Is it recommended practice to include extension method within the static class itself?

I have:

public static class DataManager
{
    private s开发者_JAVA百科tatic Dictionary<string, DataTable> dataTables;

    //    extension method
    public static DataTable GetTable ( this string TableName )
    {
        return dataTables[ TableName ];
    }

}

I didn't want to expose the Dictionary collection, and this is the way I thought to accomplish this task. In my calling method:

DataTable GetTable (string TableName)
{
    return TableName.GetTable();
}

Is there another way I should, or could do this? Or is this acceptable?

I don't think that this is a good idea because, your method does not operate on a string (what the extension method would state), it operates on DataManager. So just use a static method in this case.