优化聚合回收dbcontext的代码

Author: xuejmnet

src/ShardingCore/Sharding/Enumerators/StreamMergeAsync/OneAtMostElementStreamMergeAsyncEnumerator.cs

@@ -8,6 +8,9 @@ namespace ShardingCore.Sharding.Enumerators.StreamMergeAsync
 {
     internal class OneAtMostElementStreamMergeAsyncEnumerator<T> : IStreamMergeAsyncEnumerator<T>
     {
+        /// <summary>
+        /// 因为启动的时候需要一次movenext所以这边将其设置为-1
+        /// </summary>
         private int _moveIndex = -1;
         private T _constantElement;
 

src/ShardingCore/Sharding/MergeEngines/Executors/Abstractions/AbstractExecutor.cs

@@ -90,10 +90,13 @@ private async Task<LinkedList<TResult>> ExecuteAsync0(bool async,
                 if (dataSourceSqlExecutorUnit.ConnectionMode == ConnectionModeEnum.CONNECTION_STRICTLY)
                 {
                     MergeParallelExecuteResult(result, routeQueryResults.Select(o => o.MergeResult), async);
-                    var dbContexts = routeQueryResults.Where(o=>o!=null).Select(o => o.DbContext).ToArray();
-                    foreach (var dbContext in dbContexts)
+                    foreach (var routeQueryResult in routeQueryResults)
                     {
-                        await streamMergeContext.DbContextDisposeAsync(dbContext);
+                        var dbContext = routeQueryResult.DbContext;
+                        if (dbContext != null)
+                        {
+                            await streamMergeContext.DbContextDisposeAsync(dbContext);
+                        }
                     }
                 }
                 else