From 42e4544d795fbaf448edcaf9d7048ba7c3496f38 Mon Sep 17 00:00:00 2001
From: Shay Rojansky <roji@roji.org>
Date: Tue, 27 Feb 2018 11:57:54 +0200
Subject: [PATCH] Implement value comparer for hstore

Closes #306
---
 .../Mapping/NpgsqlHstoreTypeMapping.cs        | 30 ++++++++++++++++++-
 .../Storage/NpgsqlTypeMappingTest.cs          | 17 +++++++++++
 2 files changed, 46 insertions(+), 1 deletion(-)

diff --git a/src/EFCore.PG/Storage/Internal/Mapping/NpgsqlHstoreTypeMapping.cs b/src/EFCore.PG/Storage/Internal/Mapping/NpgsqlHstoreTypeMapping.cs
index 223aba284..a21eb1741 100644
--- a/src/EFCore.PG/Storage/Internal/Mapping/NpgsqlHstoreTypeMapping.cs
+++ b/src/EFCore.PG/Storage/Internal/Mapping/NpgsqlHstoreTypeMapping.cs
@@ -1,14 +1,21 @@
 using System;
 using System.Collections.Generic;
+using System.Linq.Expressions;
 using System.Net.NetworkInformation;
 using System.Text;
+using JetBrains.Annotations;
+using Microsoft.EntityFrameworkCore.ChangeTracking;
+using Microsoft.EntityFrameworkCore.ChangeTracking.Internal;
 using NpgsqlTypes;
 
 namespace Microsoft.EntityFrameworkCore.Storage.Internal.Mapping
 {
     public class NpgsqlHstoreTypeMapping : NpgsqlTypeMapping
     {
-        public NpgsqlHstoreTypeMapping() : base("hstore", typeof(Dictionary<string, string>), NpgsqlDbType.Hstore) {}
+        static readonly HstoreComparer ComparerInstance = new HstoreComparer();
+
+        public NpgsqlHstoreTypeMapping()
+            : base("hstore", typeof(Dictionary<string, string>), null, ComparerInstance, NpgsqlDbType.Hstore) {}
 
         protected override string GenerateNonNullSqlLiteral(object value)
         {
@@ -33,5 +40,26 @@ protected override string GenerateNonNullSqlLiteral(object value)
             sb.Append('\'');
             return sb.ToString();
         }
+
+        class HstoreComparer : ValueComparer<Dictionary<string, string>>
+        {
+            public HstoreComparer() : base(
+                (a, b) => Compare(a,b),
+                source => Snapshot(source))
+            {}
+
+            static bool Compare(Dictionary<string, string> a, Dictionary<string, string> b)
+            {
+                if (a.Count != b.Count)
+                    return false;
+                foreach (var kv in a)
+                    if (!b.TryGetValue(kv.Key, out var bValue) || kv.Value != bValue)
+                        return false;
+                return true;
+            }
+
+            static Dictionary<string, string> Snapshot(Dictionary<string, string> source)
+                => new Dictionary<string, string>(source);
+        }
     }
 }
diff --git a/test/EFCore.PG.Tests/Storage/NpgsqlTypeMappingTest.cs b/test/EFCore.PG.Tests/Storage/NpgsqlTypeMappingTest.cs
index e516f1b42..5b87cb87d 100644
--- a/test/EFCore.PG.Tests/Storage/NpgsqlTypeMappingTest.cs
+++ b/test/EFCore.PG.Tests/Storage/NpgsqlTypeMappingTest.cs
@@ -176,6 +176,23 @@ public void GenerateSqlLiteral_returns_hstore_literal()
                 { "k2", "v2" }
             }));
 
+        [Fact]
+        public void ValueComparer_hstore()
+        {
+            var source = new Dictionary<string, string>
+            {
+                { "k1", "v1"},
+                { "k2", "v2"}
+            };
+            
+            var comparer = GetMapping("hstore").Comparer;
+            var snapshot = (Dictionary<string, string>)comparer.SnapshotFunc(source);
+            Assert.Equal(source, snapshot);
+            Assert.True(comparer.CompareFunc(source, snapshot));
+            snapshot.Remove("k1");
+            Assert.False(comparer.CompareFunc(source, snapshot));
+        }
+
         [Fact]
         public void GenerateSqlLiteral_returns_jsonb_literal()
             => Assert.Equal(@"JSONB '{""a"":1}'", GetMapping("jsonb").GenerateSqlLiteral(@"{""a"":1}"));