EF Core Fluent API to get inheritance properties

Question

How to use EF Core Fluent API to get inheritance properties?

I have a base class and 2 inherited children classes:

class BaseClass
{
    public string Name { get; set; }
}

class Child1 : BaseClass
{
   public string Foo { get; set; }
}

class Child2 : BaseClass
{
   public string Bar { get; set; }
}

class DBContext
{
   ...
   public List<BaseClass> BaseClasses { get; set; }
   ...

   protected override void OnModelCreating(ModelBuilder modelBuilder)
   {
      modelBuilder.Entity<BaseClass>(entity =>
      {
        entity.HasDiscriminator<string>("Discriminator")
                    .HasValue<Child1>(nameof(Child1))
                    .HasValue<Child2>(nameof(Child2))
                    .IsComplete(false);

        entity.Property("Discriminator")
                .IsUnicode(false)
                .HasMaxLength(60);

      });
   }
}

But the following query:

_dBContext.BaseClasses
          .Where(x => x is Child2 && EF.Property<string>(x, "Bar") == "ABC")
          .ToList();

Throws the following error:

Translation of 'EF.Property(StructuralTypeShaperExpression: BaseClasses
ValueBufferExpression: ProjectionBindingExpression: EmptyProjectionMember
IsNullable: False , "Bar")' failed. Either the query source is not an entity type, or the specified property does not exist on the entity type.

It looks the issue is in IsNullable, but I have no idea how to fix it.

Thanks

Does using Queryable.OfType<TResult> help you here? E.g. _dbContext.BaseClasses.OfType<Child2>().Where(x => x.Bar == "ABC")) — nbokmans
– nbokmans, Commented Jun 25 at 16:14
How about .Where(x => x is Child2 && ((Child2)x).Bar == "ABC")? Because c# cast is the typical way of accessing derived members in EFC. Or EF.Property<string>((Child2)x, "Bar"). Looks like EFC is trying to bind property Bar to BaseClass which of course doesn't exist. — Ivan Stoev
– Ivan Stoev, Commented Jun 25 at 19:12
You can also expose DbSets of the inherited types, for instance DbSet<Child1> Child1s { get; protected set; } etc. — Steve Py
– Steve Py, Commented Jun 25 at 20:42

Marc LaFleur · Accepted Answer · 2025-06-25 17:57:42Z

1

To get around this, you'll want break apply two distinct filters. The first will get a collection of Child2 types. The second will filter that collection on the Bar value.

_dBContext.BaseClasses // returns a `IQueryable<BaseClass>`
  .OfType<Child2>() // returns a `IQueryable<Child2>`
  .Where(x => x.Bar == "ABC";

Breaking the lambda into its consituent parts would look like this:

IQueryable<BaseClass> baseCollection = _dBContext.BaseClasses;
IQueryable<Child2> child2Collection = baseCollection.OfType<Child2>();
IEnumerable filteredCollection = child2Collection.Where(x => x.Bar == "ABC";

EDIT: Posted before I noticed the comment from nbokmans. He deserves the credit.

answered Jun 25 at 17:57

Marc LaFleur

33.4k4 gold badges41 silver badges71 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

Michał Turczyn · Accepted Answer · 2025-06-29 13:20:35Z

For me this Where filter worked perfectly:

var children = await dbContext.BaseClasses
    .Where(x => x is Child2 && (x as Child2).Bar == "ABC")
    .ToArrayAsync();

You could even define conveniency method WhereChild to simplify this:

public static class Extensions
{
    public static IQueryable<TSource> WhereChild<TSource, TChild>(
        this IQueryable<TSource> source, 
        Expression<Func<TChild, bool>> predicate)
        where TChild : class, TSource
    {
        var parameter = Expression.Parameter(typeof(TSource), "x");

        var isType = Expression.TypeIs(parameter, typeof(TChild)); // x is TChild

        var cast = Expression.TypeAs(parameter, typeof(TChild));   // (TChild)x

        var invokedPredicate = Expression.Invoke(predicate, cast); // predicate((TChild)x)

        var andExpression = Expression.AndAlso(isType, invokedPredicate);

        var lambda = Expression.Lambda<Func<TSource, bool>>(andExpression, parameter);

        return source.Where(lambda);
    }
}

and the usage would be

var children = await dbContext.BaseClasses
    .WhereChild((Child2 c) => c.Bar == "ABC")
    .ToArrayAsync();

Collectives™ on Stack Overflow

EF Core Fluent API to get inheritance properties

2 Answers 2

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related