NH-3094 - Support unary minus and plus operators in LINQ (#563)

Author: PleasantD

src/NHibernate.Test/Linq/OperatorTests.cs

@@ -1,6 +1,7 @@
 using System;
 using System.Collections.Generic;
 using System.Linq;
+using System.Linq.Expressions;
 using System.Text;
 using NHibernate.DomainModel.Northwind.Entities;
 using NHibernate.Linq;
@@ -16,5 +17,21 @@ public void Mod()
         {
             Assert.AreEqual(2, session.Query<TimesheetEntry>().Where(a => a.NumberOfHours % 7 == 0).Count());
         }
-    }
+
+		[Test]
+		public void UnaryMinus()
+		{
+			Assert.AreEqual(1, session.Query<TimesheetEntry>().Count(a => -a.NumberOfHours == -7));
+		}
+
+		[Test]
+		public void UnaryPlus()
+		{
+			// Ensure expression tree contains UnaryPlus
+			var param = Expression.Parameter(typeof(TimesheetEntry), "e");
+			var expr = Expression.Equal(Expression.UnaryPlus(Expression.PropertyOrField(param, "NumberOfHours")), Expression.Constant(7));
+			var predicate = Expression.Lambda<Func<TimesheetEntry, bool>>(expr, param);
+			Assert.AreEqual(1, session.Query<TimesheetEntry>().Count(predicate));
+		}
+	}
 }

src/NHibernate/Hql/Ast/HqlTreeBuilder.cs

@@ -124,6 +124,11 @@ public HqlDivide Divide(HqlExpression lhs, HqlExpression rhs)
 			return new HqlDivide(_factory, lhs, rhs);
 		}
 
+		public HqlNegate Negate(HqlExpression expression)
+		{
+			return new HqlNegate(_factory, expression);
+		}
+
 		public HqlDot Dot(HqlExpression lhs, HqlExpression rhs)
 		{
 			return new HqlDot(_factory, lhs, rhs);

src/NHibernate/Hql/Ast/HqlTreeNode.cs

@@ -322,6 +322,14 @@ public HqlAdd(IASTFactory factory, HqlExpression lhs, HqlExpression rhs)
 		}
 	}
 
+	public class HqlNegate : HqlExpression
+	{
+		public HqlNegate(IASTFactory factory, HqlExpression expression)
+			: base(HqlSqlWalker.UNARY_MINUS, "-", factory, expression)
+		{
+		}
+	}
+
 	public class HqlBooleanOr : HqlBooleanExpression
 	{
 		public HqlBooleanOr(IASTFactory factory, HqlBooleanExpression lhs, HqlBooleanExpression rhs)

src/NHibernate/Linq/Visitors/HqlGeneratorExpressionTreeVisitor.cs

@@ -438,6 +438,10 @@ protected HqlTreeNode VisitUnaryExpression(UnaryExpression expression)
 		{
 			switch (expression.NodeType)
 			{
+				case ExpressionType.Negate:
+					return _hqlTreeBuilder.Negate(VisitExpression(expression.Operand).AsExpression());
+				case ExpressionType.UnaryPlus:
+					return VisitExpression(expression.Operand).AsExpression();
 				case ExpressionType.Not:
 					return _hqlTreeBuilder.BooleanNot(VisitExpression(expression.Operand).ToBooleanExpression());
 				case ExpressionType.Convert: