EF6 重试过程为 SqlQuery 命令引发“SqlParameter 已被另一个 SqlParameterCollection 包含”

Question

我正在尝试使用 DBExecutionStrategy 重试已超时的查询，但当超时发生时，我收到错误消息“SqlParameter 已被另一个 SqlParameterCollection 包含”。我正在使用 EF6。

我的查询：

using (var ctx = new EntityModel())
{
    IEnumerable<ItemResponse> items= ctx.Database.SqlQuery<ItemResponse>(
           "spItemListGet @UserID", new SqlParameter("@UserID", UserID)
    ).ToList();
}

我的执行策略：

protected override bool ShouldRetryOn(Exception ex)
{
    bool retry = false;

    SqlException sqlException = ex as SqlException;
    if (sqlException != null)
    {
        int[] errorsToRetry =
        {
            -2,     //Timeout
        };
        if (sqlException.Errors.Cast<SqlError>().Any(x => errorsToRetry.Contains(x.Number)))
        {
            retry = true;
        }
        else
        {
            throw ex; //dont retry
        }
    }

    return retry;
}

堆栈跟踪：

System.ArgumentException: The SqlParameter is already contained by another SqlParameterCollection.
   at System.Data.SqlClient.SqlParameterCollection.Validate(Int32 index, Object value)
   at System.Data.SqlClient.SqlParameterCollection.AddRange(Array values)
   at System.Data.Entity.Core.Objects.ObjectContext.CreateStoreCommand(String commandText, Object[] parameters)
   at System.Data.Entity.Core.Objects.ObjectContext.ExecuteStoreQueryInternal[TElement](String commandText, String entitySetName, ExecutionOptions executionOptions, Object[] parameters)
   at System.Data.Entity.Core.Objects.ObjectContext.<>c__DisplayClass65`1.<ExecuteStoreQueryReliably>b__64()
   at System.Data.Entity.Core.Objects.ObjectContext.ExecuteInTransaction[T](Func`1 func, IDbExecutionStrategy executionStrategy, Boolean startLocalTransaction, Boolean releaseConnectionOnSuccess)
   at System.Data.Entity.Core.Objects.ObjectContext.<>c__DisplayClass65`1.<ExecuteStoreQueryReliably>b__63()
   at System.Data.Entity.Infrastructure.DbExecutionStrategy.Execute[TResult](Func`1 operation)
   at System.Data.Entity.Core.Objects.ObjectContext.ExecuteStoreQueryReliably[TElement](String commandText, String entitySetName, ExecutionOptions executionOptions, Object[] parameters)
   at System.Data.Entity.Core.Objects.ObjectContext.ExecuteStoreQuery[TElement](String commandText, ExecutionOptions executionOptions, Object[] parameters)
   at System.Data.Entity.Internal.InternalContext.<>c__DisplayClass14`1.<ExecuteSqlQuery>b__13()
   at System.Data.Entity.Internal.LazyEnumerator`1.MoveNext()
   at System.Linq.Enumerable.WhereSelectEnumerableIterator`2.MoveNext()
   at System.Collections.Generic.List`1..ctor(IEnumerable`1 collection)
   at System.Linq.Enumerable.ToList[TSource](IEnumerable`1 source)

可以做些什么来防止这个错误？ Database.SqlQuery 可以和执行策略一起使用吗？

Answer 1

简短的回答：不，你不能这样做（如果你的命令有参数）。

长答案： 这是该问题的最小再现。我从图片中去掉了执行策略，并用循环伪造了它。此逻辑在ObjectContext 中实现，特别是在ExecuteStoreQueryInternalAsync 方法中。问题似乎是清理部分缺少command.Parameters.Clear() 调用。

static void Main(string[] args)
{
    TestQuery();
}

private static void TestQuery()
{
    using (var ctx = new ProductContext())
    {
        var parameter = new SqlParameter("@ID", 1);
        var commandText = "select * from product where ProductId = @ID";

        Action a = () =>
        {
            IDbCommand command = new SqlCommand();
            command.CommandText = commandText;
            command.Parameters.Add(parameter);

            command.Connection = ctx.Database.Connection;
            if (command.Connection.State != ConnectionState.Open)
            {
                command.Connection.Open();
            }

            var reader = command.ExecuteReader();
            try
            {
                throw new Exception();
                while (reader.Read())
                {
                    var pId = reader["ProductID"];
                }
                reader.Close();
            }
            catch (Exception exc)
            {
                //for simplification, we just swallow this error, but in reality the connection error
                //would reach the IDbExecutionStrategy, and would do a retry. Instead we fake the retry
                //with a loop below
            }
            finally
            {
                reader.Dispose();

                //command.Parameters.Clear();  <--------- THIS LINE IS MISSING FROM EF
                command.Dispose();
            }
        };

        for (int i = 0; i < 2; i++) // we fake the retry with a loop now
        {
            a();
        }
    }
}