Fix hstore SQL literal generation for null and escaped values

src/EFCore.PG/Storage/Internal/Mapping/NpgsqlHstoreTypeMapping.cs

@@ -66,29 +66,36 @@ protected override RelationalTypeMapping Clone(RelationalTypeMappingParameters p
     protected override string GenerateNonNullSqlLiteral(object value)
     {
         var sb = new StringBuilder("HSTORE '");
-        foreach (var kv in (IReadOnlyDictionary<string, string?>)value)
+
+        if (value is not IReadOnlyDictionary<string, string?> dict)
         {
-            sb.Append('"');
-            sb.Append(kv.Key); // TODO: Escape
-            sb.Append("\"=>");
-            if (kv.Value is null)
-            {
-                sb.Append("NULL");
-            }
-            else
-            {
-                sb.Append('"');
-                sb.Append(kv.Value); // TODO: Escape
-                sb.Append("\",");
-            }
+            throw new ArgumentException($"Expected a dictionary, but got {value.GetType()}", nameof(value));
         }
 
-        sb.Remove(sb.Length - 1, 1);
+        foreach (var kv in dict)
+        {
+            sb.Append(QuoteHStoreString(kv.Key));
+            sb.Append("=>");
+            sb.Append(kv.Value is null ? "NULL" : QuoteHStoreString(kv.Value));
+            sb.Append(',');
+        }
+
+        if (sb[^1] == ',')
+        {
+            sb.Remove(sb.Length - 1, 1);
+        }
 
         sb.Append('\'');
         return sb.ToString();
     }
 
+    // Quote string for use in an HStore literal.
+    // Escape \ as \\
+    // Escape " as \"
+    // Escape ' as ''
+    private static string QuoteHStoreString(string s)
+        => string.Concat("\"", s.Replace("\\", "\\\\").Replace("\"", "\\\"").Replace("'", "''"), "\"");
+
     private static ValueComparer? GetComparer(Type clrType)
     {
         if (clrType == typeof(Dictionary<string, string>))

test/EFCore.PG.Tests/Storage/NpgsqlTypeMappingTest.cs

@@ -454,6 +454,29 @@ public void GenerateSqlLiteral_returns_hstore_literal()
             """HSTORE '"k1"=>"v1","k2"=>"v2"'""",
             GetMapping("hstore").GenerateSqlLiteral(new Dictionary<string, string> { { "k1", "v1" }, { "k2", "v2" } }));
 
+    [Fact]
+    public void GenerateSqlLiteral_returns_hstore_literal_when_first_value_is_null()
+        => Assert.Equal(
+            """HSTORE '"k1"=>NULL,"k2"=>"v2"'""",
+            GetMapping("hstore").GenerateSqlLiteral(new Dictionary<string, string> { { "k1", null }, { "k2", "v2" } }));
+
+    [Fact]
+    public void GenerateSqlLiteral_returns_hstore_literal_with_escaped_keys_and_values()
+        => Assert.Equal(
+            """HSTORE '"k\"1\""=>"v\"1\"","k\\2"=>"v\\2","k''3''"=>"v''3''"'""",
+            GetMapping("hstore").GenerateSqlLiteral(new Dictionary<string, string>
+            {
+                { "k\"1\"", "v\"1\"" },
+                { "k\\2", "v\\2" },
+                { "k'3'", "v'3'" }
+            }));
+
+    [Fact]
+    public void GenerateSqlLiteral_returns_hstore_literal_from_empty_dictionary()
+        => Assert.Equal(
+            "HSTORE ''",
+            GetMapping("hstore").GenerateSqlLiteral(new Dictionary<string, string>()));
+
     [Fact]
     public void GenerateSqlLiteral_returns_BigInteger_literal()
     {