Support get-only C# 6 properties, i.e. public int Id {get;}

Author: mgravell

Dapper.Tests/Dapper.Tests.xproj

@@ -14,7 +14,9 @@
   <PropertyGroup>
     <SchemaVersion>2.0</SchemaVersion>
   </PropertyGroup>
-  <PropertyGroup Condition="'$(Configuration)|$(Platform)'=='Debug|AnyCPU'" />
+  <PropertyGroup Condition="'$(Configuration)|$(Platform)'=='Debug|AnyCPU'">
+    <ProduceOutputsOnBuild>True</ProduceOutputsOnBuild>
+  </PropertyGroup>
   <ItemGroup>
     <Service Include="{82a7f48d-3b50-4b1e-b82e-3ada8210c358}" />
   </ItemGroup>

Dapper.Tests/Tests.cs

@@ -3696,5 +3696,17 @@ protected static SqliteConnection GetSqliteConnection(bool open = true)
             return connection;
         }
 #endif
-            }
+        [Fact]
+        public void GetOnlyProperties()
+        {
+            var obj = connection.QuerySingle<HazGetOnly>("select 42 as [Id], 'def' as [Name];");
+            obj.Id.IsEqualTo(42);
+            obj.Name.IsEqualTo("def");
+        }
+        class HazGetOnly
+        {
+            public int Id { get; }
+            public string Name { get; } = "abc";
+        }
+    }
 }

Dapper/DefaultTypeMap.cs

@@ -164,13 +164,25 @@ public SqlMapper.IMemberMap GetMember(string columnName)
             if (property != null)
                 return new SimpleMemberMap(columnName, property);
 
+            // roslyn automatically implemented properties, in particular for get-only properties: <{Name}>k__BackingField;
+            var backingFieldName = $"<{columnName}>k__BackingField";
+
+            // preference order is:
+            // exact match over underscre match, backing fields over regular fields, exact case over wrong case
             var field = _fields.FirstOrDefault(p => string.Equals(p.Name, columnName, StringComparison.Ordinal))
-               ?? _fields.FirstOrDefault(p => string.Equals(p.Name, columnName, StringComparison.OrdinalIgnoreCase));
+               ?? _fields.FirstOrDefault(p => string.Equals(p.Name, columnName, StringComparison.OrdinalIgnoreCase))
+               ?? _fields.FirstOrDefault(p => string.Equals(p.Name, backingFieldName, StringComparison.Ordinal))
+               ?? _fields.FirstOrDefault(p => string.Equals(p.Name, backingFieldName, StringComparison.OrdinalIgnoreCase));
 
             if (field == null && MatchNamesWithUnderscores)
             {
-                field = _fields.FirstOrDefault(p => string.Equals(p.Name, columnName.Replace("_", ""), StringComparison.Ordinal))
-                    ?? _fields.FirstOrDefault(p => string.Equals(p.Name, columnName.Replace("_", ""), StringComparison.OrdinalIgnoreCase));
+                var effectiveColumnName = columnName.Replace("_", "");
+                backingFieldName = $"<{effectiveColumnName}>k__BackingField";
+
+                field = _fields.FirstOrDefault(p => string.Equals(p.Name, effectiveColumnName, StringComparison.Ordinal))
+                    ?? _fields.FirstOrDefault(p => string.Equals(p.Name, effectiveColumnName, StringComparison.OrdinalIgnoreCase))
+                    ?? _fields.FirstOrDefault(p => string.Equals(p.Name, backingFieldName, StringComparison.Ordinal))
+                    ?? _fields.FirstOrDefault(p => string.Equals(p.Name, backingFieldName, StringComparison.OrdinalIgnoreCase));
             }
 
             if (field != null)

Dapper/SqlMapper.cs

@@ -2798,7 +2798,7 @@ private static Func<IDataReader, object> GetTypeDeserializerImpl(
         )
         {
             var returnType = type.IsValueType() ? typeof(object) : type;
-            var dm = new DynamicMethod($"Deserialize{Guid.NewGuid()}", returnType, new[] { typeof(IDataReader) }, true);
+            var dm = new DynamicMethod($"Deserialize{Guid.NewGuid()}", returnType, new[] { typeof(IDataReader) }, type, true);
             var il = dm.GetILGenerator();
             il.DeclareLocal(typeof(int));
             il.DeclareLocal(type);