Null-coalescing operator support (#9)

Author: StefH

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

@@ -51,7 +51,8 @@ enum TokenId
             GreaterThanEqual,
             DoubleBar,
             DoubleGreaterThan,
-            DoubleLessThan
+            DoubleLessThan,
+            NullCoalescing
         }
 
         interface ILogicalSignatures
@@ -407,7 +408,7 @@ public IEnumerable<DynamicOrdering> ParseOrdering()
         Expression ParseExpression()
         {
             int errorPos = _token.pos;
-            Expression expr = ParseConditionalOr();
+            Expression expr = ParseNullCoalescing();
             if (_token.id == TokenId.Question)
             {
                 NextToken();
@@ -420,6 +421,19 @@ Expression ParseExpression()
             return expr;
         }
 
+        // ?? (null-coalescing) operator
+        Expression ParseNullCoalescing()
+        {
+            Expression expr = ParseConditionalOr();
+            if (_token.id == TokenId.NullCoalescing)
+            {
+                NextToken();
+                Expression right = ParseExpression();
+                expr = Expression.Coalesce(expr, right);
+            }
+            return expr;
+        }
+
         // ||, or operator
         Expression ParseConditionalOr()
         {
@@ -1383,11 +1397,16 @@ static string GetTypeName(Type type)
         static bool TryGetMemberName(Expression expression, out string memberName)
         {
             var memberExpression = expression as MemberExpression;
+            if (memberExpression == null && expression.NodeType == ExpressionType.Coalesce)
+            {
+                memberExpression = ((expression as BinaryExpression).Left) as MemberExpression;
+            }
             if (memberExpression != null)
             {
                 memberName = memberExpression.Member.Name;
                 return true;
             }
+
 #if NETFX_CORE
             var indexExpression = expression as IndexExpression;
             if (indexExpression != null && indexExpression.Indexer.DeclaringType == typeof(DynamicObjectClass))
@@ -2350,7 +2369,15 @@ void NextToken()
                     break;
                 case '?':
                     NextChar();
-                    t = TokenId.Question;
+                    if (_ch == '?')
+                    {
+                        NextChar();
+                        t = TokenId.NullCoalescing;
+                    }
+                    else
+                    {
+                        t = TokenId.Question;
+                    }
                     break;
                 case '[':
                     NextChar();

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

@@ -19,7 +19,7 @@ public class EntitiesTests : IDisposable
     {
         BlogContext _context;
 
-#region Entities Test Support
+        #region Entities Test Support
 
         static readonly Random Rnd = new Random(1);
 
@@ -77,9 +77,31 @@ void PopulateTestData(int blogCount = 25, int postCount = 10)
             _context.SaveChanges();
         }
 
-#endregion
+        #endregion
 
-#region Select Tests
+        #region Select Tests
+
+        [Fact]
+        public void Entities_Select_SingleColumn_NullCoalescing()
+        {
+            //Arrange
+            var blog1 = new Blog { BlogId = 1000, Name = "Blog1", NullableInt = null };
+            var blog2 = new Blog { BlogId = 2000, Name = "Blog2", NullableInt = 5 };
+            _context.Blogs.Add(blog1);
+            _context.Blogs.Add(blog2);
+            _context.SaveChanges();
+
+            var expected1 = _context.Blogs.Select(x => x.NullableInt ?? 10).ToArray();
+            var expected2 = _context.Blogs.Select(x => x.NullableInt ?? 9 + x.BlogId).ToArray();
+
+            //Act
+            var test1 = _context.Blogs.Select<int>("NullableInt ?? 10").ToArray();
+            var test2 = _context.Blogs.Select<int>("NullableInt ?? 9 + BlogId").ToArray();
+
+            //Assert
+            Assert.Equal(expected1, test1);
+            Assert.Equal(expected2, test2);
+        }
 
         [Fact]
         public void Entities_Select_SingleColumn()
@@ -106,7 +128,7 @@ public void Entities_Select_MultipleColumn()
 
             //Act
             var test = _context.Blogs.Select("new (\"x\" as X, BlogId, Name)").ToDynamicArray();
-            
+
             //Assert
             Assert.Equal(
                 expected,
@@ -156,9 +178,9 @@ public void Entities_Select_BlogPosts()
         //    }
         //}
 
-#endregion
+        #endregion
 
-#region GroupBy Tests
+        #region GroupBy Tests
 
         [Fact]
         public void Entities_GroupBy_SingleKey()
@@ -309,9 +331,9 @@ public void Entities_GroupBy_SingleKey_Sum()
             }
         }
 
-#endregion
+        #endregion
 
-#region Executor Tests
+        #region Executor Tests
 
         [Fact]
         public void FirstOrDefault_AsStringExpressions()
@@ -331,7 +353,7 @@ public void FirstOrDefault_AsStringExpressions()
             Assert.Equal(firstExpected.ToArray(), firstTest.ToArray());
         }
 
-#endregion
+        #endregion
     }
 }
 #endif

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

@@ -9,7 +9,33 @@ namespace System.Linq.Dynamic.Core.Tests
     public class ExpressionTests
     {
         [Fact]
-        public void ExpressionTests_ParseConditionalOr1()
+        public void ExpressionTests_NullCoalescing()
+        {
+            //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, NullableInt ?? (3 * Income) as X)");
+            var result2 = testModels.AsQueryable().Where("(NullableInt ?? 10) == 10");
+            var result3a = testModels.AsQueryable().Select("NullableInt ?? @0", 10);
+            var result3b = testModels.AsQueryable().Select<int>("NullableInt ?? @0", 10);
+
+            //Assert
+            Assert.Equal(expectedResult1.ToString(), result1.ToDynamicArray().ToString());
+            Assert.Equal(expectedResult2, result2.ToDynamicArray<User>());
+            Assert.Equal(expectedResult3, result3a.ToDynamicArray<int>());
+            Assert.Equal(expectedResult3, result3b.ToDynamicArray<int>());
+        }
+
+        [Fact]
+        public void ExpressionTests_ConditionalOr1()
         {
             //Arrange
             int[] values = { 1, 2, 3, 4, 5 };
@@ -24,7 +50,7 @@ public void ExpressionTests_ParseConditionalOr1()
         }
 
         [Fact]
-        public void ExpressionTests_ParseConditionalOr2()
+        public void ExpressionTests_ConditionalOr2()
         {
             //Arrange
             int[] values = { 1, 2, 3, 4, 5 };
@@ -39,7 +65,7 @@ public void ExpressionTests_ParseConditionalOr2()
         }
 
         [Fact]
-        public void ExpressionTests_ParseConditionalAnd1()
+        public void ExpressionTests_ConditionalAnd1()
         {
             //Arrange
             var values = new[] { new { s = "s", i = 1 }, new { s = "abc", i = 2 } };
@@ -54,7 +80,7 @@ public void ExpressionTests_ParseConditionalAnd1()
         }
 
         [Fact]
-        public void ExpressionTests_ParseConditionalAnd2()
+        public void ExpressionTests_ConditionalAnd2()
         {
             //Arrange
             var values = new[] { new { s = "s", i = 1 }, new { s = "abc", i = 2 } };

test/System.Linq.Dynamic.Core.Tests/Helpers/Entities/Blog.cs

@@ -6,6 +6,7 @@ public class Blog
     {
         public int BlogId { get; set; }
         public string Name { get; set; }
+        public int? NullableInt { get; set; }
 
         public virtual ICollection<Post> Posts { get; set; }
     }

test/System.Linq.Dynamic.Core.Tests/Helpers/Models/User.cs

@@ -8,6 +8,8 @@ public class User
 
         public string UserName { get; set; }
 
+        public int? NullableInt { get; set; }
+
         public int Income { get; set; }
 
         public UserProfile Profile { get; set; }