需要通过SQL表行进行迭代，每次一个（表过大，使用adapter.Fill） [英] Need to iterate through SQL table rows, one at a time (table too big to use adapter.Fill)

问题描述

这是很容易让我通过一个小SQL Server 2005的表像这样写着：

It's easy enough for me to read through a small SQL Server 2005 table like this:

string cmdText = "select * from myTable";
SqlDataAdapter adapter = new SqlDataAdapter(cmdText, connection);
DataTable table = new DataTable();
adapter.Fill(table);

不幸的是，这种方法似乎整个表加载到内存中，这根本是行不通的与我一起工作的巨大的表。

Unfortunately, this method appears to load the entire table into memory, which simply isn't going to work with the gigantic tables I'm working with.

我希望能够在同一时间通过表迭代一行，这样，只有一行必须在内存中一次。沿着线的东西：

I would like to be able to iterate through the table one row at a time, such that only one row needs to be in memory at once. Something along the lines of:

foreach (DataRow row in rowIteratorObject)
{
  // do something using the row

  // current row goes out of scope and is no longer in memory
}

的类似，您可以使用StreamReader的处理，而不是看它的所有在用一次，一次一个文本文件一行，顺便类。有谁知道的一种方式与表中的行做到这一点（或者，如果我找错了树，一种替代解决方案）？

Kind of similar to the way you can use StreamReader to deal with a text file one line at a time, instead of reading it all in at once. Does anyone know of a way to do this with table rows (or, if I'm barking up the wrong tree, an alternative solution)?

推荐答案

您应该使用DataReader：

You should use a DataReader:

using( var connection = new SqlConnection( "my connection string" ) ) {
    using( var command = connection.CreateCommand() ) {
        command.CommandText = "SELECT Column1, Column2, Column3 FROM myTable";

        connection.Open();
        using( var reader = command.ExecuteReader() ) {
            var indexOfColumn1 = reader.GetOrdinal( "Column1" );
            var indexOfColumn2 = reader.GetOrdinal( "Column2" );
            var indexOfColumn3 = reader.GetOrdinal( "Column3" );

            while( reader.Read() ) {
                var value1 = reader.GetValue( indexOfColumn1 );
                var value2 = reader.GetValue( indexOfColumn2 );
                var value3 = reader.GetValue( indexOfColumn3 );

                // now, do something what you want
            }
        }
        connection.Close();
    }
}

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