Inner query OfType EFcore

Question

I have a model that looks like this:

Product
 -DeleteProduct
  └─PreviousProduct (of type SubProduct, not DeleteProduct)
      
 -SubProduct of type SubProduct1, SubProduct2

So in words, the product can be of type DeleteProduct or of type SubProduct, if it's of DeleteProduct then it has a property PreviousProduct (of type SubProduct)

Now I have a the following EF Core linq query like so:

var queryable = context
                .Set<Product>()
                .OfTypes(new[] { typeof(SubProduct1), typeof(DeleteProduct) })
                .Where(p => p.CustomerId == customerId && op.CustomerId != null)
                .Where(p => op is SubProduct1 || (op is DeleteProduct && op.PreviousProduct is AccessProduct))
                .Select(p => p.ProductId);

With some extension methods, (with thanks to Drew):

public static IQueryable<TEntity> NotOfTypes<TEntity>(this IQueryable<TEntity> query, IEnumerable<Type>? typesEnumerable) where TEntity : class
{
    return AddWhere(query, typesEnumerable, types => GetNotTypesPredicate(typeof(TEntity), types));
}

public static IQueryable<TEntity> OfTypes<TEntity>(this IQueryable<TEntity> query, IEnumerable<Type>? typesEnumerable) where TEntity : class
{
    return AddWhere(query, typesEnumerable, types => GetOfOnlyTypesPredicate(typeof(TEntity), types));
}

private static IQueryable<TEntity> AddWhere<TEntity>(
    this IQueryable<TEntity> query,
    IEnumerable<Type>? typesEnumerable,
    Func<IReadOnlyList<Type>, LambdaExpression> getNotTypesPredicate) where TEntity : class
{
    if (typesEnumerable is null)
    {
        return query;
    }

    var types = typesEnumerable.ToArray();

    if (!types.Any())
    {
        return query;
    }

    var lambda = getNotTypesPredicate(types);

    return query.OfType<TEntity>().Where(lambda as Expression<Func<TEntity, bool>> ??
                                         throw new InvalidOperationException("Could not translate to types"));
}

private static LambdaExpression GetNotTypesPredicate(Type baseType, IReadOnlyList<Type> excluded)
{ 
    var param = Expression.Parameter(baseType, "notOfTypeParam");
    Expression merged = Expression.Not(Expression.TypeIs(param, excluded[0]));

    for (var i = 1; i < excluded.Count; i++)
    {
        merged = Expression.AndAlso(merged, Expression.Not(Expression.TypeIs(param, excluded[i])));
    }

    return Expression.Lambda(merged, param);
}

private static LambdaExpression GetOfOnlyTypesPredicate(Type baseType, IReadOnlyList<Type> allowed)
{
    var param = Expression.Parameter(baseType, "typeonlyParam");
    Expression merged = Expression.TypeIs(param, allowed[0]);

    for (var i = 1; i < allowed.Count; i++)
    {
        merged = Expression.OrElse(merged, Expression.TypeIs(param, allowed[i]));
    }

    return Expression.Lambda(merged, param);
}

EntityFrameworkCore comes up with the following query (I simplified the query a bit by removing the unneeded parentheses and casts):

DECLARE @__customerId_0 int = 1;

SELECT [p].[ProductId]
FROM [dbo].[Product] AS [p]
LEFT JOIN (
 SELECT [p0].[ProductId], [p0].[ProductTypeId]
 FROM [dbo].[Product] AS [p0]
 WHERE [p0].[ProductTypeId] IN (1, 2, 3, 9, 10, 20, 21, 22, 30, 31)
 ) AS [t] ON [p].[PreviousProductId] = [t].[ProductId]
WHERE 
(
 [p].[ProductTypeId] IN (1, 0)
 AND [p].[CustomerId] = @__customerId_0
 )
 AND 
 (
     [p].[ProductTypeId] = 1
     OR ([p].[ProductTypeId] = 0 AND [t].[ProductTypeId] = 1)
 )

As you can see the OfTypes already and does the [ProductTypeId] IN (1, 0)

I would like to get rid of the unneeded [ProductTypeId] IN (1, 2, 3, 9, 10, 20, 21, 22, 30, 31) and have that changed into ProductTypeId = 1 or ProductTypeId in (1)

How do I do this? Maybe LinqKit can do this? With a nested expression or so?

Answer 1

It is possible, if you add DbContext as additional paramateter. DbContext needed to get Model information.

Usage almost the same:

var queryable = context
    .Set<Product>()
    .OfTypes(context, new[] { typeof(SubProduct1), typeof(DeleteProduct) })
    .Where(p => p.CustomerId == customerId && op.CustomerId != null)
    .Where(p => op is SubProduct1 || (op is DeleteProduct && op.PreviousProduct is AccessProduct))
    .Select(p => p.ProductId);

And implementation:

public static class TPHExtemsions
{
    public static IQueryable<TEntity> OfTypes<TEntity>(this IQueryable<TEntity> query, DbContext context,
        IEnumerable<Type>? typesEnumerable)
    {
        var predicate = BuildPredicate<TEntity>(context.Model, typesEnumerable, false);
        if (predicate == null)
            return query;

        return query.Where(predicate);
    }

    public static IQueryable<TEntity> NotOfTypes<TEntity>(this IQueryable<TEntity> query, DbContext context,
        IEnumerable<Type>? typesEnumerable)
    {
        var predicate = BuildPredicate<TEntity>(context.Model, typesEnumerable, true);
        if (predicate == null)
            return query;

        return query.Where(predicate);
    }

    private static Expression<Func<TEntity, bool>> BuildPredicate<TEntity>(IModel model,
        IEnumerable<Type>? typesEnumerable, bool isNot)
    {
        if (typesEnumerable == null)
            return null;

        // get Discriminator values from model
        var discriminatorValues = typesEnumerable.Select(t => model.FindEntityType(t).GetDiscriminatorValue()).ToList();
        if (discriminatorValues.Count == 0)
            return null;

        var et = model.FindEntityType(typeof(TEntity));

        var discriminator = et.GetDiscriminatorProperty();

        // cast List of objects to discriminator type
        var itemsExpression = Expression.Call(typeof(Enumerable), nameof(Enumerable.Cast),
            new[] { discriminator.ClrType }, Expression.Constant(discriminatorValues));

        var param = Expression.Parameter(typeof(TEntity), "e");

        Expression propExpression;
        if (discriminator.PropertyInfo == null)
        {
            // Discriminator is Shadow property, so call via EF.Property(e, "Discriminator")
            propExpression = Expression.Call(typeof(EF), nameof(EF.Property), new[] { discriminator.ClrType },
                param, Expression.Constant(discriminator.Name));
        }
        else
        {
            propExpression = Expression.MakeMemberAccess(param, discriminator.PropertyInfo);
        }

        // generate Contains
        var predicate = (Expression)Expression.Call(typeof(Enumerable), nameof(Enumerable.Contains), new[] { discriminator.ClrType },
            itemsExpression, propExpression);

        // invert if needed
        if (isNot)
            predicate = Expression.Not(predicate);

        // generate lambda from predicate
        var predicateLambda = Expression.Lambda<Func<TEntity, bool>>(predicate, param);

        return predicateLambda;
    }
}