LINQ to SQL - Compile error when extending data context with partial class and methods

Question

I am trying to use the Extensibility Method Definitions from my datacontext.designer.cs file to do some validation.

So I created a new file and added this code:

public partial class LawEnforcementDataContext : System.Data.Linq.DataContext
{

    partial void InsertCourse(Course instance) // this definition copied from generated file
    {
        ValidateCourse(instance);
        this.ExecuteDynamicInsert(instance);
    }

    partial void UpdateCourse(Course instance) // this definition copied from generated file
    {
        ValidateCourse(instance);
        this.ExecuteDynamicUpdate(instance);
    }

    private void ValidateCourse(Course instance)
    {
        if (instance.StartDate > instance.EndDate)
        {
            throw new ApplicationException("Start date cannot be later than end date.");
        }
    }
}

I can't compile because of these errors:

Error   1   No defining declaration found for implementing declaration of partial method 'LawEnforcementDataContext.InsertCourse(reservation.lawenforcement.Course)'
Error   2   No defining declaration found for implementing declaration of partial method 'LawEnforcementDataContext.UpdateCourse(reservation.lawenforcement.Course)'

I don't see what I am doing wrong. I have done this before. Also, after adding the above code, in code that references the classes created by the LINQ to SQL, it complains that my entity types no longer exist. It's as if the partial class LawEnforcementDataContext is completely taking over the generated code.

EDIT

Here are the other halves of the partial declarations from the generated code:

    // the class
    public partial class LawEnforcementDataContext : System.Data.Linq.DataContext

    // the methods
    partial void InsertCourse(Course instance);
    partial void UpdateCourse(Course instance);

Answer 1

Your two partial classes are defined in different namespaces, so the compiler does not 'share' them.

There is a setting under Properties in the DBML designer for this. Perhaps it reset?

Answer 2

In order to validate fields in Linq, you need to implement the OnValidate method not the Insert & Update methods.

For example:

partial void OnValidate(System.Data.Linq.ChangeAction action)
    {
        //All content items need titles
        if (Description == null || Description == "")
            throw new Exception("The description field is empty!");

        //Content types of image need...images
        if (ContentItemTypeId == (int)ContentItemTypes.Image && ImageData == null)
            throw new Exception("An image is required in order to save this content item!");

        //New Content Items don't have ids.  If a new one comes through, set the default values for it.
        if (this.ContentItemId == 0)
        {
            this.CreatedOn = DateTime.Now;
            this.LastUpdatedOn = DateTime.Now;
            this.IsDeletable = true;
        }
    }

Answer 3

Remove the partial keyword from your methods - the generated class does not have any partial methods.

Edit: Partial methods only work when they are defined like this:

partial class Foo
{
    partial void foo();
}

partial class Foo
{
    partial void foo() { }
}

One of the declarations needs to be written like it is an abstract method or interface method declaration. If the compiler finds one partial method with an implementation and cannot find the matching partial method declaration elsewhere it generates this error.

Edit: Here is something to check - is it possible that the parameter Course is not the exact same type in one of the two declarations? In other words is it possible that something like this has happened:

partial class Foo
{
    partial void foo(Biz.Parameter p);
}

partial class Foo
{
    partial void foo(Baz.Parameter p) { }
}

namespace Baz
{
    class Parameter { }
}

namespace Biz
{
    class Parameter { }
}

Answer 4

That error means that the partial method your are implementing has not been defined in the LawEnforcementDataContext class.

These methods should be automatically defined when you add tables into your DataContext, look in the generated source (probably LawEnforcement.designer.cs) for a region inside the LawEnforcementDataContext class labelled #region Extensibility Method Definitions all the partial methods will be defined here. I expect the methods will be missing, try removing and re-adding the Course table in your Linq model to generate them.

Answer 5

To clarify, it's the class that's partial, not the methods within it - the DataContext class generated by L2S is a partial class but doesn't contain any partial methods ** correction below **.

For clarification on the difference of defining and implementing partial method declarations, this might help.

Edit

Well I never - I'd not seen/used "#region Extensibility Method Definitions" methods before... you learn something every day! Anyway, the article I linked to is a useful discussion on partial methods in general, separate from L2S.

Answer 6

Ronnie, I just ran into this same issue. Caveat: Be cautious when you have multiple classes in one entity file.

Check where the partial class located: Did you accidentally put the definition inside the data context brackets like I did?