Introduction to ADO.NET Programming. ADO.NET Objects Data Set.NET Applications Data Reader Command...

Introduction to ADO.NET Programming

ADO.NET Objects

Data Set

.NET Applications

Data Reader

Command Object

Connection Object

Managed Data Provider(OLEDB)

Database

Adapter

Connection with a Connection Object

• A connection object represents a unique session with a data source.

• Connection string: database, OLE DB provider, password, if any, security, etc.

• Use the Open/Close method to open/close a connection.

• Other functions: – Manage transaction: BeginTransaction(), Commit,

rollBack.

Connection String

• Containing information about database, OLE DB provider, password, if any, security, etc.

• For Jet database:– ="Provider=Microsoft.Jet.OLEDB.4.0;Data Source = c:\sales2k.mdb"

Data Link Properties (Under the Advanced Tab of the Connection Dialog Window)

• Access permissions – Read—Read only.– ReadWrite—Read and write.– Share Deny None—Neither read nor write access can

be denied to others.– Share Deny Read—Prevents others from opening in

read mode.– Share Deny Write—Prevents others from opening in

write mode.– Share Exclusive—Prevents others from opening in

read/write mode. – Write—Write only.

Providers

• MSDASQL – Microsoft OLE DB Provider for ODBC

• Microsoft.Jet.OLEDB.3.51

• Microsoft.Jet.OLEDB.4.0

• MSDAORA – For Oracle

• SQLOLEDB – Microsoft SQL Server

Connection Object

• Example:– dim strConn as string ="Provider=Microsoft.Jet.OLEDB.4.0;Data Source = c:\

sales2k.mdb"

– dim objConn as new OledbConnection(strConn)

– objConn.open()

• Basic Methods:– Open, Close

– BeginTransaction

Command Object• The command object allows us to execute a SQL

statement.• Properties:

– CommandType: SQL or stored procedure– CommandText: SQL statement– Connection– Other properties:

• Parameters

• Basic Methods:– ExecuteReader: Creates a DataReader object that contains

the results of the query.– ExecuteNonQuery: Change the data in a database without

using a DataSet by executing SQL’s UPDATE, INSERT, or DELETE statements.

ExecuteReader Example

dim strConn as string ="Provider=Microsoft.Jet.OLEDB.4.0;Data Source = c:\sales2k.mdb"

dim objConn as new OledbConnection(strConn)

dim strSQL as string = "select * from customer;"

dim objComm as new OledbCommand(strSQL,objConn)

dim Results as string

objConn.open()

dim objDataReader as oledbDataReader

objDataReader=objComm.executeReader()

Import NameSpace

• The Imports statement must appear before all other declarations in a file and cannot appear inside a class or module declaration.– Imports System.Data.OleDb– Public Class Form1

DataReader Object

• It is read-only and forward-only cursor.

• Basic Methods:– Read: Reads the current record and advances

the pointer to the next record. It returns False if no more record in the DataReader.

– Close: Closes the dataReader.

Read Records in a DataReader

• dim Results as string• do while objDataReader.Read()=true

Results+=objDataReader("cid") + “ “ + objDataReader("Cname") + vbCrLF

• loop• Textbox1.text=Results

• Note: objDataReader.Item(0)• Note: objDataReader.Item(“cid”)

Add Items from a DataReader to a Listbox

Dim strConn As String = "Provider=Microsoft.Jet.OLEDB.4.0;Data Source = c:\sales2k.mdb"

Dim objConn As New OleDbConnection(strConn)

Dim strSQL As String = "select cname from customer;"

Dim objComm As New OleDbCommand(strSQL, objConn)

objConn.Open()

Dim objDataReader As OleDbDataReader

objDataReader = objComm.ExecuteReader()

Do While objDataReader.Read() = True

LISTBOX1.Items.Add(objDataReader("cname"))

Loop

Note1: Listbox is not bound. 2. SelectedItem

Note2: With the data binding you cannot issue the Add method.

Use a DataReader to Retrieve SummariesDim sfCount, laCount, aCount, bCount, cCOunt As Integer objConn.Open() Dim objDataReader As OleDbDataReader objDataReader = objComm.ExecuteReader() Do While objDataReader.Read() = True If objDataReader("city") = "sf" Then sfCount += 1 ElseIf objDataReader("city") = "la" Then laCount += 1 End If If objDataReader("rating") = "a" Then aCount += 1 ElseIf objDataReader("rating") = "b" Then bCount += 1 Else cCOunt += 1 End If Loop TextBox1.Text = sfCount.ToString TextBox2.Text = laCount.ToString TextBox3.Text = aCount.ToString TextBox4.Text = bCount.ToString TextBox5.Text = cCOunt.ToString

Use SQL to Retrieve Summaries



Dim strSQL As String = "select count(cid) as custCount from customer;"


Dim Results As String

objConn.Open()



If objDataReader.Read = True Then

MessageBox.Show(objDataReader("custCount").ToString)

End If

Testing for Null

If objDataReader.Read = True Then

If IsDBNull(objDataReader("custCount")) Then

TextBox1.Text = 0

Else

TextBox1.Text = objDataReader("custCount").ToString

End If

End If

To Reuse a DataReader

• objDataReader.Close()• objDataReader = objComm.ExecuteReader()

Error HandlingTry

objConn.Open()




Results += objDataReader("cid") + " " + objDataReader("Cname") + vbCrLf

Loop

TextBox1.Text = Results

objConn.Close()

Catch except As System.Exception

MessageBox.Show(except.Message)

End Try

Possible Database Errors

• SQL syntax errors

• Database connection not open

• Violate database constraints• Referential integrity

• Field data type and length

• Primary key constraint

ExecuteNonQuery Example

dim strSQLUpd as string="Update customer set rating = ‘A’”

strSQLUpd=strSQLUpd & " where cname='" & CnameList.selectedItem.text & "'“Dim objCommUpd As New OleDbCommand(strSQLUpd, objConn)

objCommUpd.ExecuteNonQuery()

Note: How many records affected by this command?

Messagebox.Show(objCommUpd.ExecuteNonQuery())

Demo

• Create a project that do the following tasks:– Use a DataReader to retrieve customer IDs and

populate a listbox.– Select a new rating from radio buttons for the

selected customer.– Update customer’s rating using the

ExecuteNonQuery method of a Command object.

Declare OleDB objects and create listboxImports System.Data.OleDb

Public Class Form3

Inherits System.Windows.Forms.Form



Dim strSQL As String = "select cid from customer;"


Private Sub Form3_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load

objConn.Open()




ListBox1.Items.Add(objDataReader("cid"))

Loop

objConn.Close()

End Sub

Update customer ratingPrivate Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click

objConn.Open()

Dim newRating As String

If RadioButton1.Checked = True Then

newRating = "A"

ElseIf RadioButton2.Checked Then

newRating = "B"

Else

newRating = "C"

End If

Dim strSQLUpd As String = "Update customer set rating = '" & newRating & "'"

strSQLUpd = strSQLUpd & " where cid='" & ListBox1.SelectedItem & "'"

Dim objCommUpd As New OleDbCommand(strSQLUpd, objConn)

objCommUpd.ExecuteNonQuery()

objConn.Close()

End Sub

Use Command Object’s ExecuteNonQuery to Insert A New Record

1. Create unbound text boxes to enter new record.

2. Add an Insert button with the following handler

Dim strSQLInsert As String

strSQLInsert = "Insert into Customer values ('"

strSQLInsert = strSQLInsert & TextBox1.Text & "','" & TextBox2.Text & "','"

strSQLInsert = strSQLInsert & TextBox3.Text & "','" & TextBox4.Text & "')"

Dim objCommInsert As New OleDbCommand(strSQLInsert, objConn)

objCommInsert.ExecuteNonQuery()

DataSet Object

• A DataSet object can hold several tables and relationships between tables.

• A DataSet is a set of disconnedted data. Data is extracted from the database and stored in the DataSet object. Updates to the DataSet must copy back to the database to make the changes permanent.

DataSet and Related Objects• DataSet: Can contain multiple tables and

relationships.• DataTable object: Represents a table in the

dataset.• DataAdapter: This the object used to pass data

between the database and the dataset. The Fill method copies the data into the dataset, and the Update method copies the updates back into the database.

• DataView: This represents a specific view of the DataTables held in the dataset.

DataSet and Related Objects

DataView

DataSetDataTable

DataTable

DataAdapter

Connection

Command

Structure of a Dataset

Dataset

Tables

Data table

Rows

Data Row

Columns

Data Column

Constraints

ConstraintRelations

Data Relation

Reading Data into a Table

• dim strConn as string ="Provider=Microsoft.Jet.OLEDB.4.0;Data Source = c:\sales2k.mdb"

• dim objConn as new OledbConnection(strConn)

• dim strSQL as string = "select * from customer;"

• dim objDataSet as new Dataset()

• dim objAdapter as new OledbDataAdapter(strSQL, objConn)

• objAdapter.Fill(objDataSet, "Cust")

Binding a Table in a Dataset to a DataGridImports System.Data.OleDb

Public Class Form4




Dim objDataSet As New DataSet()


Dim strSQL As String = "select * from customer;"

Dim objAdapter As New OleDbDataAdapter(strSQL, objConn)

objAdapter.Fill(objDataSet, "Cust")

DataGrid1.DataSource = objDataSet

DataGrid1.DataMember = "Cust"

End Sub

Note: Adapter’s Fill method is able to open the connection.

DataView ObjectA Better Way for Binding

• The DataView object exposes a complete table or a subset of the records from a table.

• Table’s DefaultView property:– Dim ObjDataView As New DataView()– ObjDataView.Table = objDataSet.Tables("Cust")– Or: ObjDataView = objDataSet.Tables("Cust").DefaultView

• DataView can be used as a DataSource in data binding.

Data Binding with DataView Object






objAdapter.Fill(objDataSet, "Cust")

Dim ObjDataView As New DataView()

ObjDataView = objDataSet.Tables("Cust").DefaultView

DataGrid1.DataSource = ObjDataView

Selecting a Subset of Records with DataView’s RowFilter Property

• objDataView.RowFilter = criteria

• Note: The criteria can be a simple or complex condition.

DataView ExampleDim ObjDataView As New DataView()

Dim newRating As String


newRating = "A"

ElseIf RadioButton2.Checked Then

newRating = "B"

Else

newRating = "C"

End If

ObjDataView.Table = objDataSet.Tables("Cust")

ObjDataView.RowFilter = "rating='" & newRating & "'"

DataGrid1.Visible = True


Accessing Records in DataView

Using DataView and DataRowView object’s Item property:

objdataView = objDataSet.Tables("customer").DefaultView

TextBox1.Text = objdataView.Item(rowIndex).Item(0)


Move to the next record:

rowIndex += 1



Note: To avoid out-of-bound, use the DataView’s Count property.

Defining an Adapter without A Command Object

• dim strConn as string ="Provider=Microsoft.Jet.OLEDB.4.0;Data Source = c:\sales2k.mdb"

• dim objConn as new OledbConnection(strConn)• dim strSQL as string = "select * from

customer;"• dim objDataSet as new Dataset()• dim objAdapter as new OledbDataAdapter(strSQL,

objConn)• objAdapter.Fill(objDataSet, "Cust")

Defining an Adapter with A Command Object

• dim strSQLCust as string = "select * from customer;"

• dim objComm as new OledbCommand()

• dim objAdapter as new OledbDataAdapter()

• dim objDataSet as new Dataset()

• objComm.Connection=objConn

• objComm.CommandType=COmmandType.Text

• objComm.CommandText=strSQLCust

• objAdapter.SelectCommand=objComm

• objConn.open()

• objAdapter.Fill(objDataSet, "Customer")

• Note:Adapter has SelectCommand, InsertCommand, DeleteCommand, UpdateCommand properties (Check Object Browser).

Creating Multiple Tables in A DataSet with One Adapter

• dim strSQLCust as string = "select * from customer;"

• dim strSQLOrder as string ="select * from orders;"

• dim objComm as new OledbCommand()• dim objAdapter as new OledbDataAdapter()• dim objDataSet as new Dataset()• objComm.Connection=objConn• objComm.CommandType=COmmandType.Text• objComm.CommandText=strSQLCust• objAdapter.SelectCommand=objComm• objConn.open()• objAdapter.Fill(objDataSet, "Customer")• objComm.COmmandText=strSQLOrder• objAdapter.Fill(objDataSet, "Orders")

Binding Multiple Tables to a DataGrid (Example 1)

DataGrid1.DataSource = objDataSet

Binding Multiple Tables to a DataGrid (Example 2)

Dim ObjDataView As New DataView()

Dim TableName As String


ObjDataView = objDataSet.Tables("Customer").DefaultView

Else

ObjDataView = objDataSet.Tables("Orders").DefaultView

End If


Adding Relationship to a Dataset

• The Dataset object has a Relations property. It is a collection of DataRelations. We can use a relationship to enforce the referential integrity.

• To define a DataRelation:– DataRelObj=DataRelation(RelationName, ParentTable

Field, ChildTableField)• Dim objRel As DataRelation

• objRel = New DataRelation("custOrder", objDataset.tables("customer").columns("cid"), objDataset.tables("orders").columns("cid"))

• Adding a relation to the dataset:– objDataSet.Relations.Add(objRel)

Creating a Hierarchical DataGrid

Dim objRel As DataRelation

objRel = New DataRelation("custOrder", objDataSet.Tables("customer").Columns("cid"), objDataSet.Tables("orders").Columns("cid"))

objDataSet.Relations.Add(objRel)

DataGrid1.DataSource = objDataSet.Tables("customer")

DataTable’s Rows Property

• This is a collection of all the records in a table, a collection of DataRow objects.

• DataRow object’s properties and methods.

Accessing a Record with Index

objAdapter.Fill(objDataSet, "Customer")

TextBox1.Text = objDataSet.Tables("Customer").Rows(rowIndex).Item(0)

TextBox2.Text = objDataSet.Tables("Customer").Rows(rowIndex).Item(1)

Access Rows in a DataRow Collection

• dim objTable as DataTable = objDataset.Tables("Customer")

• dim objRow as DataRow• For each objRow in objTable.Rows• strResult=strResult+“ " & objRow("cid") &

" " & objRow("cname") & vbCrLf

• Next

DataRow object’s GetChildRows Method

• Returns a collection of rows from another table that are related as child rows to this row.

Displaying Parent/Child Records in a Relation

• Define the relation.

• Specify the relation in the GetChildRows method of the DataRow object.

Imports System.Data.OleDb

Public Class Form1



Dim objConn As New OledbConnection(strConn)

Dim strSQLCust As String = "select * from customer;"

Dim strSQLOrder As String = "select * from orders;"

Dim objComm As New OledbCommand()

Dim objAdapter As New OledbDataAdapter()


Dim objRel As DataRelation

Dim strResult As String

Dim rowIndex As Integer = 0


objComm.Connection = objConn

objComm.CommandType = CommandType.Text

objComm.CommandText = strSQLCust

objAdapter.SelectCommand = objComm

objConn.Open()


objComm.CommandText = strSQLOrder

objAdapter.Fill(objDataSet, "Orders")

objRel = New DataRelation("custOrder", objDataSet.Tables("Customer").Columns("cid"), objDataSet.Tables("Orders").Columns("cid"))

objDataSet.Relations.Add(objRel)

Call showChild(rowIndex)

End Sub

Private Sub showChild(ByVal RowIndex)

TextBox1.Text = objDataSet.Tables("customer").Rows(RowIndex).Item("cid")

TextBox2.Text = objDataSet.Tables("customer").Rows(RowIndex).Item("cname")

Dim objOrderRel As DataRelation = objDataSet.Tables("customer").ChildRelations("custOrder")

Dim strResult As String

Dim objChildRow As DataRow

For Each objChildRow In objDataSet.Tables("customer").Rows(RowIndex).GetChildRows(objOrderRel)

strResult = strResult + objChildRow("oid") + " " + objChildRow("odate") + vbCrLf

Next

TextBox3.Text = strResult

End Sub

****Note****: How to prevent EOF error?

Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click

rowIndex += 1

Call showChild(rowIndex)

End Sub

Display Child Records in Grid

• This technique uses the fact that the DataView of a table can be used as a DataSource in binding a data grid.

• Assuming a Customer/Orders relationship, for each customer record:– Use Table object’s Clone method to create a temporary

child table structure.– Use Table object’s ImportRow method to import child

records to the clone table.– Use the clone table’s DefaultView to bind the DataGrid.

Dim objRow As DataRow

Dim drFound As DataRow

drFound = objDataSet.Tables("Customer").Rows("0")

TextBox1.Text = drFound.Item("cid")

TextBox2.Text = drFound.Item("cname")

Dim childTable As DataTable

childTable = objDataSet.Tables("orders").Clone

For Each objRow In drFound.GetChildRows(objOrderRel)

childTable.ImportRow(objRow)

Next

DataGrid1.DataSource = childTable.DefaultView

Binding a ListBox with CodePrivate Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load







ListBox1.DataSource = objDataSet.Tables("Customer")

ListBox1.DisplayMember = "CID"

End Sub

Private Sub ListBox1_SelectedIndexChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles ListBox1.SelectedIndexChanged

TextBox1.Text = ListBox1.SelectedItem.item("cname")

End Sub

Note: The FieldName for the DisplayMember is case-sensitive and should match the field name in the database.

Creating Parameter Queries

• 1. Specify the parameters in the SQL statement.– Dim strSQLOrder As String = "select * from orders where cid= ?;"

• 2. Add the parameters to the Command Object’s Parameters collection.– objComm.Parameters.Add("?cid", OleDbType.VarChar)

• 3. Assign the command to Adapter’s SelectCommand – objAdapter.SelectCommand=objComm

• 4. Set parameter’s value.– objAdapter.SelectCommand.Parameters("?cid").Value =

ListBox1.SelectedItem.item("cid")

Parameter Query Example TextBox1.Text = ListBox1.SelectedItem.item("cname") Dim strConn As String = "Provider=Microsoft.Jet.OLEDB.4.0;Data Source = c:\sales2k.mdb" Dim objConn As New OleDbConnection(strConn) objConn.Open() Dim strSQLOrder As String = "select * from orders where cid= ?;" Dim objComm As New OleDbCommand() Dim objAdapter As New OleDbDataAdapter() Dim objDataSet As New DataSet() objComm.Connection = objConn objComm.CommandType = CommandType.Text objComm.CommandText = strSQLOrder objComm.Parameters.Add("?cid", OleDbType.VarChar) objAdapter.SelectCommand = objComm objAdapter.SelectCommand.Parameters("?cid").Value = ListBox1.SelectedItem.item("cid") objAdapter.Fill(objDataSet, "Orders") DataGrid1.DataSource = objDataSet DataGrid1.DataMember = "orders"

Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load Dim strSQLOrder As String = "select * from customer where city= ?;" Dim objComm As New OleDbCommand() Dim objDataSet As New DataSet() objComm.Connection = objConn objComm.CommandType = CommandType.Text objComm.CommandText = strSQLOrder objComm.Parameters.Add("?city", OleDbType.VarChar) objAdapter.SelectCommand = objComm End Sub Private Sub RadioButton_CheckedChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles RadioButton1.CheckedChanged, RadioButton2.CheckedChanged, RadioButton3.CheckedChanged Dim ObjDataView As New DataView() Dim city As String If RadioButton1.Checked = True Then city = "sf" ElseIf RadioButton2.Checked Then city = "la" Else city = "new york" End If objAdapter.SelectCommand.Parameters("?city").Value = city objDataSet.Clear() objAdapter.Fill(objDataSet, "cust") DataGrid1.DataSource = objDataSet DataGrid1.DataMember = "cust" End Sub

• Can we use child table’s view to display child records in a grid?

– Use View’s FilterDim ObjDataView As New DataView()

ObjDataView.Table = objDataSet.Tables(“Orders")

ObjDataView.RowFilter = “cid='" & ListBox1.SelectedItem.item("cid") & "'"


Multiple Forms: Where to import the oledb, and where to create the oledb objects

Imports System.Data.OleDbModule Module1 Public strConn As String = "Provider=Microsoft.Jet.OLEDB.4.0;Data Source = c:\sales2k.mdb" Public objConn As New OleDbConnection(strConn) Public strSQLCust As String = "select * from customer;" Public strSQLOrder As String = "select * from orders;" Public objComm As New OleDbCommand() Public objAdapter As New OleDbDataAdapter() Public objDataSet As New DataSet() Public objRel As DataRelation Public strResult As String Public rowIndex As Integer = 0 Public ObjDataView As New DataView() Public Sub main() objComm.Connection = objConn objComm.CommandType = CommandType.Text objComm.CommandText = strSQLCust objAdapter.SelectCommand = objComm objConn.Open() objAdapter.Fill(objDataSet, "Customer") objComm.CommandText = strSQLOrder objAdapter.Fill(objDataSet, "Orders") End SubEnd Module

Using ToolBox/Data to Define Ado.Net Objects

• Connection: ToolBox/Data/OledbConnection– ConnectionString

• Command: ToolBox/Data/OledbCommand– Connection– CommandType– CommandText

Using DBMS Views

• Create views (queries) with DBMS

• Create commands to select records from views.

Introduction to ADO.NET Programming. ADO.NET Objects Data Set.NET Applications Data Reader Command...

Documents

Transcript of Introduction to ADO.NET Programming. ADO.NET Objects Data Set.NET Applications Data Reader Command...