Cannot pass a field with an interface type into an EF extension

[makingbloke]

Bug description

I have created a DBFunctions / IMethodCallTranslator extension called FreeTextSearch (The idea being that it provides a wrapper round the SQLite free text search Match method).

The prototype for the extension is in DbFunctionsExtensions.cs:

public static bool FreeTextSearch(this DbFunctions _, object propertyReference, string freeText, [NotParameterized]IFreeTextConfig config) => throw new NotImplementedException("This method is for use with Entity Framework Core only and has no in-memory implementation.");

When the extension is called like this (in Tests.cs):

IFreeTextConfig config = new SqliteFreeTextConfig(); IQueryable<TestTableDto> query = context.TestTable.Where(e => EF.Functions.FreeTextSearch(e.TextContent!, "MIKE", config));

The translator fails to get called and the an InvalidOperationException with the text shown below is raised:

System.InvalidOperationException: 'The LINQ expression 'DbSet()
.Where(t => __Functions_0
.FreeTextSearch(
propertyReference: t.TextContent,
freeText: "MIKE",
config: (IFreeTextConfig)SqliteFreeTextConfig))' could not be translated. Either rewrite the query in a form that can be translated, or switch to client evaluation explicitly by inserting a call to 'AsEnumerable', 'AsAsyncEnumerable', 'ToList', or 'ToListAsync'. See https://go.microsoft.com/fwlink/?linkid=2101038 for more information.'

However, when I change IFreeTextConfig to SqliteFreeTextConfig (see below) then it works fine and the translator code gets called.

SqliteFreeTextConfig config = new SqliteFreeTextConfig(); IQueryable<TestTableDto> query = context.TestTable.Where(e => EF.Functions.FreeTextSearch(e.TextContent!, "MIKE", config));

The argument config in the method FreeTextSearch is type IFreeTextConfig so why does it not work if I pass an interface but does when I pass a concrete class?

Attached is a project that can be used to demonstrate the issue.

Thanks,

Mike

EntityFrameworkTest.zip

Your code

.

Stack traces

Verbose output

EF Core version

9.0.2

Database provider

Microsoft.EntityFrameworkCore.Sqlite

Target framework

.Net 9.0

Operating system

Windows 11

IDE

Visual Studio 2022 17.13.2

[roji]

This is likely because in the expression tree, a Convert node is introduced to cast up from SqliteFreeTextConfig to IFreeTextConfig, and that blocks usage of the IMethodTranslator (since it's a complex fragment etc). We can look into handling more Convert node scenarios, but this is a quite niche and we're very unlikely to get around to any time soon - I'm placing this in the backlog.

In the meantime, avoid using interfaces here and just pass the concrete type.

[makingbloke]

Thanks, Now I know what the issue is I can code round it.