修复last的bug

src/ShardingCore/Sharding/MergeEngines/EnumeratorStreamMergeEngines/Enumerables/LastOrDefaultStreamEnumerable.cs

@@ -20,7 +20,7 @@ namespace ShardingCore.Sharding.MergeEngines.EnumeratorStreamMergeEngines.Enumer
 
         protected override IExecutor<IStreamMergeAsyncEnumerator<TEntity>> CreateExecutor0(bool async)
         {
-            return new DefaultEnumeratorExecutor<TEntity>(GetStreamMergeContext(), GetStreamMergeCombine(), async);
+            return new LastOrDefaultEnumeratorExecutor<TEntity>(GetStreamMergeContext(), GetStreamMergeCombine(), async);
         }
     }
 }

src/ShardingCore/Sharding/MergeEngines/EnumeratorStreamMergeEngines/EnumeratorStreamMergeEngineFactory.cs

@@ -80,11 +80,7 @@ namespace ShardingCore.Sharding.MergeEngines.EnumeratorStreamMergeEngines
                     return new SingleOrDefaultStreamEnumerable<TEntity>(_streamMergeContext);
                 case nameof(Enumerable.Last):
                 case nameof(Enumerable.LastOrDefault):
-                {
-                    _streamMergeContext.ReSetSkip(0);
-                    _streamMergeContext.ReverseOrder();
                     return new LastOrDefaultStreamEnumerable<TEntity>(_streamMergeContext);
-                }
             }
 
             //未开启系统分表或者本次查询涉及多张分表

src/ShardingCore/Sharding/MergeEngines/Executors/Enumerators/LastOrDefaultEnumeratorExecutor.cs

@@ -0,0 +1,52 @@
+using System.Linq;
+using System.Threading;
+using System.Threading.Tasks;
+using ShardingCore.Extensions;
+using ShardingCore.Sharding.Enumerators;
+using ShardingCore.Sharding.Enumerators.StreamMergeAsync;
+using ShardingCore.Sharding.MergeEngines.Abstractions;
+using ShardingCore.Sharding.MergeEngines.Common;
+using ShardingCore.Sharding.MergeEngines.Executors.Enumerators.Abstractions;
+
+namespace ShardingCore.Sharding.MergeEngines.Executors.Enumerators
+{
+internal class LastOrDefaultEnumeratorExecutor<TResult> : AbstractEnumeratorExecutor<TResult>
+    {
+        private readonly IStreamMergeCombine _streamMergeCombine;
+        private readonly bool _async;
+
+        public LastOrDefaultEnumeratorExecutor(StreamMergeContext streamMergeContext, IStreamMergeCombine streamMergeCombine, bool async) : base(streamMergeContext)
+        {
+            _streamMergeCombine = streamMergeCombine;
+            _async = async;
+        }
+
+        protected override IStreamMergeCombine GetStreamMergeCombine()
+        {
+            return _streamMergeCombine;
+        }
+
+        public override IStreamMergeAsyncEnumerator<TResult> CombineInMemoryStreamMergeAsyncEnumerator(
+            IStreamMergeAsyncEnumerator<TResult>[] streamsAsyncEnumerators)
+        {
+            if (GetStreamMergeContext().IsPaginationQuery())
+                return new PaginationStreamMergeAsyncEnumerator<TResult>(GetStreamMergeContext(), streamsAsyncEnumerators, 0, GetStreamMergeContext().GetPaginationReWriteTake());//内存聚合分页不可以直接获取skip必须获取skip+take的数目
+            return base.CombineInMemoryStreamMergeAsyncEnumerator(streamsAsyncEnumerators);
+        }
+
+        protected override async Task<ShardingMergeResult<IStreamMergeAsyncEnumerator<TResult>>> ExecuteUnitAsync(SqlExecutorUnit sqlExecutorUnit, CancellationToken cancellationToken = new CancellationToken())
+        {
+            var streamMergeContext = GetStreamMergeContext();
+            streamMergeContext.ReverseOrder();
+            streamMergeContext.ReSetSkip(0);
+            var connectionMode = streamMergeContext.RealConnectionMode(sqlExecutorUnit.ConnectionMode);
+
+            var shardingDbContext = streamMergeContext.CreateDbContext(sqlExecutorUnit.RouteUnit, connectionMode);
+            var newQueryable = (IQueryable<TResult>)streamMergeContext.GetReWriteQueryable().RemoveAnyOrderBy().OrderWithExpression(streamMergeContext.Orders)
+                .ReplaceDbContextQueryable(shardingDbContext);
+
+            var streamMergeAsyncEnumerator = await AsyncParallelEnumerator(newQueryable, _async, cancellationToken);
+            return new ShardingMergeResult<IStreamMergeAsyncEnumerator<TResult>>(shardingDbContext, streamMergeAsyncEnumerator);
+        }
+    }
+}