Attempting to use EF Core with LinqPad getting unable to case to DbContext

Omnius

I am using EF Core 2.0.3 in an application. I can create a connection to the database using the DbContext DLL and the constructor that takes a connection string. The test button says everything is working. However, in the connection list I am getting the error: "Unable to cast object of type "...GorillaSyncDbContext" to type "Microsoft.EntityFrameworkCore.DbContext".

That type is definitely inherited from Microsoft.EntityFrameworkCore.DbContext. I have added the Nuget Package for Microsoft.EntityFrameworkCore v2.0.3 and Microsoft.EntityFrameworkCore.SqlServer v2.0.3 to LinqPad (or maybe just to the query). This caused no change.

What am I missing?

Thanks in advance for any advice.

Omnius

More information. Even though I am getting that error in the left connection list, if I do from x in TableName select x I get the same error about not being able to cast do DbContext.

However, if I do TableName.Dump() I do get results back. Most, but not all, of the fluent methods appear to work against the database. Strangely for some tables I get the cast error and not others. I haven't seen a clear pattern.

Omnius

Even more information. It turns out that the cast errors aren't persistent. If I get a cast error and then I query another table (that works) and come back to the call that returned a cast error it often works just fine. So, it's relatively random. Even the error on linq (versus fluent) queries has turned out to be temporary. Weird.

JoeAlbahari

One possible cause is multiple conflicting copies of the Entity Framework assemblies. You can check for this by inserting the following query before the query which fails:

AppDomain.CurrentDomain.GetAssemblies()
	.OrderBy (a => a.GetName().Name)
	.Select (a => new { a.GetName().Name, a.Location })
	.Dump();

Omnius

I couldn't run that query directly because I got the error, "The invoked member is not supported in a dynamic assembly." by which it means GetName(). But, by changing the query to this:

var q1 = AppDomain.CurrentDomain.GetAssemblies();

var assemblyList = new List();
foreach (var x in q1)
{
    try
    {
        assemblyList.Add($"{x.GetName().Name} ({x.Location})");
    }
    catch (Exception e)
    {
        assemblyList.Add(e.Message);
    }
}

assemblyList.OrderBy(a => a).Dump();

I was able to get the following list. I don't know if it's part of the problem, but the assembly that shall not be named only provides this in the debugger:
Anonymously Hosted DynamicMethods Assembly, Version=0.0.0.0, Culture=neutral, PublicKeyToken=null

The list was too long to paste here, so I put it in this Google Doc: https://docs.google.com/document/d/1vEmWhuRQm020p5OLwrH4olUX3QdXmh4BlWEpdzVOBqE/edit?usp=sharing

For reference, I have also listed the DLLs that I see in a new, unattached, LinqPad document. There is no anonymous assembly and your original code works fine there.

Omnius

I updated the list again. I had been playing with different things trying to resolve the problem and one of the things that was suggested in a forum was copying the EF DLLs to the LinqPad EXE location. I had done that before I ran the first list, but it hadn't had any effect. LinqPad was loading those DLLs though, so I cleared them out of the program files, ran LinqPad again. and pulled a new list of DLLs. Also, just so you can see it, here is a screenshot showing the error in the connection list:



Not sure why the image isn't showing up, here's the bare link:
https://drive.google.com/file/d/1lZM9NRwLRJRmDQapFudXRuHzYBlZejXh/view?usp=sharing