Chapter 9 use a dataadapter to add a record

ksackel · January 6th, 2017, 07:33 AM

Codelab on p385 and p386 is below.
The data from the person table is extracted into a DataSet obj via the Fill command. DS at this point would contain all the records of the person table
da.Fill(ds, "Person");

We then add a new row to the DS.
DataRow newRow = ds.Tables[0].NewRow();
newRow["FirstName"] = "Jack";
newRow["Surname"] = "Johnson";
ds.Tables[0].Rows.Add(newRow);

My question is a confirmation. i assume ds.tables[0].Rows.Add(newRow) must clear the contents of the DS and add one row (jane doe). As the update command da.update(ds.TAbles[0]) inserts all of the rows in DS to the database.
CAn you please confirm this or explain otherwise. i am failing to understand how the DS suddenly contains all the data and then after those adding row statements it is reduced to a single record.

Rod Stephens · January 7th, 2017, 01:58 PM

Hi Ksackel. Sorry for the slow reply. I was hoping the author of that chapter would respond (so I would have to think

).

The short answer is no, when you add a new record to it the DataSet still holds all of the other records.

Here's the longish explanation.

When you add a new record to a DataSet, the old records are still in it. Each rows has a state that records whether it is the original data loaded from the database, modified, added, or deleted.

You can see the records' statuses by looking at the row's State property. For example:

ds.Tables[0].Rows[5].RowState

When you add the new record, it is marked as new.

When you use Update to save changes to the database, the data adapter copies any changes (adds, deletes, or changes) back to the database.

It doesn't touch the unmodified records because they haven't changed. That can save a ton of time. For example, suppose you have 5,000 records but you only changed 1.

It then changes the state of all of the modified records to Unchanged to show that the data set is up to date with the database.

I hope that helps. Reply if it doesn't make sense.