12. ADO.NET

1.Net programming ADO.NET NOEA / PQC 2009

12. ADO.NET

• Architecture• Connection factory• Config file• DataReader • DataSet• DataGrid• Autogeneration of SQL


Data access


Data Providers

• OLE DB:A COM object, that maps the OLE DB api to the DBMS' apiIs Microsoft propritary.

• ODBC: Works similar to a printer driver undependent of DBMS and OS

• .NET Data provider:A set of classes that implements a set of interfaces and abstract classes

• Some are provided by Microsoft and are installed with the .Net framework.

• Others are written by the DBMS provider


Microsoft Data Providers

• Data Provider Namespace Assembly• OLE DB System.Data.OleDb System.Data.dll• Microsoft SQL Server System.Data.SqlClient System.Data.dll• Microsoft SQL Server Mobile System.Data.SqlServerCe System.Data.SqlServerCe.dll• ODBC System.Data.Odbc System.Data.dll• Oracle System.Data.OracleClient System.Data.OracleClient.dll


Other providers

• Data Provider Website• Firebird Interbase http://www.mono-project.com/Firebird_Interbase• IBM DB2 Universal Database http://www-306.ibm.com/software/data/db2• MySQL http://dev.mysql.com/downloads/connector/net/1.0.html• PostgreSQL http://www.mono-project.com/PostgreSQL• Sybase http://www.mono-project.com/Sybase• Oracle (deres egen)

http://www.oracle.com/technology/tech/windows/odpnet/index.html


Classes and interfaces

• Object Base Class Implemented Interfaces• Connection DbConnection IDbConnection Forbindelse• Command DbCommand IDbCommand SQL kommando• DataReader DbDataReader IDataReader Forward reader• DataAdapter DbDataAdapter IDataAdapter Sammen med

Dataset• Parameter DbParameter IDataParameter Parametre i

kommando• Transaction DbTransaction IDbTransaction En transaktion


Overview of using databases

• 4 steps:

1. Open connection to database

2. Execute SQL for updating DB or fetching records

3. Handle data

4. Close connection


Step 1: Open Connection

• Connection are opened according to connection string info– here is a connection to a MS Access database opened– The database is located here: @"c:\AnyPlace\MyDb.mdb"– @ means that escape characters are discarded

using System.Data;

using System.Data.OleDb;

string sConnection;sConnection = "Provider=Microsoft.Jet.OLEDB.4.0;" + "Data Source="+@"c:\AnyPlace\MyDb.mdb");

OleDbConnection dbConn;dbConn = new OleDbConnection(sConnection);dbConn.Open();

connection


Step 2: Get / fetch data

• Data are fetched by creating a Command object and use it to execute a SQL statement.

• Data can be stored in either a DataReader object or a DataSet object.


Differences between DataReader and DataSet/DataAdapter

• DataReader can only be used for reading data.• It can only be traversed once (forward).

• DataAdapter is the connection between DataSet and database.• Data are fetched to the DataSet, might be modified and sent

back to the database.• Possible to traverse forward and backward.• A DataSet can contain multible tables.


Step 2: Get records Method 1: DataSet

• Get records by SQL Select query and DataAdapter– Data can be read and changed

string sql;sql = " Select lastname, firstname" + " From employee" + " Order By lastname Asc, firstname Asc;";

OleDbCommand dbCmd;dbCmd = new OleDbCommand(dbConn, sql);adapter.SelectCommand = dbCmd);dataset =new DataSet("MyTable");adapter.Fill(dataset); dataset

recordrecordrecord


Step 2: Get records Method 2: DataReader

• Get records via SQL Select query– read-only access to the database

string sql;sql = " Select lastname, firstname" + " From employee" + " Order By lastname Asc, firstname Asc;";

OleDbCommand dbCmd;dbCmd = new OleDbCommand(sql, dbConn);

OleDbDataReader dbReader;dbReader = dbCmd.ExecuteReader(); data reader

recordrecordrecord


What is achieved?

• We have created a connection to a database.

• The connection is placed in the connection object.

• We have done a search by using a SQL-statement.

• The search was executed by using a command object.

• The result of the search was stored in a DataSet or as here a DataReader object.

• Now it is possible to get the data from this object for viewing, passing on to client or handle in other ways.

• The following example shows how it can be done in a aspx file.


DataGrid• A simple example:

<%@ Page Language="C#" AutoEventWireup="true" %>

<%@ Import Namespace="System.Data" %><%@ Import Namespace="System.Data.OleDb" %>

Script kommer ind her.......

<html<head id="Head1" runat="server"> <title>Untitled Page</title></head><body> <form id="form1" runat="server"> <asp:DataGrid ID="MyDataGrid" runat="server"></asp:DataGrid> </form></body></html>


Datagrid (2)• The script by using DataReader:

<script runat="server"> OleDbDataReader data; protected void Page_Load(Object Src, EventArgs E) { String sConnection = "Provider=Microsoft.Jet.OLEDB.4.0;" + "Data Source=" + Server.MapPath("firma.mdb");

//Step 1: Open connection OleDbConnection dbConn = new OleDbConnection(sConnection); dbConn.Open();

//Step 2: Get data OleDbCommand dbCom = new OleDbCommand("select * from employee", dbConn); data = dbCom.ExecuteReader();

MyDataGrid.DataSource = data; MyDataGrid.DataBind(); }</script>


Datagrid (2)• The script by using DataSet:

<script runat="server"> OleDbDataReader data; protected void Page_Load(Object Src, EventArgs E) { String sConnection = "Provider=Microsoft.Jet.OLEDB.4.0;" + "Data Source=" + Server.MapPath("firma.mdb"); //Step 1: Open connection OleDbConnection dbConn = new OleDbConnection(sConnection); dbConn.Open(); //Step 2: Get data OleDbCommand dbCom = new OleDbCommand("select * from employee", dbConn);

OleDbDataAdapter adapter = new OleDbDataAdapter(); adapter.SelectCommand = dbCom; DataSet data = new DataSet(); adapter.Fill(data);

MyDataGrid.DataSource = data; MyDataGrid.DataBind(); }</script>


Factory

• Problem: Unlike ODBC, knowledge of the implementation might be spread to many places in the application.That's because of the set of dedicated classes

• The solution is to use a factory (from factory pattern)• In ADO.NET 2.0, it is implemented in the framework.

Otherwise you have to implement it yourself (see Troelsen).

• A coupIe of examples follows:

1. Which .Net providers are available

2. Use factory to create a Connection and a Command object


Which .NET data providers are installed?

• The information is collected from machine.config

using System.Data;using System.Data.Common;.....DataTable dt = DbProviderFactories.GetFactoryClasses();foreach (DataRow dr in dt.Rows){

Console.WriteLine("{0}\t\t{1}\t\t{2}", dr[0], dr[1],dr[2]);}

Odbc Data Provider .Net Framework Data Provider for Odbc System.Data.OdbcOleDb Data Provider .Net Framework Data Provider for OleDb System.Data.OleDbOracleClient Data Provider .Net Framework Data Provider for Oracle System.Data.OracleClientSqlClient Data Provider .Net Framework Data Provider for SqlServer System.Data.SqlClient


Use factory to create Connection and Command objects

• Here is no references in the source code to concrete classes• provider and connectionString may be placed in the config file

string provider = "System.Data.OleDb";string connectionString = "Provider=Microsoft.Jet.OLEDB.4.0; Data Source=firma.mdb";DbProviderFactory factory= DbProviderFactories.GetFactory(provider);DbConnection conn=factory.CreateConnection();conn.ConnectionString=connectionString;conn.Open();Console.WriteLine(conn.State);

DbCommand command = factory.CreateCommand();command.CommandText = "SELECT * FROM employee";command.Connection = conn;DbDataReader dataReader = command.ExecuteReader();while (dataReader.Read()){

Console.WriteLine(dataReader[1]);}


Connection strings

• Connection strings depends on the provider and are not well documented

• Where to get help?– www.connectionstrings.com– www.carlprothman.net/Default.aspx?tabid=81– Providers documentation

• Visual Studio can generate some of them


.Config fil• Configuration files are used several places in .Net• i.e in ASP.NET for setting site properties and security• In Remoting for setting remote object properties• In ADO.NET to set provider and connection string• You might also use own application dependent properties• In a .Net application the config file should be called

<full assemblyname.config>, i.e test.exe.config or test.dll.config

• If you call it app.config in Visual Studio, it automatically copied and renamed when the application is built.

• In ASP.NET it must be named web.config. You might define one in different sub folders, but the security part (authentification e.g.) must be in the root folder of the site.


.config fil and ADO.NET

• Example of SQLExpress connection string:

<?xml version="1.0" encoding="utf-8" ?><configuration> <configSections> </configSections> <connectionStrings> <add name="TestConnection" connectionString="Data Source=pcm06463\sqlexpress;Initial Catalog=dbtest; User ID=test;Password=" providerName="System.Data.SqlClient" /> </connectionStrings></configuration>

Machine name

Nessesary for sqlexpress

Database

Internal name


Get provider and connection string

• From ConfigurationManager:

.... string provider = ConfigurationManager.ConnectionStrings["TestConnection"].ProviderName; string connStr = ConfigurationManager.ConnectionStrings["TestConnection"].ConnectionString;.....


A (nearly) complete example in ASP.NET protected void Page_Load(object sender, EventArgs e) { if (!IsPostBack) { string provider = ConfigurationManager.ConnectionStrings["TestConnection"].ProviderName; string connStr = ConfigurationManager.ConnectionStrings["TestConnection"].ConnectionString; DbProviderFactory factory = DbProviderFactories.GetFactory(provider); DbConnection conn = factory.CreateConnection(); conn.ConnectionString = connStr; conn.Open(); DbCommand command = factory.CreateCommand(); command.CommandText = "SELECT * FROM datotest"; command.Connection = conn;

DataSet ds = new DataSet("TestDataSet"); DbDataAdapter da = factory.CreateDataAdapter(); da.SelectCommand = command; da.Fill(ds); MitGitter.DataSource = ds; MitGitter.DataBind(); } }


The Aspx file

<%@ Page Language="C#" AutoEventWireup="true" CodeFile="Default.aspx.cs" Inherits="_Default" %><!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">

<html xmlns="http://www.w3.org/1999/xhtml" ><body> <form id="form1" runat="server"> <div> <asp:GridView ID="MitGitter" runat="server"/> </div> </form></body></html>


Parameters in SQL statements• Makes it possible to use the same SQL-statement in multible

situations.• But harder to debug

string sqlString = "INSERT INTO datotest Values (@dato)"; SqlParameter sqlParam = new SqlParameter("@dato", System.Data.SqlDbType.DateTime); sqlParam.Value = DateTime.Now;

SqlCommand comm = _conn.CreateCommand(); comm.CommandText = sqlString; comm.Parameters.Add(sqlParam);

int result = comm.ExecuteNonQuery();ExecuteNonQuery is

used for insert, delete and update

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12. ADO.NET