Question of Ex0403- Multi-Table Modification

mms · July 7th, 2009, 03:06 AM

Hi,

I have a question of Ex0403.
When I add a new record, Here prompts the mistake.
whether "tableChanges != tableDeletes" should be "tableDeletes != null"?

Thanks!

In Page 136:
15. Modify the event handler for the Save Data button as follows:

Code:

private void sourceBindingNavigatorSaveItem_Click(object sender, EventArgs e)
{
    this.Validate();
    this.sourceBindingSource.EndEdit();
    this.storyBindingSource.EndEdit();
    
    // Save added / edited parent rows
    FolktaleDBDataSet.SourceDataTable tableChanges =
        folktaleDBDataSet.Source.GetChanges(
        DataRowState.Added | DataRowState.Modified)
        as FolktaleDBDataSet.SourceDataTable;
    if (tableChanges != null)
    {
        sourceTableAdapter.Update(tableChanges);
    }
 
    // Save child row modifications
    characterStoryTableAdapter.Update(folktaleDBDataSet.CharacterStory);
    storyLocationTableAdapter.Update(folktaleDBDataSet.StoryLocation);
    storyTableAdapter.Update(folktaleDBDataSet.Story);
 
    // Save deleted parent rows
    FolktaleDBDataSet.SourceDataTable tableDeletes =
        folktaleDBDataSet.Source.GetChanges(DataRowState.Deleted)
        as FolktaleDBDataSet.SourceDataTable;
    if (tableChanges != tableDeletes)
    {
        sourceTableAdapter.Update(tableDeletes);
    }
 
    // Accept changes
    folktaleDBDataSet.AcceptChanges();
    }

mms · July 21st, 2009, 10:00 PM

Page 219-220:

Code:

// Parent table additions and modifications.
DataTable dataTableAChanges1 = dataTableA.GetChanges(
    DataRowState.Added | DataRowState.Modified)
if (dataTableAChanges1 != null)
{
    adapterA.Update(dataTableAChanges1);
}
// Child table changes.
adapterB.Update(dataTableB);
 
// Parent table deletions.
DataTable dataTableAChanges2 = dataTableA.GetChanges(DataRowState.Deleted)
if (dataTableAChanges2 != null)
{
    adapterA.Update(dataTableAChanges2);
}
// Accept changes in parent table.
dataTableA.AcceptChanges();

Codes for these two contradictory.
I think that is the code "dataTableAChanges2 != null", code "tableChanges != tableDeletes" is wrong.

My explanation is correct? thanks!

peace95 · July 23rd, 2009, 07:24 AM

mms:
In my opinion, the difference between pages 136 and 219-220 is the difference in database structure. The DB structure on page 136 is Hierarchial in structure while the DB structure on pages 219-220 is Relational. The author maintains the process of modification or modifying the two different structures is the same:

Step 1: Add or Update changes to the Parent Table, but no deletes;
Step 2: Add, Update and Delete modifications to the Child Table;
Step 3: Make Deletions to the Parent Table;
Step 4: Then commit changes/updates to the Database.

The author notes on page 131 in Hierarchial Structure DB for modifications steps 2 and 3 are expanded and to proceed with caution. Due to the complex levels of the structure, one must save the all changes and deletions of the children, hence the if-statement:

if (tableChanges != tableDeletes)

Hope this helps