ADO .NET – part II

1. ADO .NET – part II August 2004 [ Marmagna Desai]

2. CONTENTS • ADO vs ADO .NET • ADO .NET – Managed providers • Connecting to Database • SqlConnection • Selecting Database • SqlCommand • SqlDataReader • Inserting Data • SqlCommand • Datasets • Selecting Data • Updating Data • Conclusion

3. ADO vs ADO .net • Ultimate goal of ADO and ADO.net is same: Providing data access API. • Though there are many differences. • ADO relies on COM • ADO.net relies on “managed-providers” defined by CLR

4. ADO vs ADO .net ……[cont] • Main Differences:

5. ADO vs ADO .net ……[cont] • Connection Model: • ADO: • Client application needs to be connected always to data-server while working on the data. • These results in open connections for long time and thus data can not be accessed in parallel. • ADO .NET • Client disconnects connection immediately the data is processed. This will cache data at client side to achieve better performance. Hence ADO .net creates “disconnected version of RecordSet object

6. ADO vs ADO .net ……[cont] • Data Representation: • Recordsets are generated one per table. This does not support hierarchical structure of data access. It will be programmer’s responsibility to define relationships among different recordsets. • Rercordsets can not support data accessing from multiple sources. Above limitations are resolved by implementation of Dataset objects in ADO.net mode

7. ADO vs ADO .net ……[cont] • Data Passing: • ADO objects communicate in binary mode hence it will be really difficult to pass data across firewalls. • ADO .net use XML for passing data

8. ADO .net Managed Providers • ADO .net provides following three classes • DBConnection • DBCommand • DBDataReader • These classes are never used directly. The inherited set of classes called “managed providers” are used for different functionalities of data access

9. ADO .net Managed Providers • These are the different providers • Provider optimized for SQL 7 • OLE – DB provider • A generic ODBC provider • Provider for Oracle • These providers gathers information on various data sources and how to interact with them • E.g. SQL data provider uses private protocol (tabular data stream) to provide information and access methods on SQL server.

10. Connecting to Database • Following methods are very similar to ADO. They are connection oriented and hence leave open connection while retrieving the data from source. • SQL managed provider contains the class called SqlConnection. • This class is used to connect to the sql database. • Code: [ Please see next slide]

11. Code….. • Dim connStr as String = “server=localhost;uid=uid;pwd=pwd;database=northwind;" Dim conn as New SqlConnection (connStr) Conn.Open() “Access Data Records Conn.Close() • This is very similar to ADO program. Only the SqlConnection will be replaced with ADODB.Connection.

12. Selecting Data • SqlCommand class is defined in ADO .net to provide different functionalities like insert,update,delete etc. on selected database. • It is similar to ADODB.Command class in ADO. • SqlCommand retrieves and place data on objects called SqlDataReader • SqlCommand does this using ExecuteReader() method. [Please see next slide for Code]

13. Code • Dim conn As SqlConnection = Nothing Try conn = New SqlConnection(connStr) Dim cmd As New SqlCommand("Select StateCode, " & "StateName From States", conn) conn.Open() Dim reader As SqlDataReader = _ cmd.ExecuteReader(CommandBehavior.CloseConnection) Me.ddRegion.DataSource = reader Me.ddRegion.DataBind() Me.ddRegion.Items.Insert(0, New ListItem("Select One:", "")) Catch exp As Exception lblOutput.Text = "Error occurred: " + exp.Message Finally If (conn.State <> ConnectionState.Closed) Then conn.Close() End Try

14. Explanation • A connection is made using SqlConnection • SqlCommand is used to construct a query • ExecuteReader is used to generate SqlDataReader object • Bind data to DropDownList Server name ddRegion

15. Inserting Data • SqlCommand can be used to perform insert,delete,update etc. operations on data. • ExecuteNonQuery method is used for this purpose. • This method does not allow results to return to the database. [Please see code in next slide]

16. Code • Dim conn As New SqlConnection(connStr) Dim cmd As New SqlCommand("CustInsert", conn) cmd.CommandType = CommandType.StoredProcedure cmd.Parameters.Add("@CustomerID", Me.txtCustomerID.Text) cmd.Parameters.Add("@Name", Me.txtName.Text) cmd.Parameters.Add("@Company", Me.txtCompany.Text) cmd.Parameters.Add("@Title", Me.txtTitle.Text) cmd.Parameters.Add("@Address", Me.txtAddress.Text) cmd.Parameters.Add("@City", Me.txtCity.Text) cmd.Parameters.Add("@Region", Me.ddRegion.SelectedValue) cmd.Parameters.Add("@Zip", Me.txtZip.Text) 

17. Code ….[cont] Try conn.Open() cmd.ExecuteNonQuery() lblOutput.Text = "Your information was successfully saved!" Catch exp As Exception lblOutput.Text = "An error occurred:" + exp.Message Finally 'Ensure connection is closed If (conn.State <> ConnectionState.Closed) Then conn.Close() End Try

18. Datasets • Datasets are new to ADO .net. • It access data in Disconnected in maner • It stores data in-memory and process it.

19. Datasets….[cont] • Following are main features • Datasets does not interact with data source directly. • Data adapter is used to fill this gap. : SqlDataAdapter class • SqlDataAdapter class provides functionalies such as insert, delete and update. • SqlDataAdapter also provides method called Fill() which is used to fill up the Dataset. • Once dataset is filled with data, it can define relationships among gathered data from different source. • Dataset uses XML to transmit data among different components. • Different views of data stored in dataset can be created using dataview calss.

20. Code • Following code shows how to query database using SqlDataAdapter and fill the Dataset. Dim conn As SqlConnection = Nothing Try conn = New SqlConnection(connStr) ‘Create DataAdapter Dim da As New SqlDataAdapter("Select StateCode, " & _ "StateName From States", conn) ‘Create DataSet Dim ds As New DataSet ‘Fill DataSet da.Fill(ds, "States")

21. Code …cont ‘Access a DataTable in the DataSet and create a bindable view Dim view As DataView = ds.Tables(0).DefaultView Me.ddRegion.DataSource = view Me.ddRegion.DataBind() Me.ddRegion.Items.Insert(0, New ListItem("Select One:", "")) Catch exp As Exception lblOutput.Text = "Error occurred: " + exp.Message Finally If (conn.State <> ConnectionState.Closed) Then conn.Close() End Try

22. Conclusion • Basically ADO .net adds following extended capabilities to ADO. • Disconnected modeling • Relational Database query and in-memory storage • Hierarchical structure of data • XML based transmission of data among components These additional features makes ADO .net considerable advancement in Microsoft Technology

23. Q? THANKS!!