Merge pull request #26 from zolrath/Compare-Nullable

Allow comparing Nullable via Expression.Constant

Sieve/Services/SieveProcessor.cs

@@ -142,7 +142,7 @@ namespace Sieve.Services
                                                   ? converter.ConvertFrom(filterTerm.Value)
                                                   : Convert.ChangeType(filterTerm.Value, property.PropertyType);
 
-                        Expression filterValue = GetClosureOverConstant(constantVal);
+                        Expression filterValue = GetClosureOverConstant(constantVal, property.PropertyType);
 
                         dynamic propertyValue = Expression.PropertyOrField(parameterExpression, property.Name);
 
@@ -219,12 +219,13 @@ namespace Sieve.Services
             }
         }
 
-        //Workaround to ensure that the filter value gets passed as a parameter in generated SQL from EF Core
-        //See https://github.com/aspnet/EntityFrameworkCore/issues/3361
-        private Expression GetClosureOverConstant<T>(T constant)
+        // Workaround to ensure that the filter value gets passed as a parameter in generated SQL from EF Core
+        // See https://github.com/aspnet/EntityFrameworkCore/issues/3361
+        // Expression.Constant passed the target type to allow Nullable comparison
+        // See http://bradwilson.typepad.com/blog/2008/07/creating-nullab.html
+        private Expression GetClosureOverConstant<T>(T constant, Type targetType)
         {
-            Expression<Func<T>> closure = () => constant;
-            return closure.Body;
+            return Expression.Constant(constant, targetType);
         }
 
         private IQueryable<TEntity> ApplySorting<TEntity>(

SieveTests/Entities/Post.cs

@@ -1,4 +1,4 @@
-using System;
+using System;
 using System.ComponentModel.DataAnnotations.Schema;
 using Sieve.Attributes;
 
@@ -14,6 +14,7 @@ namespace SieveTests.Entities
         [Sieve(CanFilter = true, CanSort = true)]
         public int LikeCount { get; set; } = new Random().Next(0, 1000);
 
+
         [Sieve(CanFilter = true, CanSort = true)]
         public int CommentCount { get; set; } = new Random().Next(0, 1000);
 
@@ -23,5 +24,8 @@ namespace SieveTests.Entities
         [Sieve(CanFilter = true, CanSort = true)]
         [Column(TypeName = "datetime")]
         public DateTime DateLastViewed { get; set; } = DateTime.UtcNow;
+
+        [Sieve(CanFilter = true, CanSort = true)]
+        public int? CategoryId { get; set; } = new Random().Next(0, 4);
     }
 }

SieveTests/Migrations/20180127005347_Init.cs

@@ -17,7 +17,8 @@ namespace SieveTests.Migrations
                     CommentCount = table.Column<int>(nullable: false),
                     DateCreated = table.Column<DateTimeOffset>(nullable: false),
                     LikeCount = table.Column<int>(nullable: false),
-                    Title = table.Column<string>(nullable: true)
+                    Title = table.Column<string>(nullable: true),
+                    CategoryId = table.Column<int>(nullable: true)
                 },
                 constraints: table => table.PrimaryKey("PK_Posts", x => x.Id));
         }

SieveTests/Migrations/ApplicationDbContextModelSnapshot.cs

@@ -34,6 +34,8 @@ namespace SieveTests.Migrations
 
                     b.Property<int>("LikeCount");
 
+                    b.Property<int?>("CategoryId");
+
                     b.Property<string>("Title");
 
                     b.HasKey("Id");

SieveUnitTests/Entities/Post.cs

@@ -19,6 +19,9 @@ namespace SieveUnitTests.Entities
         [Sieve(CanFilter = true, CanSort = true)]
         public DateTimeOffset DateCreated { get; set; } = DateTimeOffset.UtcNow;
 
+        [Sieve(CanFilter = true, CanSort = true)]
+        public int? CategoryId { get; set; } = new Random().Next(0, 4);
+
         [Sieve(CanFilter = true, CanSort = true)]
         public bool IsDraft { get; set; }
 

SieveUnitTests/General.cs

@@ -1,4 +1,4 @@
-using System;
+using System;
 using System.Collections.Generic;
 using System.Linq;
 using Microsoft.VisualStudio.TestTools.UnitTesting;
@@ -28,24 +28,28 @@ namespace SieveUnitTests
                     Id = 0,
                     Title = "A",
                     LikeCount = 100,
-                    IsDraft = true
+                    IsDraft = true,
+                    CategoryId = null,
                 },
                 new Post() {
                     Id = 1,
                     Title = "B",
                     LikeCount = 50,
-                    IsDraft = false
+                    IsDraft = false,
+                    CategoryId = 1,
                 },
                 new Post() {
                     Id = 2,
                     Title = "C",
-                    LikeCount = 0
+                    LikeCount = 0,
+                    CategoryId = 1,
                 },
                 new Post() {
                     Id = 3,
                     Title = "D",
                     LikeCount = 3,
-                    IsDraft = true
+                    IsDraft = true,
+                    CategoryId = 2,
                 },
             }.AsQueryable();
         }
@@ -103,6 +107,19 @@ namespace SieveUnitTests
             Assert.AreEqual(result.First().Id, 0);
         }
 
+        [TestMethod]
+        public void CanFilterNullableInts()
+        {
+            var model = new SieveModel()
+            {
+                Filters = "CategoryId==1"
+            };
+
+            var result = _processor.Apply(model, _posts);
+
+            Assert.IsTrue(result.Count() == 2);
+        }
+
         [TestMethod]
         public void EqualsDoesntFailWithNonStringTypes()
         {