Question

I am trying to learn about how to work with databases in C# and I have gotten to a part in a tutorial when I have to work with DataSet , SqlDataAdapter and SqlCommandBuilder.This is the code I wrote in the example in the tutorial:

 public void InitData() {
        //instantiate the connection
        conn = new SqlConnection("Data Source=.\\SQLEXPRESS;AttachDbFilename=\"D:\\Projects IDE\\Visual Studio\\Exercitii\\Console.app\\WindowsFormsApplication1\\WindowsFormsApplication1\\PlanetWrox.mdf\";Integrated Security=True;User Instance=True");

        //1.instantiate a new DataSet
        dsCustomers = new DataSet();

        //2.init SqlDataAdapter with select command and connection
        daCustomers = new SqlDataAdapter("SELECT Id ,Name, SortOrder FROM Genre", conn);

        // 3. fill in insert, update, and delete commands
        SqlCommandBuilder cmdBldr = new SqlCommandBuilder(daCustomers);

        // 4. fill the dataset
        daCustomers.Fill(dsCustomers, tableName);
    }

    public void btnUpdateClicked(object sender, EventArgs e) {
        // write changes back to DataBase
        daCustomers.Update(dsCustomers, tableName);

    }   

There are a couple of things I do not understand here:

The first thing I noticed is that I do not have to open and close the database.From what limited knoledge I have about databases I know that in order to acces the data you have to open a connection to it and after you are done you have to close it.This must happen somewhere behind the scene.Is that righT? If that is so witch method does that?

The second question is regarding the SqlDataAdapter and SqlCommandBuilder.I do not understand what does SqlCommandBuilder does here.Isen’t the SqlDataAdapter the one that is executing the sql query?

Answer 1

The first thing I noticed is that I do not have to open and close the
database.

SqldataAdapter.Fill will open/close the connection for you.

If the IDbConnection is closed before Fill is called, it is opened to
retrieve data and then closed. If the connection is open before Fill
is called, it remains open.

The SqlCommandBuilder generates INSERT, UPDATE, or DELETE statements from the metadata of your provided select-statement. On this way you can call daCustomers.Update and all changes made to the DataSet will automatically be updated in the database.