Filtering is not working on Nullable properties

[j2lab]

Steps to reproduce.

1. Create a model that has a nullable property.
2. Use the nullable property for filtering collection

Actual Result

System.InvalidOperationException : The binary operator Equal is not defined for the types 'System.Nullable`1[System.Int32]' and 'System.Int32'.

Stack Trace: 
Expression.GetEqualityComparisonOperator(ExpressionType binaryType, String opName, Expression left, Expression right, Boolean liftToNull)
Expression.Equal(Expression left, Expression right, Boolean liftToNull, MethodInfo method)
Expression.Equal(Expression left, Expression right)
DynamicExpressions.RobustEquals(MemberExpression prop, ConstantExpression constant) line 89
DynamicExpressions.CreateFilter(MemberExpression prop, FilterOperator op, ConstantExpression constant) line 62
DynamicExpressions.GetFilter(ParameterExpression param, String property, FilterOperator op, Object value) line 55
DynamicExpressions.GetPredicate[TEntity](String property, FilterOperator op, Object value) line 37
PredicateTests.GetPredicate_ShouldHandleNumericalOperators(Int32 id, String title, String property, FilterOperator op, Object value) line 22

[j2lab]

Here is a fix for the nullable filter. Please review it

 private static Expression CreateFilter(MemberExpression prop, FilterOperator op, ConstantExpression constant)
        {
            if (prop.Type.Name.StartsWith("Nullable"))
            {
                var hasValueExpression = Expression.Property(prop, "HasValue");
                var valueExpression = Expression.Property(prop, "Value");

                var comparisonExpression = GenerateExpression(valueExpression, op, constant);

                return Expression.AndAlso(hasValueExpression, comparisonExpression);
            }
            else
                return GenerateExpression(prop, op, constant);
        }

        private static Expression GenerateExpression(MemberExpression prop, FilterOperator op, ConstantExpression constant)
        {
            return op switch
            {
                FilterOperator.Equals => RobustEquals(prop, constant),
                FilterOperator.GreaterThan => Expression.GreaterThan(prop, constant),
                FilterOperator.LessThan => Expression.LessThan(prop, constant),
                FilterOperator.ContainsIgnoreCase => Expression.Call(prop, _stringContainsMethodIgnoreCase, PrepareConstant(constant), Expression.Constant(StringComparison.OrdinalIgnoreCase)),
                FilterOperator.Contains => GetContainsMethodCallExpression(prop, constant),
                FilterOperator.NotContains => Expression.Not(GetContainsMethodCallExpression(prop, constant)),
                FilterOperator.ContainsKey => Expression.Call(prop, _dictionaryContainsKeyMethod, PrepareConstant(constant)),
                FilterOperator.NotContainsKey => Expression.Not(Expression.Call(prop, _dictionaryContainsKeyMethod, PrepareConstant(constant))),
                FilterOperator.ContainsValue => Expression.Call(prop, _dictionaryContainsValueMethod, PrepareConstant(constant)),
                FilterOperator.NotContainsValue => Expression.Not(Expression.Call(prop, _dictionaryContainsValueMethod, PrepareConstant(constant))),
                FilterOperator.StartsWith => Expression.Call(prop, _startsWithMethod, PrepareConstant(constant)),
                FilterOperator.EndsWith => Expression.Call(prop, _endsWithMethod, PrepareConstant(constant)),
                FilterOperator.DoesntEqual => Expression.Not(RobustEquals(prop, constant)),
                FilterOperator.GreaterThanOrEqual => Expression.GreaterThanOrEqual(prop, constant),
                FilterOperator.LessThanOrEqual => Expression.LessThanOrEqual(prop, constant),
                FilterOperator.IsEmpty => Expression.Call(_isNullOrEmtpyMethod, prop),
                FilterOperator.IsNotEmpty => Expression.Not(Expression.Call(_isNullOrEmtpyMethod, prop)),
                _ => throw new NotImplementedException()
            };
        }

[grgoncal]

Can someone review this?

[rene-mandel]

This needs attention.

[shawn-peery]

Just a mention here, it seems that this issue only occurs for Int32s. as when I try the same code with String's it doesn't have that issue.

Also looks like the issue happens on enum types as well

[zHaytam]

I don't know why I was not receiving notifications for this repo...
I will look into this issue as soon as I can, sorry!