Make CommandBehavior more configurable; default to...

Make CommandBehavior more configurable; default to SingleRow=allowed,SingleResult=disallowed - but expose options; this fixes issues like #563 automatically, and allows the performance aspect  of #554 to be fixed via a global setting

Dapper/SqlMapper.Async.cs

@@ -218,7 +218,7 @@ public static Task<T> QuerySingleOrDefaultAsync<T>(this IDbConnection cnn, Comma
         private static Task<DbDataReader> ExecuteReaderWithFlagsFallbackAsync(DbCommand cmd, bool wasClosed, CommandBehavior behavior, CancellationToken cancellationToken)
         {
             var task = cmd.ExecuteReaderAsync(GetBehavior(wasClosed, behavior), cancellationToken);
-            if (task.Status == TaskStatus.Faulted && DisableCommandBehaviorOptimizations(behavior, task.Exception.InnerException))
+            if (task.Status == TaskStatus.Faulted && Settings.DisableCommandBehaviorOptimizations(behavior, task.Exception.InnerException))
             { // we can retry; this time it will have different flags
                 task = cmd.ExecuteReaderAsync(GetBehavior(wasClosed, behavior), cancellationToken);
             }

Dapper/SqlMapper.Settings.cs

-namespace Dapper
+using System;
+using System.Data;
+
+namespace Dapper
 {
     partial class SqlMapper
     {
@@ -7,6 +10,45 @@ partial class SqlMapper
         /// </summary>
         public static class Settings
         {
+            // disable single result by default; prevents errors AFTER the select being detected properly
+            const CommandBehavior DefaultAllowedCommandBehaviors = ~CommandBehavior.SingleResult;
+            internal static CommandBehavior AllowedCommandBehaviors { get; private set; } = DefaultAllowedCommandBehaviors;
+            private static void SetAllowedCommandBehaviors(CommandBehavior behavior, bool enabled)
+            {
+                if (enabled) AllowedCommandBehaviors |= behavior;
+                else AllowedCommandBehaviors &= ~behavior;
+            }
+            /// <summary>
+            /// Gets or sets whether dapper should use the CommandBehavior.SingleResult optimization
+            /// </summary>
+            public static bool UseSingleResultOptimization
+            {
+                get { return (AllowedCommandBehaviors & CommandBehavior.SingleResult) != 0; }
+                set { SetAllowedCommandBehaviors(CommandBehavior.SingleResult, value); }
+            }
+            /// <summary>
+            /// Gets or sets whether dapper should use the CommandBehavior.SingleRow optimization
+            /// </summary>
+            public static bool UseSingleRowOptimization
+            {
+                get { return (AllowedCommandBehaviors & CommandBehavior.SingleRow) != 0; }
+                set { SetAllowedCommandBehaviors(CommandBehavior.SingleRow, value); }
+            }
+            internal static bool DisableCommandBehaviorOptimizations(CommandBehavior behavior, Exception ex)
+            {
+                if (AllowedCommandBehaviors == DefaultAllowedCommandBehaviors
+                    && (behavior & (CommandBehavior.SingleResult | CommandBehavior.SingleRow)) != 0)
+                {
+                    if (ex.Message.Contains(nameof(CommandBehavior.SingleResult))
+                        || ex.Message.Contains(nameof(CommandBehavior.SingleRow)))
+                    { // some providers just just allow these, so: try again without them and stop issuing them
+                        SetAllowedCommandBehaviors(CommandBehavior.SingleResult | CommandBehavior.SingleRow, false);
+                        return true;
+                    }
+                }
+                return false;
+            }
+
             static Settings()
             {
                 SetDefaults();

Dapper/SqlMapper.cs

@@ -235,9 +235,7 @@ private static void ResetTypeHandlers(bool clone)
 #endif
             AddTypeHandlerImpl(typeof(XmlDocument), new XmlDocumentHandler(), clone);
             AddTypeHandlerImpl(typeof(XDocument), new XDocumentHandler(), clone);
-            AddTypeHandlerImpl(typeof(XElement), new XElementHandler(), clone);
-
-            allowedCommandBehaviors = DefaultAllowedCommandBehaviors;
+            AddTypeHandlerImpl(typeof(XElement), new XElementHandler(), clone);
         }
 #if !COREFX
         [MethodImpl(MethodImplOptions.NoInlining)]
@@ -912,7 +910,7 @@ private static IDataReader ExecuteReaderWithFlagsFallback(IDbCommand cmd, bool w
             }
             catch (ArgumentException ex)
             { // thanks, Sqlite!
-                if (DisableCommandBehaviorOptimizations(behavior, ex))
+                if (Settings.DisableCommandBehaviorOptimizations(behavior, ex))
                 {
                     // we can retry; this time it will have different flags
                     return cmd.ExecuteReader(GetBehavior(wasClosed, behavior));
@@ -1324,25 +1322,10 @@ public static IEnumerable<TReturn> Query<TReturn>(this IDbConnection cnn, string
                 }
             }
         }
-        const CommandBehavior DefaultAllowedCommandBehaviors = ~((CommandBehavior)0);
-        static CommandBehavior allowedCommandBehaviors = DefaultAllowedCommandBehaviors;
-        private static bool DisableCommandBehaviorOptimizations(CommandBehavior behavior, Exception ex)
-        {
-            if(allowedCommandBehaviors == DefaultAllowedCommandBehaviors
-                && (behavior & (CommandBehavior.SingleResult | CommandBehavior.SingleRow)) != 0)
-            {
-                if (ex.Message.Contains(nameof(CommandBehavior.SingleResult))
-                    || ex.Message.Contains(nameof(CommandBehavior.SingleRow)))
-                { // some providers just just allow these, so: try again without them and stop issuing them
-                    allowedCommandBehaviors = ~(CommandBehavior.SingleResult | CommandBehavior.SingleRow);
-                    return true;
-                }
-            }
-            return false;
-        }
+
         private static CommandBehavior GetBehavior(bool close, CommandBehavior @default)
         {
-            return (close ? (@default | CommandBehavior.CloseConnection) : @default) & allowedCommandBehaviors;
+            return (close ? (@default | CommandBehavior.CloseConnection) : @default) & Settings.AllowedCommandBehaviors;
         }
         static IEnumerable<TReturn> MultiMapImpl<TReturn>(this IDbConnection cnn, CommandDefinition command, Type[] types, Func<object[], TReturn> map, string splitOn, IDataReader reader, Identity identity, bool finalize)
         {