Add support for Decimal.Truncate

In Firebird the function is called 'trunc'
MySQL requires the number of decimals to be specified

Author: weelink

src/NHibernate.Test/NHSpecificTest/GH0831/FixtureByCode.cs

@@ -203,6 +203,18 @@ public void CanHandleSubtract()
 			});
 		}
 
+		[Test]
+		public void CanHandleTruncate()
+		{
+			AssumeFunctionSupported("truncate");
+
+			Assert.Multiple(() =>
+			{
+				CanFilter(e => decimal.Truncate(e.EntityValue) > 1m);
+				CanSelect(e => decimal.Truncate(e.EntityValue));
+			});
+		}
+
 		private void CanFilter(Expression<Func<Entity, bool>> predicate)
 		{
 			using (ISession session = OpenSession())

src/NHibernate/Dialect/FirebirdDialect.cs

@@ -464,7 +464,7 @@ private void RegisterMathematicalFunctions()
 			RegisterFunction("rand", new NoArgSQLFunction("rand", NHibernateUtil.Double));
 			RegisterFunction("sign", new StandardSQLFunction("sign", NHibernateUtil.Int32));
 			RegisterFunction("sqtr", new StandardSQLFunction("sqtr", NHibernateUtil.Double));
-			RegisterFunction("truncate", new StandardSQLFunction("truncate"));
+			RegisterFunction("truncate", new StandardSQLFunction("trunc"));
 			RegisterFunction("floor", new StandardSQLFunction("floor"));
 			RegisterFunction("round", new StandardSQLFunction("round"));
 		}

src/NHibernate/Dialect/MySQLDialect.cs

@@ -261,8 +261,8 @@ protected virtual void RegisterFunctions()
 			RegisterFunction("ceiling", new StandardSQLFunction("ceiling"));
 			RegisterFunction("floor", new StandardSQLFunction("floor"));
 			RegisterFunction("round", new StandardSQLFunction("round"));
-			RegisterFunction("truncate", new StandardSQLFunction("truncate"));
-			
+			RegisterFunction("truncate", new SQLFunctionTemplate(null, "truncate(?1, 0)"));
+
 			RegisterFunction("rand", new NoArgSQLFunction("rand", NHibernateUtil.Double));
 
 			RegisterFunction("power", new StandardSQLFunction("power", NHibernateUtil.Double));

src/NHibernate/Linq/Functions/DefaultLinqToHqlGeneratorsRegistry.cs

@@ -59,6 +59,7 @@ public DefaultLinqToHqlGeneratorsRegistry()
 			this.Merge(new DecimalRemainderGenerator());
 			this.Merge(new DecimalNegateGenerator());
 			this.Merge(new RoundGenerator());
+			this.Merge(new TruncateGenerator());
 		}
 
 		protected bool GetRuntimeMethodGenerator(MethodInfo method, out IHqlGeneratorForMethod methodGenerator)

src/NHibernate/Linq/Functions/MathGenerator.cs

@@ -53,9 +53,6 @@ public MathGenerator()
 				ReflectHelper.GetMethodDefinition(() => Math.Ceiling(default(double))),
 				ReflectHelper.GetMethodDefinition(() => decimal.Ceiling(default(decimal))),
 
-				ReflectHelper.GetMethodDefinition(() => Math.Truncate(default(decimal))),
-				ReflectHelper.GetMethodDefinition(() => Math.Truncate(default(double))),
-
 				ReflectHelper.GetMethodDefinition(() => Math.Pow(default(double), default(double))),
 			};
 		}

src/NHibernate/Linq/Functions/TruncateGenerator.cs

@@ -0,0 +1,28 @@
+using System;
+using System.Collections.ObjectModel;
+using System.Linq.Expressions;
+using System.Reflection;
+using NHibernate.Hql.Ast;
+using NHibernate.Linq.Visitors;
+using NHibernate.Util;
+
+namespace NHibernate.Linq.Functions
+{
+    internal class TruncateGenerator : BaseHqlGeneratorForMethod
+	{
+		public TruncateGenerator()
+		{
+			SupportedMethods = new[]
+			{
+				ReflectHelper.GetMethodDefinition(() => Math.Truncate(default(decimal))),
+				ReflectHelper.GetMethodDefinition(() => Math.Truncate(default(double))),
+				ReflectHelper.GetMethodDefinition(() => decimal.Truncate(default(decimal)))
+			};
+		}
+
+		public override HqlTreeNode BuildHql(MethodInfo method, Expression expression, ReadOnlyCollection<Expression> arguments, HqlTreeBuilder treeBuilder, IHqlExpressionVisitor visitor)
+		{
+			return treeBuilder.MethodCall("truncate", visitor.Visit(arguments[0]).AsExpression());
+		}
+	}
+}