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

Database Application Programming(C#)

Chris North

CS 4604: DB

GUI/DB Application Model

Database

DataSet object

DB ConnectionDB AdapterDB 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: http://www.connectionstrings.com/

• 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