Question

我正在使用EF6查询后端数据库。用户可以自定义临时表并从临时表中查询数据。我正在使用

DataTable result = context.Query(queryStatement);

获得结果，并且效果很好。

现在在大量其他sqlcommand中需要查询，并且需要事务。所以我有

public static DataTable GetData()
{
    using (MyDbContext context = new MyDbContext())
    using (DbContextTransaction tran = context.Database.BeginTransaction())
    {
        try
        {
            int rowAffected = context.Database.ExecuteSqlCommand(
                "UPDATE [MyDb].dbo.[TableLocks] SET RefCount = RefCount + 1 WHERE TableName = 'TESTTABLE1'");
            if (rowAffected != 1)
                throw new Exception("Cannot find 'TestTable1'");

            //The following line will raise an exception
            DataTable result = context.Query("SELECT TOP 100 * FROM [MyDb].dbo.[TestTable1]");
            //This line will work if I change it to 
            //context.Database.ExecuteSqlCommand("SELECT TOP 100 * FROM [MyDb].dbo.[TestTable1]");
            //but I don't know how to get the result out of it.
            context.Database.ExecuteSqlCommand(
                "UPDATE [MyDb].dbo.[TableLocks] SET RefCount = RefCount - 1 WHERE TableName = 'TestTable1'");
            tran.Commit();

            return result;
        }
        catch (Exception ex)
        {
            tran.Rollback();
            throw (ex);
        }
    }
}

但这会在执行context.Query时引发异常。

ExecuteReader requires the command to have a transaction when the connection 
assigned to the command is in a pending local transaction.  The Transaction 
property of the command has not been initialized.

当我阅读本文时：https://docs.microsoft.com/en-us/ef/ef6/saving/transactions 它说：

实体框架不会在查询中包装查询。

是引起此问题的原因吗？

如何在交易中使用context.Query()？

我还能使用什么？

我尝试了所有其他方法，但都不起作用-因为无法事先预测返回数据类型。

我刚刚意识到Query方法是在MyDbContext中定义的！

    public DataTable Query(string sqlQuery)
    {
        DbProviderFactory dbFactory = DbProviderFactories.GetFactory(Database.Connection);

        using (var cmd = dbFactory.CreateCommand())
        {
            cmd.Connection = Database.Connection;
            cmd.CommandType = CommandType.Text;
            cmd.CommandText = sqlQuery;
            using (DbDataAdapter adapter = dbFactory.CreateDataAdapter())
            {
                adapter.SelectCommand = cmd;

                DataTable dt = new DataTable();
                adapter.Fill(dt);

                return dt;
            }
        }
    }

Answer 1

可能是您缺少此部分-

您可以直接在 SqlConnection本身，或在DbContext上。所有这些操作都是在一笔交易中执行。您负责提交或回滚事务以及用于调用Dispose（）以及关闭和处置数据库连接

然后是此代码库-

using (var conn = new SqlConnection("..."))
{
    conn.Open();

    using (var sqlTxn = 
    conn.BeginTransaction(System.Data.IsolationLevel.Snapshot))
    {
        try
        {
            var sqlCommand = new SqlCommand();
            sqlCommand.Connection = conn;
            sqlCommand.Transaction = sqlTxn;
            sqlCommand.CommandText =
                       @"UPDATE Blogs SET Rating = 5" +
                        " WHERE Name LIKE '%Entity Framework%'";
            sqlCommand.ExecuteNonQuery();

            using (var context =  
                new BloggingContext(conn, contextOwnsConnection: false))
            {
                        context.Database.UseTransaction(sqlTxn);

                        var query =  context.Posts.Where(p => p.Blog.Rating >= 5);
                        foreach (var post in query)
                        {
                            post.Title += "[Cool Blog]";
                        }
                       context.SaveChanges();
                    }

                    sqlTxn.Commit();
        }
        catch (Exception)
        {
             sqlTxn.Rollback();
        }
    }
}

特别是这个-

context.Database.UseTransaction(sqlTxn);

Answer 2

对不起，如上所述，我认为Query方法来自EF，但是我检查了代码，发现它实际上是由MyDbContext类中定义的另一个开发人员编码的。由EF生成，我从不认为有人添加了一种方法。

是

public DataTable Query(string sqlQuery)
{
    DbProviderFactory dbFactory = DbProviderFactories.GetFactory(Database.Connection);

    using (var cmd = dbFactory.CreateCommand())
    {
        cmd.Connection = Database.Connection;
        cmd.CommandType = CommandType.Text;
        cmd.CommandText = sqlQuery;

        //And I added this line, then problem solved.
        if (Database.CurrentTransaction != null)
            cmd.Transaction = Database.CurrentTransaction.UnderlyingTransaction;

        using (DbDataAdapter adapter = dbFactory.CreateDataAdapter())
        {
            adapter.SelectCommand = cmd;

            DataTable dt = new DataTable();
            adapter.Fill(dt);

            return dt;
        }
    }
}

无法在事务内使用DbContext.Query

2 个答案: