Do I need to perform a fill before an update in ADO.NET?

Question

This may seem trivial but every example I've ever seen of ADO.net almost always has a 'fill' before an 'update'. We really don't want to fill a dataset that may have 1000's of blobs, we just want to add(insert) to the table. Is fill required for an update?As an example here's sample code from MSFT's web site (we're doing something similar):

SqlConnection con = new SqlConnection("Server=Darkover;uid=<username>;pwd=<strong            password>;database=northwind");
SqlDataAdapter da = new SqlDataAdapter("Select * From MyImages", con);
SqlCommandBuilder MyCB = new SqlCommandBuilder(da); // What does this even do?
DataSet ds = new DataSet("MyImages");

da.MissingSchemaAction = MissingSchemaAction.AddWithKey;
FileStream fs = new FileStream(@"C:\winnt\Gone Fishing.BMP", FileMode.OpenOrCreate, FileAccess.Read);

byte[] MyData= new byte[fs.Length];
fs.Read(MyData, 0, System.Convert.ToInt32(fs.Length));

fs.Close();

da.Fill(ds,"MyImages");  // are they really filling a dataset with all those images???

DataRow myRow;
myRow=ds.Tables["MyImages"].NewRow();

myRow["Description"] = "This would be description text";
myRow["imgField"] = MyData;
ds.Tables["MyImages"].Rows.Add(myRow);
da.Update(ds, "MyImages");

con.Close();

Answer 1

You want the call to da.Fill() in order to get the schema for the MyImages table. That way you can use the DataRow returned by the call to NewRow() with the correct schema (columns, keys, etc) when assigning values to the columns.

You can tell the SqlDataAdapter to return only the schema with no data by setting the SqlDataAdapter.FillCommandBehavior:

da.FillCommandBehavior = CommandBehavior.SchemaOnly;
da.Fill(ds,"MyImages"); // Just get the schema for MyImages

DataRow myRow = ds.Tables["MyImages"].NewRow();
myRow["Description"] = "This would be description text";
myRow["imgField"] = MyData;
ds.Tables["MyImages"].Rows.Add(myRow);

da.Update(ds, "MyImages");

You can alternatively use da.FillSchema(), with either a single DataTable or a DataSet if your query returns multiple tables.

DataTable dt = new DataTable();

da.FillSchema(dt, SchemaType.Mapped);

DataRow myRow = dt.NewRow();
myRow["Description"] = "This would be description text";
myRow["imgField"] = MyData;
dt.Rows.Add(myRow);

da.Update(dt);