time as Insert for o).

Commenting out line 4 should resolve the issue, but leave you with a correct association between o and o.association.

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.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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