Unable to cast "System.Linq.Expressions.UnaryExpression" to "System.Linq.Expressions.LambdaExpression".

[emejibka]

Hello.
After update from 5.2.7 to 5.3.* we have some issue with custom QueryProvider. I make test application -
https://github.com/emejibka/nhibernate-specification-subquery-bug

System.NotSupportedException : Could not parse expression 'value(NHibernate.Linq.NhQueryable`1[TestApp.Client]).Where(Convert(value(TestApp.Specification`1[TestApp.Client])))': The given arguments did not match the expected arguments: Невозможно преобразовать объект типа "System.Linq.Expressions.UnaryExpression" к типу "System.Linq.Expressions.LambdaExpression".
   в Remotion.Linq.Parsing.Structure.MethodCallExpressionParser.CreateExpressionNode(Type nodeType, MethodCallExpressionParseInfo parseInfo, Object[] additionalConstructorParameters)
   в Remotion.Linq.Parsing.Structure.MethodCallExpressionParser.Parse(String associatedIdentifier, IExpressionNode source, IEnumerable`1 arguments, MethodCallExpression expressionToParse)
   в Remotion.Linq.Parsing.Structure.ExpressionTreeParser.ParseMethodCallExpression(MethodCallExpression methodCallExpression, String associatedIdentifier)
   в Remotion.Linq.Parsing.Structure.ExpressionTreeParser.ParseMethodCallExpression(MethodCallExpression methodCallExpression, String associatedIdentifier)
   в Remotion.Linq.Parsing.Structure.ExpressionTreeParser.ParseTree(Expression expressionTree)
   в Remotion.Linq.Parsing.Structure.QueryParser.GetParsedQuery(Expression expressionTreeRoot)
   в Remotion.Linq.Parsing.ExpressionVisitors.SubQueryFindingExpressionVisitor.Visit(Expression expression)
   в System.Linq.Expressions.ExpressionVisitor.VisitLambda[T](Expression`1 node)
   в Remotion.Linq.Parsing.ExpressionVisitors.SubQueryFindingExpressionVisitor.Visit(Expression expression)
   в Remotion.Linq.Parsing.Structure.MethodCallExpressionParser.ProcessArgumentExpression(Expression argumentExpression)
   в System.Linq.Enumerable.WhereSelectEnumerableIterator`2.MoveNext()
   в System.Linq.Buffer`1..ctor(IEnumerable`1 source)
   в System.Linq.Enumerable.ToArray[TSource](IEnumerable`1 source)
   в Remotion.Linq.Parsing.Structure.MethodCallExpressionParser.Parse(String associatedIdentifier, IExpressionNode source, IEnumerable`1 arguments, MethodCallExpression expressionToParse)
   в Remotion.Linq.Parsing.Structure.ExpressionTreeParser.ParseMethodCallExpression(MethodCallExpression methodCallExpression, String associatedIdentifier)
   в Remotion.Linq.Parsing.Structure.ExpressionTreeParser.ParseTree(Expression expressionTree)
   в Remotion.Linq.Parsing.Structure.QueryParser.GetParsedQuery(Expression expressionTreeRoot)
   в NHibernate.Linq.NhLinqExpression.Translate(ISessionFactoryImplementor sessionFactory, Boolean filter)
   в NHibernate.Hql.Ast.ANTLR.ASTQueryTranslatorFactory.CreateQueryTranslators(IQueryExpression queryExpression, String collectionRole, Boolean shallow, IDictionary`2 filters, ISessionFactoryImplementor factory)
   в NHibernate.Engine.Query.QueryPlanCache.GetHQLQueryPlan(IQueryExpression queryExpression, Boolean shallow, IDictionary`2 enabledFilters)
   в NHibernate.Impl.AbstractSessionImpl.GetHQLQueryPlan(IQueryExpression queryExpression, Boolean shallow)
   в NHibernate.Impl.AbstractSessionImpl.CreateQuery(IQueryExpression queryExpression)
   в NHibernate.Linq.DefaultQueryProvider.PrepareQuery(Expression expression, IQuery& query)
   в TestApp.CustomQueryProvider.PrepareQuery(Expression expression, IQuery& query) в C:\temp\nhibernate-specification-subquery-bug\CustomQueryProvider.cs:строка 17
   в NHibernate.Linq.DefaultQueryProvider.ExecuteList[TResult](Expression expression)
   в NHibernate.Linq.NhQueryable`1.System.Collections.Generic.IEnumerable<T>.GetEnumerator()
   в System.Collections.Generic.List`1..ctor(IEnumerable`1 collection)
   в System.Linq.Enumerable.ToList[TSource](IEnumerable`1 source)
   в TestApp.TestClass.test() в C:\temp\nhibernate-specification-subquery-bug\TestClass.cs:строка 48

[bahusoid]

Yes it's reproducible on 5.3.3 and has nothing to do with custom provider. It's something related to implicit conversion to expression.
Can be reproduced by adding the following code to LinqQuerySamples:

public class Specification<T>
{
	private Expression<Func<T, bool>> _expression;

	public Specification(Expression<Func<T, bool>> expression)
	{
		_expression = expression;
	}

	public static implicit operator Expression<Func<T, bool>>(Specification<T> specification)
	{
		return specification._expression;
	}
}

[Test]
public void ImplicitConversionInsideWhereSubqueryExpression()
{
	var spec = new Specification<Order>(x => x.Freight > 1000);

	db.Orders.Where(o => db.Orders.Where(spec).Any(x => x.OrderId == o.OrderId)).ToList();
}

[bahusoid]

As a workaround you can try to add the following code to SpecificationsProcessor skipping implicit conversion from parsing:

protected override Expression VisitUnary(UnaryExpression node)
{
    if (node.NodeType == ExpressionType.Convert && typeof(BaseSpecification).IsAssignableFrom(node.Operand.Type))
    {
        return ((BaseSpecification)FindValue(node.Operand)).ToExpression();
    }
    return base.VisitUnary(node);
}

private static object FindValue(Expression expression)
{
    if (expression.NodeType == ExpressionType.MemberAccess)
    {
        var memberAccess = (MemberExpression) expression;
        if (memberAccess.Expression == null || memberAccess.Expression.NodeType == ExpressionType.Constant)
        {
            var constantValue = ((ConstantExpression) memberAccess.Expression)?.Value;
            var member = memberAccess.Member;
            switch (member.MemberType)
            {
                case MemberTypes.Field:
                    return ((FieldInfo) member).GetValue(constantValue);
                case MemberTypes.Property:
                    return ((PropertyInfo) member).GetValue(constantValue);
            }
        }
    }
    
    throw new NotSupportedException();
}

Also in 5.3 you can drop all IQueryProviderWithOptions related code from CustomQueryProvider and instead override CreateWithOptions:

protected override IQueryProvider CreateWithOptions(NhQueryableOptions options)
{
    return new CustomQueryProvider(Session, Collection, options);
}
private CustomQueryProvider(ISessionImplementor session, object collection, NhQueryableOptions options): base(session, collection, options)
{
}

[hazzik]

What is the type of unary expression? Is it Quote?

[bahusoid]

I suspect it's Convert