isnull (issue #13)

Author: StefH

src/System.Linq.Dynamic.Core/ExpressionParser.cs

@@ -254,14 +254,16 @@ interface IEnumerableSignatures
         static readonly Expression FalseLiteral = Expression.Constant(false);
         static readonly Expression NullLiteral = Expression.Constant(null);
 
-        const string KEYWORD_IT = "it";
-        const string KEYWORD_PARENT = "parent";
-        const string KEYWORD_ROOT = "root";
         const string SYMBOL_IT = "$";
         const string SYMBOL_PARENT = "^";
         const string SYMBOL_ROOT = "~";
+
+        const string KEYWORD_IT = "it";
+        const string KEYWORD_PARENT = "parent";
+        const string KEYWORD_ROOT = "root";
         const string KEYWORD_IIF = "iif";
         const string KEYWORD_NEW = "new";
+        const string KEYWORD_ISNULL = "isnull";
 
         static Dictionary<string, object> _keywords;
 
@@ -448,6 +450,18 @@ Expression ParseNullCoalescing()
             return expr;
         }
 
+        // isnull(a,b) operator
+        Expression ParseIsNull()
+        {
+            int errorPos = _token.pos;
+            NextToken();
+            Expression[] args = ParseArgumentList();
+            if (args.Length != 2)
+                throw ParseError(errorPos, Res.IsNullRequiresTwoArgs);
+
+            return Expression.Coalesce(args[0], args[1]);
+        }
+
         // ||, or operator
         Expression ParseConditionalOr()
         {
@@ -1034,6 +1048,7 @@ Expression ParseIdentifier()
                 if (value == (object)SYMBOL_ROOT) return ParseRoot();
                 if (value == (object)KEYWORD_IIF) return ParseIif();
                 if (value == (object)KEYWORD_NEW) return ParseNew();
+                if (value == (object)KEYWORD_ISNULL) return ParseIsNull();
 
                 NextToken();
 
@@ -1785,11 +1800,7 @@ Expression PromoteExpression(Expression expr, Type type, bool exact)
             {
                 if (ce == NullLiteral)
                 {
-#if !(NETFX_CORE || DNXCORE50 || DOTNET5_4 || NETSTANDARD)
                     if (!type.GetTypeInfo().IsValueType || IsNullableType(type))
-#else
-                    if (!type.GetTypeInfo().IsValueType || IsNullableType(type))
-#endif
                         return Expression.Constant(null, type);
                 }
                 else
@@ -1807,6 +1818,10 @@ Expression PromoteExpression(Expression expr, Type type, bool exact)
                             case TypeCode.Int64:
                             case TypeCode.UInt64:
                                 value = ParseNumber(text, target);
+
+                                // Make sure an enum value stays an enum value
+                                if (target.IsEnum)
+                                    value = Enum.ToObject(target, value);
                                 break;
                             case TypeCode.Double:
                                 if (target == typeof(decimal)) value = ParseNumber(text, target);
@@ -2654,6 +2669,7 @@ static Dictionary<string, object> CreateKeywords()
             d.Add(SYMBOL_ROOT, SYMBOL_ROOT);
             d.Add(KEYWORD_IIF, KEYWORD_IIF);
             d.Add(KEYWORD_NEW, KEYWORD_NEW);
+            d.Add(KEYWORD_ISNULL, KEYWORD_ISNULL);
 
             foreach (Type type in _predefinedTypes.OrderBy(kvp => kvp.Value).Select(kvp => kvp.Key))
             {

src/System.Linq.Dynamic.Core/Res.cs

@@ -15,6 +15,7 @@ internal static class Res
         public const string NoParentInScope = "No 'parent' is in scope";
         public const string NoRootInScope = "No 'root' is in scope";
         public const string IifRequiresThreeArgs = "The 'iif' function requires three arguments";
+        public const string IsNullRequiresTwoArgs = "The 'isnull' function requires two arguments";
         public const string FirstExprMustBeBool = "The first expression must be of type 'Boolean'";
         public const string BothTypesConvertToOther = "Both of the types '{0}' and '{1}' convert to the other";
         public const string NeitherTypeConvertsToOther = "Neither of the types '{0}' and '{1}' converts to the other";

test/System.Linq.Dynamic.Core.Tests/ExpressionTests.cs

@@ -208,6 +208,46 @@ public void ExpressionTests_NullCoalescing()
             Assert.Equal(expectedResult3, result3b.ToDynamicArray<int>());
         }
 
+        [Fact]
+        public void ExpressionTests_IsNull_Simple()
+        {
+            //Arrange
+            var baseQuery = new int?[] { 1, 2, null, 3, 4 }.AsQueryable();
+            var expectedResult = new int[] { 1, 2, 0, 3, 4 };
+
+            // Act
+            var result1 = baseQuery.Select("isnull(it, 0)");
+
+            //Assert
+            Assert.Equal(expectedResult, result1.ToDynamicArray<int>());
+        }
+
+        [Fact]
+        public void ExpressionTests_IsNull_Complex()
+        {
+            //Arrange
+            var testModels = User.GenerateSampleModels(3, true);
+            testModels[0].NullableInt = null;
+            testModels[1].NullableInt = null;
+            testModels[2].NullableInt = 5;
+
+            var expectedResult1 = testModels.AsQueryable().Select(u => new { UserName = u.UserName, X = u.NullableInt ?? (3 * u.Income) }).Cast<object>().ToArray();
+            var expectedResult2 = testModels.AsQueryable().Where(u => (u.NullableInt ?? 10) == 10).ToArray();
+            var expectedResult3 = testModels.Select(m => m.NullableInt ?? 10).ToArray();
+
+            //Act
+            var result1 = testModels.AsQueryable().Select("new (UserName, isnull(NullableInt, (3 * Income)) as X)");
+            var result2 = testModels.AsQueryable().Where("isnull(NullableInt, 10) == 10");
+            var result3a = testModels.AsQueryable().Select("isnull(NullableInt, @0)", 10);
+            var result3b = testModels.AsQueryable().Select<int>("isnull(NullableInt, @0)", 10);
+
+            //Assert
+            Assert.Equal(expectedResult1.ToString(), result1.ToDynamicArray().ToString());
+            Assert.Equal(expectedResult2, result2.ToArray());
+            Assert.Equal(expectedResult3, result3a.ToDynamicArray<int>());
+            Assert.Equal(expectedResult3, result3b.ToDynamicArray<int>());
+        }
+
         [Fact]
         public void ExpressionTests_ConditionalOr1()
         {