Database Application Programming (C#) Chris North CS 4604: DB

GUI/DB Application Model Database DataSet object DB Connection DB Adapter DB SQL Query Win Form DataGrid control

Architecture Layers Database DB EngineDBMS UI DB Driver DB API Application Data Objects App UI SQLserver, Access Database SQLserver, Jet ODBC, OleDB, JDBC ADO, JDBC WinForms, Swing DB Admin App User OS Application Internet, local … … …

C# DataBase Access (ADO.net) OleDB, ODBC, SQLdb, … Steps to get data: 1.dbConnection: connect to DB 2.dbCommand: SQL query text 3.dbAdapter: executes query 4.DataSet: resulting data Steps to display data: Bind to UI control, e.g. DataGrid or Manual data processing DB Alternative: DataReader, retrieve data incrementally

C# DB Example Get data: Using System.Data.OleDb;// “Jet” = MS Access DB driver con = new OleDbConnection("Provider=Microsoft.Jet.OLEDB.4.0;Data Source=c:/mydb.mdb”); cmd = new OleDbCommand("SELECT * FROM mytable”, con); // SQL query adpt = new OleDbDataAdapter(cmd); data = new DataSet( ); adpt.Fill(data); // execute the query and put result in ‘data’ Display data: dataGrid1.DataSource = data.Tables[0];// show the table in the grid control MessageBox.Show(data.Tables[0].Rows[0][5].ToString( )); // or process manually, this is row 0 col 5

DataSet vs. DataReader DataSet: Like 2D array: a[r][c] Full dataset read from DB at query execution time Dataset cached locally in mem Can disconnect from DB Implemented using DataReader (Adapter) + random data access - Limited scalability - initial read very slow DataReader: (standard) 1 row at a time No local memory storage Fetch each row from DB on demand “cursor” = current row Must stay connected to DB + scalability - each row slow - random access difficult

Object Model DataSet: Tables[n] –Rows[r] columns[c] –Value, type, … –Columns info [c] Name, type, … DataReader: (standard) Columns[c] (current row) –Value, type, … Columns info [c] –Name, type, … Cursor: –moveNext, MovePrev, moveTo –EOF

Cursors Forward only vs. forward/back vs. random access Read only vs. writeable …

Connections Connection strings: Tons o examples: Con.open( ) Queries here Con.close( ) // connections consume resources Adapter.Fill( ) does open/close automatically

Commands (Queries) Command Types: SQL Query: »Relation: SELECT »Scalar: SELECT that returns 1 row, 1 col »Non-query: INSERT, UPDATE, DELETE Table name View name Rdr = Cmd.ExecuteReader( );

Query Parameters Want to substitute a parameter value into a query Dynamic SQL query construction: cmd = new OleDbCommand( "SELECT * FROM table WHERE myAttr = " + myValue, con); but: what if myValue contains weird chars? Parameterized query: (more robust, reusable) cmd = new OleDbCommand( "SELECT * FROM table WHERE myAttr = ?", con); // ? = parameter cmd.Parameters.Add(“?”, myValue); // parameter value Or, put param query in DB as view / stored procedure: cmd = new OleDbCommand("MyStoredQuery", con);// name of view cmd.CommandType = System.Data.CommandType.StoredProcedure; cmd.Parameters.Add("?", myValue);// parameter value

DataBound UI Controls Display a table: DataGrid Display a column: DataList listBox ComboBox Display a cell value: (of current row) TextBox Can bind any property of any UI control to any DB column DataGrid control -scroll, sort, edit, …

Manual data processing foreach(DataRow r in dataSet1.Tables[0].Rows) // for each row { doSomethingWith(r[“columnName”]); //or: foreach(Object v in r.ItemArray) // for each column doSomethingWith(v); }

Saving Data Changes Manual update/insert/delete queries: cmd = new OleDbCommand(“UPDATE table SET myAttr=value WHERE id=idval”, con); cmd.ExecuteNonQuery();// query does not return data. Adapters and bound UI Controls: User can edit in DataGrid, etc. Writes DataSet changes to DB on Update( ) method Must have param update/insert/delete commands in Adapter cmd = new OleDbCommand(" UPDATE table SET attr1=?, attr2=? WHERE id=?", con); cmd.Parameters.Add(new OleDbParameter(“?”, …, “attr1”, DataRowVersion.Current )); cmd.Parameters.Add(new OleDbParameter(“?”, …, “attr2”, DataRowVersion.Current )); cmd.Parameters.Add(new OleDbParameter(“?”, …, “id”, DataRowVersion.Original )); adpt.UpdateCommand = cmd; adpt.Update(data);// analogous to adpt.Fill(data);

Getting DB Schema Info Get list of tables in the DB: con.Open(); System.Data.DataTable t = con.GetOleDbSchemaTable( System.Data.OleDb.OleDbSchemaGuid.Tables, new object[]{null,null,null,"TABLE"} );

Visualization Draw graphics in Paint event Scale data coords to pixel coords E.g. scatterplot: foreach(DataRow r in dataSet1.Tables[0].Rows) // for each row { x = r[“attr1”] * Width / maxValue1; // Scale x,y to fit into window y = Height - r[“attr2”] * Height / maxValue2; // also flip y axis e.Graphics.FillEllipse(Brushes.Red, x, y, 10, 10); }

Interaction Mouse Events Scale mouse coords back into data coords Parameterized SQL query E.g. 2 clicks define a rectangle: Rect.left = click1.x / Width * maxValue1;// scale click x,y back to data range … SELECT * FROM table WHERE attr1 >= {rect.left} AND attr1 <= {rect.right} AND attr2 >= {rect.top} AND attr2 <= {rect.bottom} doSomething with results… Refresh( ); // repaint the window to show results in Paint event