QueryableExtensions: NullableExpressionBinder used in preference to CustomExpressionBinder

[roblugt]

The following example demonstrates a problem where the NullableExpressionBinder is selected even though a custom ProjectUsing expression is configured. This results in an InvalidOperationException

No coercion operator is defined between types 'System.String' and 'System.Nullable`1[AutomapperEnumTest.Method]'.

using System;
using System.Linq;
using AutoMapper;
using AutoMapper.QueryableExtensions;

namespace AutomapperEnumTest
{
	public enum Method
	{
		MANUAL = 0,
		AUTO = 1
	}

	public class DestType
	{
		public string Name { get; set; }
		public Method? Method { get; set; }
	}

	public class SourceType
	{
		public string Name { get; set; }
		public string MethodName { get; set; }
	}

	public class Program
	{
		public static void Main()
		{
			Configure();
			var src = new SourceType[] { new SourceType { Name = "Rob", MethodName = "AUTO" } };
			var results = src.AsQueryable()
						.ProjectTo<DestType>();
		}

		private static void Configure()
		{
			Mapper.Initialize(cfg =>
			{
				cfg.CreateMap<string, Method?>().ProjectUsing(src => src == "MANUAL" ? Method.MANUAL : Method.AUTO);
				cfg.CreateMap<SourceType, DestType>()
					.ForMember(dest => dest.Method, opt => opt.MapFrom(src => src.MethodName));
			});
		}
	}
}

Perhaps the ExpressionBuilder class should change the order of Builders so that CustomProjectionExpressionBinder is listed first?

[lbargaoanu]

Sounds reasonable. PR?

[roblugt]

Thanks PR #1890 created.

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