chapter 9 update and delete records using dataadapter

ksackel · January 6th, 2017, 07:44 AM

Using codelab p387
we have prepopulated the da with update and delete commands via:
da.UpdateCommand = update;
da.DeleteCommand = delete;

what is the effect of the below. We have made modifications to the DS including updating the first row (ds.Tables[0].Rows[0]["FirstName"] = "Jack";) and deleting the second row(ds.Tables[0].Rows[1].Delete();).
What are we updating to the database via this command. i understand we are running update and delete sql statements but what are they ?
da.Update(ds.Tables[0]);

ksackel · January 6th, 2017, 07:48 AM

is the effect of the da.Update(ds.Tables[0]); only to update the first record to Jack Johnson and delete the second record????????? what about all the other records in the DataSet?

Rod Stephens · January 7th, 2017, 02:01 PM

See my reply to your earlier thread. The Update method uses the insert, updated, and delete command objects to update any records that are out of sync with the values in the database. It adds new records, updates modified ones, and removes deleted records.

Any records that have not been changed in the data set are not touched in the database to reduce the amount of data that must be transmitted back to the database server.

Again, reply if that doesn't make sense.

Rod Stephens · January 7th, 2017, 02:10 PM

Sorry, I missed this part:

Quote:

i understand we are running update and delete sql statements but what are they ?

The short answer is that the command objects (like the insert object) tell the data adapter how to insert, update, and delete data in the database.

This example sets the command text for the objects. For example, the insert command's text is:

Code:

INSERT INTO Students (FirstName, LastName)
VALUES (@FirstName, @LastName)

Then the code adds parameters that define the fields @FirstName and @LastName.

When you update the database, the command object basically loops through the new records, replaces @FirstName and @LastName with the record's values in the INSERT statement, and executes it. After the replacements, the command strings are something that the database can understand so it takes the necessary action, in this case inserting the records.

The update and delete objects (if they are present) do something similar.

You can also use command builders to make the commands slightly more automatically. See https://msdn.microsoft.com/en-us/lib...v=vs.110).aspx for more on that.