Automatically perform required conversions when query filter is defined on interface or base type

[nphmuller]

Say I have the following interface that can be implemented on any entity that I want to support soft-deletion.

public interface ISoftDeletableEntity
{
    bool IsDeleted { get; set; }
}

It would be nice to be able to define a global query filter for any entity type that implements this interface like this:

protected override void OnModelCreating(ModelBuilder modelBuilder)
{
    modelBuilder.Entity<ISoftDeletableEntity>().HasQueryFilter(e => e.IsDeleted == false);
}

Currently this throws the following exception: System.ArgumentException: 'The entity type 'MyApp.ISoftDeletableEntity' provided for the argument 'clrType' must be a reference type.'

[ajcvickers]

@nphmuller This is something that can be done with bulk configuration on the mapped entity types:

protected override void OnModelCreating(ModelBuilder modelBuilder)
{
    foreach (var entityType in modelBuilder.Model.GetEntityTypes()
        .Where(e => typeof(ISoftDeletableEntity).IsAssignableFrom(e.ClrType)))
    {
        modelBuilder
            .Entity(entityType.ClrType)
            .HasQueryFilter(ConvertFilterExpression<ISoftDeletableEntity>(e => !e.IsDeleted, entityType.ClrType));
    }
}

private static LambdaExpression ConvertFilterExpression<TInterface>(
    Expression<Func<TInterface, bool>> filterExpression, 
    Type entityType)
{
    var newParam = Expression.Parameter(entityType);
    var newBody = ReplacingExpressionVisitor.Replace(filterExpression.Parameters.Single(), newParam, filterExpression.Body);

    return Expression.Lambda(newBody, newParam);
}

Making a better experience around this is covered by #9117 and #6787.

The code is more complicated in this case than in many others because it requires constructing a lambda expression where the parameter is validated to be the exact entity type--not the interface. I'm going to re-purpose this bug to automatically handle base types/interfaces in EF code. After this issue is fixed it should be possible to simplify the above to:

protected override void OnModelCreating(ModelBuilder modelBuilder)
{
    Expression<Func<ISoftDeletableEntity, bool>> expression = e => !e.IsDeleted;

    foreach (var entityType in modelBuilder.Model.GetEntityTypes()
        .Where(e => typeof(ISoftDeletableEntity).IsAssignableFrom(e.ClrType)))
    {
        modelBuilder.Entity(entityType.ClrType).HasQueryFilter(expression);
    }
}

[HappyNomad]

@ajcvickers Wouldn't be more efficient to set IMutableEntityType.QueryFilter like my example at #8881 (comment)? That way you don't look up every affected entity type twice. Please "Automatically perform required conversions when query filter is defined" in that manner, too.

[nphmuller]

@ajcvickers
Nice. Was hoping it was possible already, but got stuck rewriting the expression. Thanks for the sample. It helps out a lot!

Totally agree with the repurpose. The sample after the fix is way easier to write.

[nphmuller]

I've set up a Gist which shows my query filter use-case and the code I had to write to get it working.
https://gist.github.com/nphmuller/8891c315d79aaaf720f9164cd0f10400
https://gist.github.com/nphmuller/05ff66dfa67e1d02cdefcd785661a34d

[ajcvickers]

Note from triage: if we implement this, then it will be as part of general mapping configuration for all uses of an interface, tracked by #6787.