Use single-row/single-result hint when possible

Dapper.Tests/Assert.cs

@@ -4,9 +4,9 @@ namespace Dapper.Tests
 {
     public static class Assert
     {
-        public static void IsEqualTo<T>(this T obj, T other)
+        public static void IsEqualTo<T>(this T expected, T actual)
         {
-            Xunit.Assert.Equal(obj, other);
+            Xunit.Assert.Equal(expected, actual);
         }
 
         public static void IsSequenceEqualTo<T>(this IEnumerable<T> obj, IEnumerable<T> other)

Dapper/SqlMapper.Async.cs

@@ -117,7 +117,7 @@ private static async Task<IEnumerable<T>> QueryAsync<T>(this IDbConnection cnn,
                 try
                 {
                     if (wasClosed) await ((DbConnection)cnn).OpenAsync(cancel).ConfigureAwait(false);
-                    reader = await cmd.ExecuteReaderAsync(wasClosed ? CommandBehavior.CloseConnection | CommandBehavior.SequentialAccess : CommandBehavior.SequentialAccess, cancel).ConfigureAwait(false);
+                    reader = await cmd.ExecuteReaderAsync(GetBehavior(wasClosed, CommandBehavior.SequentialAccess | CommandBehavior.SingleResult), cancel).ConfigureAwait(false);
 
                     var tuple = info.Deserializer;
                     int hash = GetColumnHash(reader);
@@ -179,7 +179,7 @@ private static async Task<T> QueryFirstOrDefaultAsync<T>(this IDbConnection cnn,
                 try
                 {
                     if (wasClosed) await ((DbConnection)cnn).OpenAsync(cancel).ConfigureAwait(false);
-                    reader = await cmd.ExecuteReaderAsync(wasClosed ? CommandBehavior.CloseConnection | CommandBehavior.SequentialAccess : CommandBehavior.SequentialAccess, cancel).ConfigureAwait(false);
+                    reader = await cmd.ExecuteReaderAsync(GetBehavior(wasClosed, CommandBehavior.SequentialAccess | CommandBehavior.SingleResult  | CommandBehavior.SingleRow), cancel).ConfigureAwait(false);
 
                     T result = default(T);
                     if(await reader.ReadAsync(cancel).ConfigureAwait(false))
@@ -547,7 +547,7 @@ private static async Task<int> ExecuteImplAsync(IDbConnection cnn, CommandDefini
             {
                 if (wasClosed) await ((DbConnection)cnn).OpenAsync(command.CancellationToken).ConfigureAwait(false);
                 using (var cmd = (DbCommand)command.SetupCommand(cnn, info.ParamReader))
-                using (var reader = await cmd.ExecuteReaderAsync(wasClosed ? CommandBehavior.CloseConnection | CommandBehavior.SequentialAccess : CommandBehavior.SequentialAccess, command.CancellationToken).ConfigureAwait(false))
+                using (var reader = await cmd.ExecuteReaderAsync(GetBehavior(wasClosed, CommandBehavior.SequentialAccess | CommandBehavior.SingleResult), command.CancellationToken).ConfigureAwait(false))
                 {
                     if (!command.Buffered) wasClosed = false; // handing back open reader; rely on command-behavior
                     var results = MultiMapImpl<TFirst, TSecond, TThird, TFourth, TFifth, TSixth, TSeventh, TReturn>(null, CommandDefinition.ForCallback(command.Parameters), map, splitOn, reader, identity, true);
@@ -594,7 +594,7 @@ private static async Task<IEnumerable<TReturn>> MultiMapAsync<TReturn>(this IDbC
             try {
                 if (wasClosed) await ((DbConnection)cnn).OpenAsync().ConfigureAwait(false);
                 using (var cmd = (DbCommand)command.SetupCommand(cnn, info.ParamReader))
-                using (var reader = await cmd.ExecuteReaderAsync(command.CancellationToken).ConfigureAwait(false)) {
+                using (var reader = await cmd.ExecuteReaderAsync(GetBehavior(wasClosed, CommandBehavior.SequentialAccess | CommandBehavior.SingleResult), command.CancellationToken).ConfigureAwait(false)) {
                     var results = MultiMapImpl<TReturn>(null, default(CommandDefinition), types, map, splitOn, reader, identity, true);
                     return command.Buffered ? results.ToList() : results;
                 }
@@ -644,7 +644,7 @@ public static async Task<GridReader> QueryMultipleAsync(this IDbConnection cnn,
             {
                 if (wasClosed) await ((DbConnection)cnn).OpenAsync(command.CancellationToken).ConfigureAwait(false);
                 cmd = (DbCommand)command.SetupCommand(cnn, info.ParamReader);
-                reader = await cmd.ExecuteReaderAsync(wasClosed ? CommandBehavior.CloseConnection | CommandBehavior.SequentialAccess : CommandBehavior.SequentialAccess, command.CancellationToken).ConfigureAwait(false);
+                reader = await cmd.ExecuteReaderAsync(GetBehavior(wasClosed, CommandBehavior.SequentialAccess), command.CancellationToken).ConfigureAwait(false);
 
                 var result = new GridReader(cmd, reader, identity, command.Parameters as DynamicParameters, command.AddToCache, command.CancellationToken);
                 wasClosed = false; // *if* the connection was closed and we got this far, then we now have a reader
@@ -721,7 +721,7 @@ private static async Task<IDataReader> ExecuteReaderImplAsync(IDbConnection cnn,
             {
                 cmd = (DbCommand)command.SetupCommand(cnn, paramReader);
                 if (wasClosed) await ((DbConnection)cnn).OpenAsync(command.CancellationToken).ConfigureAwait(false);
-                var reader = await cmd.ExecuteReaderAsync(wasClosed ? CommandBehavior.CloseConnection | CommandBehavior.SequentialAccess : CommandBehavior.SequentialAccess, command.CancellationToken).ConfigureAwait(false);
+                var reader = await cmd.ExecuteReaderAsync(GetBehavior(wasClosed, CommandBehavior.SequentialAccess), command.CancellationToken).ConfigureAwait(false);
                 wasClosed = false;
                 return reader;
             }

Dapper/SqlMapper.cs

@@ -697,6 +697,7 @@ public static GridReader QueryMultiple(this IDbConnection cnn, CommandDefinition
         {
             return QueryMultipleImpl(cnn, ref command);
         }
+
         private static GridReader QueryMultipleImpl(this IDbConnection cnn, ref CommandDefinition command)
         {
             object param = command.Parameters;
@@ -710,7 +711,7 @@ private static GridReader QueryMultipleImpl(this IDbConnection cnn, ref CommandD
             {
                 if (wasClosed) cnn.Open();
                 cmd = command.SetupCommand(cnn, info.ParamReader);
-                reader = cmd.ExecuteReader(wasClosed ? CommandBehavior.CloseConnection | CommandBehavior.SequentialAccess : CommandBehavior.SequentialAccess);
+                reader = cmd.ExecuteReader(GetBehavior(wasClosed, CommandBehavior.SequentialAccess));
 
                 var result = new GridReader(cmd, reader, identity, command.Parameters as DynamicParameters, command.AddToCache);
                 cmd = null; // now owned by result
@@ -749,7 +750,7 @@ private static IEnumerable<T> QueryImpl<T>(this IDbConnection cnn, CommandDefini
                 cmd = command.SetupCommand(cnn, info.ParamReader);
 
                 if (wasClosed) cnn.Open();
-                reader = cmd.ExecuteReader(wasClosed ? CommandBehavior.CloseConnection | CommandBehavior.SequentialAccess : CommandBehavior.SequentialAccess);
+                reader = cmd.ExecuteReader(GetBehavior(wasClosed, CommandBehavior.SequentialAccess | CommandBehavior.SingleResult));
                 wasClosed = false; // *if* the connection was closed and we got this far, then we now have a reader
                 // with the CloseConnection flag, so the reader will deal with the connection; we
                 // still need something in the "finally" to ensure that broken SQL still results
@@ -811,7 +812,7 @@ private static T QueryFirstOrDefaultImpl<T>(this IDbConnection cnn, ref CommandD
                 cmd = command.SetupCommand(cnn, info.ParamReader);
 
                 if (wasClosed) cnn.Open();
-                reader = cmd.ExecuteReader(wasClosed ? CommandBehavior.CloseConnection | CommandBehavior.SequentialAccess : CommandBehavior.SequentialAccess);
+                reader = cmd.ExecuteReader(GetBehavior(wasClosed, CommandBehavior.SequentialAccess | CommandBehavior.SingleResult | CommandBehavior.SingleRow));
                 wasClosed = false; // *if* the connection was closed and we got this far, then we now have a reader
 
                 T result = default(T);
@@ -1061,7 +1062,7 @@ public static IEnumerable<TReturn> Query<TReturn>(this IDbConnection cnn, string
                 {
                     ownedCommand = command.SetupCommand(cnn, cinfo.ParamReader);
                     if (wasClosed) cnn.Open();
-                    ownedReader = ownedCommand.ExecuteReader(wasClosed ? CommandBehavior.CloseConnection | CommandBehavior.SequentialAccess : CommandBehavior.SequentialAccess);
+                    ownedReader = ownedCommand.ExecuteReader(GetBehavior(wasClosed, CommandBehavior.SequentialAccess | CommandBehavior.SingleResult));
                     reader = ownedReader;
                 }
                 DeserializerState deserializer = default(DeserializerState);
@@ -1104,7 +1105,10 @@ public static IEnumerable<TReturn> Query<TReturn>(this IDbConnection cnn, string
                 }
             }
         }
-
+        private static CommandBehavior GetBehavior(bool close, CommandBehavior @default)
+        {
+            return close ? (@default | CommandBehavior.CloseConnection) : @default;
+        }
         static IEnumerable<TReturn> MultiMapImpl<TReturn>(this IDbConnection cnn, CommandDefinition command, Type[] types, Func<object[], TReturn> map, string splitOn, IDataReader reader, Identity identity, bool finalize)
         {
             if (types.Length < 1)
@@ -1126,7 +1130,7 @@ static IEnumerable<TReturn> MultiMapImpl<TReturn>(this IDbConnection cnn, Comman
                 {
                     ownedCommand = command.SetupCommand(cnn, cinfo.ParamReader);
                     if (wasClosed) cnn.Open();
-                    ownedReader = ownedCommand.ExecuteReader();
+                    ownedReader = ownedCommand.ExecuteReader(GetBehavior(wasClosed, CommandBehavior.SequentialAccess | CommandBehavior.SingleResult));
                     reader = ownedReader;
                 }
                 DeserializerState deserializer = default(DeserializerState);
@@ -2272,8 +2276,7 @@ private static IDataReader ExecuteReaderImpl(IDbConnection cnn, ref CommandDefin
             {
                 cmd = command.SetupCommand(cnn, paramReader);
                 if (wasClosed) cnn.Open();
-                if (wasClosed) commandBehavior |= CommandBehavior.CloseConnection;
-                var reader = cmd.ExecuteReader(commandBehavior);
+                var reader = cmd.ExecuteReader(GetBehavior(wasClosed, commandBehavior));
                 wasClosed = false; // don't dispose before giving it to them!
                 disposeCommand = false;
                 // note: command.FireOutputCallbacks(); would be useless here; parameters come at the **end** of the TDS stream