具有Treeview更新的SQL数据读取器

Question

I have a table in SQL Express that contains some data used in TreeView type scenario.

It has parent-child relationship, but it is all in one table.

My aim is to set an indent level value, and my thinking was to select the data, use the reader to start off with first record. It has no parent so the level remains 0, if the record has a parent it must check the value of the indent of the parent and then add 1.

My problem is that all levels are 0 to start with, when it runs through my code, it sets the indent level to 1 on the second record, but when it gets to record three it show the level of parent of three is still 0. even though I updated it and when I look in the table it is set to 1. It seems that my select has already stored the data in the reader.

Table Structure:

using (SqlConnection connection = new SqlConnection("Data Source=" + servername + "; MultipleActiveResultSets = true;Initial Catalog=" + database + "; Integrated Security=SSPI"))
{
    using (SqlCommand cmd = new SqlCommand("SELECT * FROM relationship", connection))
    {
        connection.Open();

        using (SqlDataReader reader = cmd.ExecuteReader())
        {
            // Check is the reader has any rows at all before starting to read.
            if (reader.HasRows)
            {
                // Read advances to the next row.
                while (reader.Read())
                {
                    int sid = reader.GetInt32(1);

                    //GET THE CURRENT LEVEL OF THE RECORD
                    int slevel = reader.GetInt32(4); /* THIS SECTION IS NOT SELECTING THE CURRENT DATA THAT WAS UPDATED IN MY UPDATE BELOW*/

                    //ADD TO CURRENT LEVEL
                    int newslevel = slevel + 1;

                    MessageBox.Show("MY ID IS " + sid + " MY LEVEL IS " + slevel);

                    using (SqlCommand upd = new SqlCommand("UPDATE relationship SET level=@newlevel WHERE parent_id_ref=@sid", connection))
                    {
                        upd.Parameters.AddWithValue("@sid", sid);
                        upd.Parameters.AddWithValue("@newlevel", newslevel);
                        int rows = upd.ExecuteNonQuery();
                    }
                }
            }
        }
        connection.Close();
    }
}

Answer 1

That approach won't work. Your reader won't see updates performed by your updates.

An easy approach would be to do an iterative set of updates. say,

• Start with all levels to null
• bulk update level to 0 where "parent_id = parent_id_ref"

update relationship set level = 0 where parent_id = parent_id_ref

• bulk update children of any parent that already has their level set

update relationship set level = parent.level + 1
from relationship child inner join relationship parent on parent.parent_id = child.parent_id_ref
where parent.level is not null and child.level = 0

• repeat the the previous statement until the # of affected rows by one iteration is 0.

This could all be done in a single SQL command, with the loop around the final step checking the @@rowcount value after the statement