MappedAs throws when called on a Convert UnaryExpression

[alexrootes]

In an apparent regression between 5.2.7 and 5.3.0 this code will throw where it did not before:

q = q.Where(r => r.Labels == ((IntArray)labels).MappedAs(CustomType.IntArrayType));

HibernateException: MappedAs must be called on an expression which can be evaluated as ConstantExpression. It was call on UnaryExpression instead.

As a workaround removing the inline cast resolves the issue:

var convertedLabels = (IntArray)labels;
q = q.Where(r => r.Labels == convertedLabels.MappedAs(CustomType.IntArrayType));

This could possibly be a result of changes in #2365

[fredericDelaporte]

Have you checked if the trouble does still occur with 5.3.7?

[alexrootes]

Yes same issue under 5.3.7.

[bahusoid]

Issue aside. Is MappedAs still required for this case in 5.3? I believe #2365 should make it work without explicit MappedAs call:

q.Where(r => r.Labels == ((IntArray)labels))

[alexrootes]

Thanks @bahusoid I can confirm that code does indeed work. I did simplify the original code to better illustrate the issue however, the full version looks like this:

q.Where(r => r.Labels.Contains(((IntArray)labels).MappedAs(CustomType.IntArrayType)));

Where Contains is a custom Linq method hooked to an HQL function generator. Omitting the MappedAs call from that throws:

HibernateException: Could not determine a type for class: IntArray

I would like to understand how to resolve that but it's probably outside the scope of this issue.

I can workaround by directly constructing an IntArray instance rather than converting:

q.Where(r => r.Labels.Contains(new IntArray(labels).MappedAs(CustomType.IntArrayType)));

[bahusoid]

Hm... Not sure how it supposed to work for custom generators. Also your original code does not look right - Contains expect collection element as a parameter - from your example it seems you supply collections on both sides of Contains.

From quick glance at code it seems auto detection is currently implemented only for inversed case:

q.Where( r = > new IntArray(labels).Contains(r.Label)); //Contains is called on parameter, not on mapped property

So MappedAs might be still required in your case.

[alexrootes]

Yes this is why Contains is a custom Linq method, it boils down to a pg array contains operator @> https://www.postgresql.org/docs/current/functions-array.html#ARRAY-OPERATORS-TABLE

[bahusoid]

I would like to understand how to resolve that but it's probably outside the scope of this issue

You can map globally custom type using TypeFactory.RegisterType. Something like:

//Before building NHibernate configuration
TypeFactory.RegisterType(typeof(IntArray), CustomType.IntArrayType, TypeFactory.EmptyAliases);

[fredericDelaporte]

Fixed by #2711