PLATFORM TECHNOLOGY UNIT-4

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1 VB.NET: Handling Exceptions Delegates and Events - Accessing Data ADO.NET Object Model-.NET Data Providers Direct Access to Data Accessing Data with Datasets. ADO.NET Object Model ADO.NET object model provides an infrastructure that allows user access data from different Data Sources. ADO.NET provides a set of classes for working with data. ADO.NET is a set of classes, interfaces, structures and enumerations that manage data access in the.net framework ADO.NET has following attributes: 1. Consists of set of classes that user can use to connect to and manipulate data source 2. Transfer data into xml format between the database and your web application etc. There are two main component of this object model Dataset and Net data provider DATASET The dataset is a disconnected, in-memory representation of data. It can be considered as a local copy of the relevant portions of the database. The DataSet is persisted in memory and the data in it can be manipulated and updated independent of the database. When the use of this DataSet is finished, changes can be made back to the central database for updating. The data in DataSet can be loaded from any valid data source like Microsoft SQL server database, an Oracle database or from a Microsoft Access database. Dataset Datatable DataTable Odbc provider Sqlserver data provider Oledb.Netprovider Oracle Dataprovider Odbc sources Sqlserver Oledb sources Oracle sources DATA PROVIDERS RAJIV GANDHI COLLEGE OF ENGINEERING & TECHNOLOGY/CSE Page 1

2 ADO.NET Data Providers are class libraries that allow a common way to interact with specific data sources or protocols. The library APIs have prefixes that indicate which provider they support DATA PROVIDER The Data Provider is responsible for providing and maintaining the connection to the database. A DataProvider is a set of related components that work together to provide data in an efficient and performance driven manner. The.NET Framework currently comes with two DataProviders: the SQL Data Provider which is designed only to work with Microsoft's SQL Server 7.0 or later and the OleDb DataProvider which allows us to connect to other types of databases like Access and Oracle. Each DataProvider consists of the following component classes: Connection object Command object DataReader object DataAdapter object Component classes that make up the Data Providers The Connection Object The Connection object creates the connection to the database. Microsoft Visual Studio.NET provides two types of Connection classes: the SqlConnection object, which is designed specifically to connect to Microsoft SQL Server 7.0 or later, and RAJIV GANDHI COLLEGE OF ENGINEERING & TECHNOLOGY/CSE Page 2

3 the OleDbConnection object, which can provide connections to a wide range of database types like Microsoft Access and Oracle. The Connection object contains all of the information required to open a connection to the database. The Command Object The Command object is represented by two corresponding classes: SqlCommand and OleDbCommand. Command objects are used to execute commands to a database across a data connection. The Command objects can be used to execute stored procedures on the database, SQL commands, or return complete tables directly. Command objects provide three methods that are used to executecommands on the database: ExecuteNonQuery: Executes commands that have no return values such as INSERT, UPDATE or DELETE ExecuteScalar: Returns a single value from a database query Executereader: Returns a result set by way of a DataReader object The DataReader Object The DataReader object provides a forward-only, read-only, connected stream recordset from a database. Unlike other components of the Data Provider, DataReader objects cannot be directly instantiated. DataReader is returned as the result of the Command object's ExecuteReader method. The SqlCommand.ExecuteReader method returns a SqlDataReader object, and the OleDbCommand.ExecuteReader method returns an OleDbDataReader object. The DataReader can provide rows of data directly toapplication logic when you do not need to keep the data cached in memory. Because only one row is in memory at a time, the DataReader provides the lowest overhead in terms of system performance but requires the exclusive use of an open Connection object for the lifetime of the DataReader. The DataAdapter Object The DataAdapter is the class at the core of ADO.NET's disconnected data access. It is essentially the middleman facilitating all communication between the database and a DataSet. RAJIV GANDHI COLLEGE OF ENGINEERING & TECHNOLOGY/CSE Page 3

4 The DataAdapter is used either to fill a DataTable or DataSet with data from the database with its Fill method. After the memory-resident data has been manipulated, the DataAdapter can commit the changes to the database by calling the Update method. The DataAdapter provides four properties that represent database commands: SelectCommand InsertCommand DeleteCommand UpdateCommand When the Update method is called, changes in the DataSet are copied back to the database and the appropriate InsertCommand, DeleteCommand, or UpdateCommand is executed..net DATA PROVIDERS.NET DATA PROVIDERS 1. Microsoft SQL Server.NET Data Provider (System.Data.SqlClient) The Microsoft SQL Server.NET Data Provide allows you to connect to a Microsoft SQL Server 7.0, 2000, and 2005 databases. 2. ODBC.NET Data Provider (System.Data.ODBC) 3. OLE DB.NET Data Provider (System.Data.OleDb).NET DATA PROVIDERS OBJECTS The Connection object which provides a connection to the database The Command object which is used to execute a command The DataReader object which provides a forward-only, read only, connected recordset The DataAdapter object which populates a disconnected DataSet with data and performs update DataColumn object This is the building block of the DataTable. A number of such objects make up a table. Each DataColumn object has a DataType property that determines the kind of data that the column is holding. A control can be bound simply such as a TextBox to a column within a data table RAJIV GANDHI COLLEGE OF ENGINEERING & TECHNOLOGY/CSE Page 4

5 Data Table A DataTable object is the representation of a table, with rows and columns, in ADO.NET. A DataTable can be considered to a collection of two kinds viz., DataColumn objects and DataRows object. You can complex-bind a control to the information contained in a data table. Controls like DataGrid are used for this purpose DataView object A DataView object is a customized view of a single data table that may be filtered or sorted. A data view is the data snapshot used by complex-bound controls. You can simple-bind or complex-bind to the data within the DataView. This is not an updating data source.dataset object A DataSet is a collection of tables, relationships and constraints. You can simple-bind or complex bind to the data within the dataset..dataviewmanager Object A DataViewManager object is a customized view of the whole DataSet. It is an extended form of a DataView with realations included and with multiple tables. For MS SQL server we have corresponding Connection, Command, datareader and data adapter object They are: SqlDataReader SqlDataAdapter RAJIV GANDHI COLLEGE OF ENGINEERING & TECHNOLOGY/CSE Page 5

6 SqlConnection SqlCommand Connection string SqlConnection osqlconn = new SqlConnection(); osqlconn.connectionstring = "Data Source=(local);" + "Initial Catalog=myDatabaseName;" + "Integrated Security=SSPI"; For My SQL we have corresponding Connection, Command, datareader and data adapter object They are: OdbcDataReader OdbcDataAdapter OdbcConnection OdbcCommand Connection string Dim sconnstring As String = "Driver=SQL Server;" & "Server=MySQLServerName;" & _ "Database=MyDatabaseName;" & "Uid=MyUsername;" & "Pwd=MyPassword" For Oracle server we have corresponding Connection, Command, datareader and data adapter object They are: OracleDataReader OracleDataAdapter OracleConnection OracleCommand For MS Access/ Excel we have corresponding Connection, Command, datareader and data adapter object They are: OledbDataReader OledbDataAdapter OledbConnection OledbCommand Connection string con.connectionstring = "Provider=Microsoft.Jet.OLEDB.4.0;DataSource=D:\\employee.mdb"; RAJIV GANDHI COLLEGE OF ENGINEERING & TECHNOLOGY/CSE Page 6

7 Accessing Data with Datasets ADO.NET DataSets The DataSet object is central to supporting disconnected, distributed data scenarios with ADO.NET. The DataSet is a memory-resident representation of data that provides a consistent relational programming model regardless of the data source. It can be used with multiple and differing data sources, with XML data, or to manage data local to the application. The DataSet represents a complete set of data, including related tables, constraints, and relationships among the tables. The connection to the database has been made. The next step is to pull the records from the table. To do that, a Dataset and a DataAdapter are needed. The DataAdapter will fill the Dataset with records from the database. Generally DataSet has two types which are namely as follows: Typed DataSet: Those Dataset which applies the information contained in the XSD to create a typed class, this DataSet is said to be a Typed Dataset. Typed DataSet are basically used to raed data from XML file. Untyped DataSet: Untyped DataSet does not have any schema. It is exposed simply as a mere collection. The following illustration shows the DataSet object model. RAJIV GANDHI COLLEGE OF ENGINEERING & TECHNOLOGY/CSE Page 7

8 The methods and objects in a DataSet are consistent with those in the relational database model. The DataTableCollection An ADO.NET DataSet contains a collection of zero or more tables represented by DataTable objects. The DataTableCollection contains all the DataTable objects in a DataSet. A DataTable is defined in the System.Data namespace and represents a single table of memory-resident data. It contains a collection of columns represented by a DataColumnCollection, and constraints represented by a ConstraintCollection, which together define the schema of the table. A DataTable also contains a collection of rows represented by the DataRowCollection, which contains the data in the table. Along with its current state, a DataRow retains both its current and original versions to identify changes to the values stored in the row. The DataView Class RAJIV GANDHI COLLEGE OF ENGINEERING & TECHNOLOGY/CSE Page 8

9 A DataView enables you to create different views of the data stored in a DataTable, a capability that is often used in data-binding applications. Using a DataView, you can expose the data in a table with different sort orders, and you can filter the data by row state or based on a filter expression. The DataRelationCollection A DataSet contains relationships in its DataRelationCollection object. A relationship, represented by the DataRelation object, associates rows in one DataTable with rows in another DataTable. A relationship is analogous to a join path that might exist between primary and foreign key columns in a relational database. A DataRelation identifies matching columns in two tables of a DataSet. Relationships enable navigation from one table to another in a DataSet. The essential elements of a DataRelation are the name of the relationship, the name of the tables being related, and the related columns in each table. Relationships can be built with more than one column per table by specifying an array of DataColumn objects as the key columns. When you add a relationship to the DataRelationCollection, you can optionally add a UniqueKeyConstraint and a ForeignKeyConstraint to enforce integrity constraints when changes are made to related column values. To create a Dataset object, add the following just above the form load event: DataSet ds1; Inside of the form load event, create a new object from the Dataset type we've called ds1: ds1 = new DataSet(); Add the code just after your con.open line. For the DataAdapter, add the following outside of the form load event: System.Data.SqlServerCe.SqlCeDataAdapter da; We're setting up a DataAdapter variable, here, and calling it da. Inside of the form load event, we can create a new object from our da variable. Add these two lines just after your ds1 line: RAJIV GANDHI COLLEGE OF ENGINEERING & TECHNOLOGY/CSE Page 9

10 String sql = "SELECT * From tbl_employees"; da = new System.Data.SqlClient.SqlDataAdapter( sql, con ); The first line sets up a string variable called sql. SQL stands for Structured Query Language. It's a language used to pull records from a database, and variants of it are used for all database systems. ACCESSING DATA WITH DATASETS Coding using System; using System.Collections.Generic; using System.ComponentModel; using System.Data; using System.Data.SqlClient; using System.Drawing; using System.Linq; using System.Text; using System.Windows.Forms; namespace UpdatingData public partial class Form1 : Form public Form1() InitializeComponent(); private void Form1_Load(object sender, EventArgs e) SqlConnection conn = new Source=yourServerName;user id=username;password=password;" + "Initial Catalog=DatabaseName"); SqlDataAdapter thisadapter = new SqlDataAdapter( "SELECT EMPNO,ENAME FROM EMP", conn); SqlCommandBuilder thisbuilder = new SqlCommandBuilder(thisAdapter); RAJIV GANDHI COLLEGE OF ENGINEERING & TECHNOLOGY/CSE Page 10

11 DataSet ds = new DataSet(); thisadapter.fill(ds, "Employee"); Console.WriteLine("name before change: 0", ds.tables["employee"].rows[5]["ename"]); ds.tables["employee"].rows[5]["ename"] = "Johnson"; thisadapter.update(ds, "Employee"); Console.WriteLine("name after change: 0", ds.tables["employee"].rows[5]["ename"]); Here, SqlConnection conn = new Source=yourServerName;user id=username;password=password;" + "Initial Catalog=DatabaseName"); The above block of code is SQL Server specific connection String to the database SqlDataAdapter thisadapter = new SqlDataAdapter( "SELECT EMPNO,ENAME FROM EMP", conn); Here we create a DataAdapter object to Operations such as Update SqlCommandBuilder thisbuilder = new SqlCommandBuilder(thisAdapter); The SqlCommandBuilder is used to build SQL statements DataSet ds = new DataSet(); Here, we create a DataSet object to hold data. thisadapter.fill(ds, "Employee"); In the above statement we will the DataSet with the query we have previously defined for the DataAdapter. RAJIV GANDHI COLLEGE OF ENGINEERING & TECHNOLOGY/CSE Page 11

12 Console.WriteLine("Name before change: 0",ds.Tables["Employee"].Rows[5]["ENAME"]); Displaying the data before change ds.tables["employee"].rows[5]["ename"] = "Johnson"; In the above line, we change the data in Employee table, row 5 with the column name ENAME thisadapter.update(ds, "Employee"); Here we make a call to the Update command to make the changes permanent to the database Table. Console.WriteLine("Name after change: 0",ds.Tables["Employee"].Rows[5]["ENAME"]); HOW TO ACCESING DATA WITH ADO.NET HOW TO ACCESING DATA WITH ADO.NET Client makes request Create a sqldatasource Return the data to the client Update the data Use the SQLdatasource to open a data base connection, update the database and close the connection The connection to the database has been made. The next step is to pull the records from our Employees table. To do that, a Dataset and a DataAdapter are needed. A Dataset is where all your data is held when it is pulled from the database table. Think of it like a grid that you see on a spreadsheet. The Columns in the grid are the Columns from your database table. The Rows represent a single entry in the table. The Dataset needs to be filled with data. However, because the Dataset and Connection object can't see each other, they need someone in the middle to help them out - the DataAdapter. The DataAdapter will fill the Dataset with records from the database. RAJIV GANDHI COLLEGE OF ENGINEERING & TECHNOLOGY/CSE Page 12

13 Access data using ADO.NET and make changes to it. Program. Listing 1. SqlConnection Demo using System; using System.Data; using System.Data.SqlClient; /// <summary> /// Demonstrates how to work with SqlCommand objects /// </summary> class SqlCommandDemo SqlConnection conn; public SqlCommandDemo() // Instantiate the connection conn = new SqlConnection( "Data Source=(local);Initial Catalog=Northwind;Integrated Security=SSPI"); // call methods that demo SqlCommand capabilities static void Main() SqlCommandDemo scd = new SqlCommandDemo(); Console.WriteLine(); Console.WriteLine("Categories Before Insert"); Console.WriteLine(" "); // use ExecuteReader method scd.readdata(); // use ExecuteNonQuery method for Insert scd.insertdata(); Console.WriteLine(); Console.WriteLine("Categories After Insert"); Console.WriteLine(" "); scd.readdata(); // use ExecuteNonQuery method for Update scd.updatedata(); Console.WriteLine(); Console.WriteLine("Categories After Update"); Console.WriteLine(" "); scd.readdata(); // use ExecuteNonQuery method for Delete scd.deletedata(); Console.WriteLine(); RAJIV GANDHI COLLEGE OF ENGINEERING & TECHNOLOGY/CSE Page 13

14 Console.WriteLine("Categories After Delete"); Console.WriteLine(" "); scd.readdata(); // use ExecuteScalar method int numberofrecords = scd.getnumberofrecords(); Console.WriteLine(); Console.WriteLine("Number of Records: 0", numberofrecords); /// <summary> /// use ExecuteReader method /// </summary> public void ReadData() SqlDataReader rdr = null; try // Open the connection conn.open(); // 1. Instantiate a new command with a query and connection SqlCommand cmd = new SqlCommand("select CategoryName from Categories", conn); // 2. Call Execute reader to get query results rdr = cmd.executereader(); // print the CategoryName of each record while (rdr.read()) Console.WriteLine(rdr[0]); finally // close the reader if (rdr!= null) rdr.close(); // Close the connection if (conn!= null) conn.close(); RAJIV GANDHI COLLEGE OF ENGINEERING & TECHNOLOGY/CSE Page 14

15 /// <summary> /// use ExecuteNonQuery method for Insert /// </summary> public void Insertdata() try // Open the connection conn.open(); // prepare command string string insertstring into Categories (CategoryName, Description)values 'Miscellaneous', 'Whatever doesn''t fit elsewhere')"; // 1. Instantiate a new command with a query and connection SqlCommand cmd = new SqlCommand(insertString, conn); // 2. Call ExecuteNonQuery to send command cmd.executenonquery(); finally // Close the connection if (conn!= null) conn.close(); /// <summary> /// use ExecuteNonQuery method for Update /// </summary> public void UpdateData() try // Open the connection conn.open(); // prepare command string string updatestring Categories set CategoryName = 'Other' where CategoryName = 'Miscellaneous'"; RAJIV GANDHI COLLEGE OF ENGINEERING & TECHNOLOGY/CSE Page 15

16 // 1. Instantiate a new command with command text only SqlCommand cmd = new SqlCommand(updateString); // 2. Set the Connection property cmd.connection = conn; // 3. Call ExecuteNonQuery to send command cmd.executenonquery(); finally // Close the connection if (conn!= null) conn.close(); /// <summary> /// use ExecuteNonQuery method for Delete /// </summary> public void DeleteData() try // Open the connection conn.open(); // prepare command string string deletestring from Categories where CategoryName = 'Other'"; // 1. Instantiate a new command SqlCommand cmd = new SqlCommand(); // 2. Set the CommandText property cmd.commandtext = deletestring; // 3. Set the Connection property cmd.connection = conn; // 4. Call ExecuteNonQuery to send command cmd.executenonquery(); RAJIV GANDHI COLLEGE OF ENGINEERING & TECHNOLOGY/CSE Page 16

17 finally // Close the connection if (conn!= null) conn.close(); /// <summary> /// use ExecuteScalar method /// </summary> /// <returns>number of records</returns> public int GetNumberOfRecords() int count = -1; try // Open the connection conn.open(); // 1. Instantiate a new command SqlCommand cmd = new SqlCommand("select count(*) from Categories", conn); // 2. Call ExecuteScalar to send command count = (int)cmd.executescalar(); finally // Close the connection if (conn!= null) conn.close(); return count; (OR) ACCESSING DATA USING ODBC CONNECTIVITY RAJIV GANDHI COLLEGE OF ENGINEERING & TECHNOLOGY/CSE Page 17

18 FORM DESIGN SOURCE CODE using System; using System.Collections.Generic; using System.ComponentModel; using System.Data; using System.Drawing; using System.Linq; using System.Text; using System.Windows.Forms; using System.Data.Odbc; namespace DBCSHARP RAJIV GANDHI COLLEGE OF ENGINEERING & TECHNOLOGY/CSE Page 18

19 public partial class Form1 : Form OdbcConnection con; OdbcCommand com; OdbcDataReader rp; public Form1() InitializeComponent(); private void Form1_Load(object sender, EventArgs e) con = new OdbcConnection(); com = new OdbcCommand(); con.connectionstring = "Driver=Microsoft ODBC for Oracle;Server=localhost;Uid=system;Pwd=cse;"; con.open(); com.connection = con; private void button1_click(object sender, EventArgs e) if ((String.IsNullOrEmpty(this.t_reg.Text)) (string.isnullorempty(this.t_name.text)) (string.isnullorempty(this.t_dept.text)) (string.isnullorempty(this.t_add.text))) MessageBox.Show("please fill all the details"); com.commandtext = "insert into table2 values(" + this.t_reg.text + ",'" + this.t_name.text + "','" + this.t_dept.text + "','" + this.t_add.text + "')"; com.executenonquery(); MessageBox.Show("Record Inserted"); RAJIV GANDHI COLLEGE OF ENGINEERING & TECHNOLOGY/CSE Page 19

20 private void button2_click(object sender, EventArgs e) com.commandtext = "update table2 set name='" + t_name.text + "',dept='" + t_dept.text + "',address='" + t_add.text + "' where regno =" + combo.selecteditem + ""; com.executenonquery(); MessageBox.Show("Record Updated"); this.t_reg.clear(); this.t_name.clear(); this.t_dept.clear(); this.t_add.clear(); private void button3_click(object sender, EventArgs e) com.commandtext = "delete from table2 where regno=" + this.combo.selecteditem + ""; com.executenonquery(); this.combo.items.remove(combo.selecteditem); this.t_reg.clear(); this.t_name.clear(); this.t_dept.clear(); this.t_add.clear(); MessageBox.Show("Record Deleted"); private void combobox1_selectedindexchanged(object sender, EventArgs e) com.commandtext = "select*from table2 where regno=" + combo.selecteditem + ""; rp = com.executereader(); if (rp.read()) this.t_name.text = rp.getstring(1); this.t_dept.text = rp.getstring(2); RAJIV GANDHI COLLEGE OF ENGINEERING & TECHNOLOGY/CSE Page 20

21 this.t_add.text = rp.getstring(3); rp.close(); private void radiobutton2_checkedchanged(object sender, EventArgs e) this.t_reg.hide(); this.combo.items.clear(); this.button1.enabled = false; this.combo.visible = true; this.button2.enabled = true; this.button3.enabled = true; com.commandtext = "select* from table2"; rp = com.executereader(); while (rp.read()) this.combo.items.add(rp.getvalue(0)); rp.close(); private void radiobutton1_checkedchanged(object sender, EventArgs e) this.t_reg.show(); this.t_reg.clear(); this.t_name.clear(); this.t_dept.clear(); this.t_add.clear(); this.combo.visible = false; this.button1.enabled = true; this.button2.enabled = false; this.button3.enabled = false; RAJIV GANDHI COLLEGE OF ENGINEERING & TECHNOLOGY/CSE Page 21

22 DATABASE DESIGN REGNO NAME DEPT ADDRESS 1 AA CSE 12,WDFWF 2 BB ECE 13,SGFRGY 3 CC EEE 14,FGFS 4 DD MECH 16,DRGEY RAJIV GANDHI COLLEGE OF ENGINEERING & TECHNOLOGY/CSE Page 22

23 RAJIV GANDHI COLLEGE OF ENGINEERING & TECHNOLOGY/CSE Page 23

UNIT III APPLICATION DEVELOPMENT ON.NET

UNIT III APPLICATION DEVELOPMENT ON.NET Syllabus: Building Windows Applications, Accessing Data with ADO.NET. Creating Skeleton of the Application Select New->Project->Visual C# Projects->Windows Application