Add test cases and cleanup last call site.

This merges in the work in #1663 and cleans up the convert a bit further.

Author: Nick Craver

Dapper/SqlMapper.GridReader.Async.cs

@@ -233,7 +233,7 @@ private async Task<IEnumerable<T>> ReadBufferedAsync<T>(int index, Func<IDataRea
                     var buffer = new List<T>();
                     while (index == gridIndex && await reader.ReadAsync(cancel).ConfigureAwait(false))
                     {
-                        buffer.Add((T)deserializer(reader));
+                        buffer.Add(ConvertTo<T>(deserializer(reader)));
                     }
                     return buffer;
                 }

Dapper/SqlMapper.GridReader.cs

@@ -3,6 +3,8 @@
 using System.Data;
 using System.Linq;
 using System.Globalization;
+using System.Runtime.CompilerServices;
+
 namespace Dapper
 {
     public static partial class SqlMapper
@@ -418,15 +420,13 @@ public void Dispose()
                 GC.SuppressFinalize(this);
             }
 
-            private static T ConvertTo<T>(object value)
+            [MethodImpl(MethodImplOptions.AggressiveInlining)]
+            private static T ConvertTo<T>(object value) => value switch
             {
-                if (value is null or DBNull)
-                    return default;
-                else if (value is T t)
-                    return t;
-                else
-                    return (T)Convert.ChangeType(value, Nullable.GetUnderlyingType(typeof(T)) ?? typeof(T), CultureInfo.InvariantCulture);
-            }
+                T typed => typed,
+                null or DBNull => default,
+                _ => (T)Convert.ChangeType(value, Nullable.GetUnderlyingType(typeof(T)) ?? typeof(T), CultureInfo.InvariantCulture),
+            };
         }
     }
 }

tests/Dapper.Tests/AsyncTests.cs

@@ -240,6 +240,16 @@ public async Task TestMultiAsync()
             }
         }
 
+        [Fact]
+        public async Task TestMultiConversionAsync()
+        {
+            using (SqlMapper.GridReader multi = await connection.QueryMultipleAsync("select Cast(1 as BigInt) Col1; select Cast(2 as BigInt) Col2").ConfigureAwait(false))
+            {
+                Assert.Equal(1, multi.ReadAsync<int>().Result.Single());
+                Assert.Equal(2, multi.ReadAsync<int>().Result.Single());
+            }
+        }
+
         [Fact]
         public async Task TestMultiAsyncViaFirstOrDefault()
         {

tests/Dapper.Tests/QueryMultipleTests.cs

@@ -31,6 +31,16 @@ public void TestQueryMultipleBuffered()
             }
         }
 
+        [Fact]
+        public void TestMultiConversion()
+        {
+            using (SqlMapper.GridReader multi = connection.QueryMultiple("select Cast(1 as BigInt) Col1; select Cast(2 as BigInt) Col2"))
+            {
+                Assert.Equal(1, multi.Read<int>().Single());
+                Assert.Equal(2, multi.Read<int>().Single());
+            }
+        }
+
         [Fact]
         public void TestQueryMultipleNonBufferedIncorrectOrder()
         {