aspnet aspnet Accessing data with ADO.NET Accessing data with ADO.NET Hà Đồng Hưng Objectives • Introduction – ADO.NET and other technologies • Connected Objects – Objects List – Demonstrations – Using Disconnected Objects in VS.NET • Disconnected Objects – Objects List – Demonstrations – Using Disconnected objects in VS.NET Objectives • Introduction – ADO.NET and other technologies • Connected Objects – Objects List – Demonstrations – Using Disconnected Objects in VS.NET • Disconnected Objects – Objects List – Demonstrations – Using Disconnected objects in VS.NET What is ADO.NET ? • ADO.NET is a set of libraries included with the Microsoft .NET Framework that help you communicate with various data stores from .NET applications – connecting to a data source – submitting queries – processing results • Can also use ADO.NET as a hierarchical, disconnected data cache to work with data offline Why a new data access technology? • Visual Basic 3 - Data Access Objects (DAO) – designed to communicate with local file-based databases • Visual Basic 4 - Remote Data Objects (RDO) – a fast, lightweight data access layer designed to talk to larger server-based databases (SQL Server, Oracle…) • Visual Basic 5 and Visual Studio 97 - ODBCDirect – combine the power of RDO with the ease of use that DAO provides • Visual Basic 6 and Visual Studio 6 - ADO – a data access model we could use easily in server-side scripts (fewer lines of code, allow us to pass data structures from server to client and back) Drawbacks of older technologies • Problems: – Developers need to build more powerful applications • work with XML data • can pass ADO Recordset objects between different tiers in your application, but cannot combine the contents of multiple Recordset objects • … – Recent versions of ADO added more XML features, but ADO will never handle XML data as efficiently as ADO.NET) ADO.NET model • ADO.NET is designed to help developers build efficient multi- tiered database applications across intranets and the Internet ADO.NET model • The disconnected half of the ADO.NET object model do not communicate directly with the connected objects • A major change from previous Microsoft data access object models. – In ADO, Recordset object stores the results of your queries. – Call Open method to fetch the results of a query – Call Update method to submit changes stored within the Recordset to your database. • ADO.NET DataSet is comparable in functionality to the ADO Recordset. – However, DataSet does not communicate with your database. – In order to fetch data from your database into a DataSet, you pass the DataSet into the Fill method of a connected ADO.NET object—the DataAdapter. .NET Data Providers • SQL Client .NET Data Provider – communicate with SQL Server databases, version 7+ • OLE DB .NET Data Provider – communicate with various data stores through OLE DB providers • Each .NET data provider implements the same base classes – Base classes: Connection, Command, DataReader, Parameter, Transaction – their actual names depend on the provider Connection Strings • SQL Server – Provider=SQLOLEDB;Data Source=MyServer\MyInstance;  Initial Catalog=MyDatabase;User ID=MyUID;Password=MyPass; – Provider=SQLOLEDB;Data Source=MyServer; Initial Catalog=MyDb; Integrated Security=SSPI; – Provider=SQLOLEDB;Data Source=MyServer; Initial Catalog=MyDatabase; Trusted_Connection=Yes; • Oracle – Provider=MSDAORA;Data Source=MyDatabaseAlias; User ID=MyUID;Password=MyPass; • Access – Provider=Microsoft.Jet.OLEDB.4.0;Data Source=C:\A\MyDb.mdb; – Provider=Microsoft.Jet.OLEDB.4.0;Data Source=Data\MyDb.mdb; – Provider=Microsoft.Jet.OLEDB.4.0;Data Source=C:\A\MyDb.mdb; Jet OLEDB:Database Password=MyPass; [...]... • DataSet Object – contains a set of data – container for a number of DataTable objects – data stored in a DataSet object is disconnected from your database Any changes you make to the data are simply cached in each DataRow – allow you to write to and read from a XML file • DataTable Object – Is used to examine data through collections of rows and columns – can store the results of a query in a DataTable... the data – Use For…Next, While…End While Dim da As New OleDbDataAdapter(strSql, cn) Dim ds As New DataSet da.Fill(ds, “ABC") Dim tbl As DataTable = ds.Tables(“ABC”) Dim row As DataRow For Each row In tbl.Rows i=row(“MAKH”) s=row(“TenKH”) Next row Demonstrations Disconnected Objects • Create DataTable in DataSet Dim ds As New DataSet() Dim tbl As DataTable = ds.Tables.Add("Customers") Dim ds As New DataSet... Objects • Fetch the results of a query into a DataSet strSql = "SELECT MaKH, TENKH FROM KHACHHANG" Dim da As New OleDbDataAdapter(strSql, cn) Dim ds As New DataSet da.Fill(ds, “MAVATENCUAKH") • Get the data returned by DataAdapter Dim da As New OleDbDataAdapter(strSQL, cn) Dim ds As New DataSet() da.Fill(ds, “ABC") Dim tbl As DataTable = ds.Tables(“ABC”) Dim row As DataRow = tbl.Rows(0) Response.Write(“Mã... New DataTable("Customers") ds.Tables.Add(tbl) Demonstrations Disconnected Objects • Create a column in DataTable Dim ds As New DataSet() Dim tbl As DataTable = ds.Tables.Add("Customers") Dim col As DataColumn = tbl.Columns.Add("CustomerID")  Dim ds As New DataSet() Dim tbl As DataTable = ds.Tables.Add("Orders") Dim col As DataColumn = tbl.Columns.Add("OrderID", _ GetType(Integer))  • Use methods DataTable.PrimaryKey,... stores information about the structure of the column • Constraint Object – place constraints on the data stored locally within a DataTable object • DataRelation Object – Is used to indicate a relationship between different DataTable objects in your DataSet • DataView Object Objectives • Introduction – ADO.NET and other technologies • Connected Objects – Objects List – Demonstrations – Using Disconnected... contents of a specific table • DataReader Object (data read-only) – Is designed to help you retrieve and examine the rows returned by your query quickly • Transaction Object • Parameter Object Connected Objects • Data Adapter – act as a bridge between your database and the disconnected objects in the ADO.NET object model – Fill method fetch the results of a query into a DataSet or a DataTable – Update method... the results of a query in a DataTable through the DataAdapter object’s Fill method • DataRow Object – Use the object’s Rows collection – To examine the data stored in a specific column of a particular row, you use the Item property Disconnected Objects • DataColumn Object – corresponds to a column in your table – doesn’t contain the data stored in your DataTable Instead, it stores information about the... cmd.Parameters.Add(“@Param1”,”1”) cmd.Parameters.Add(“@Param2”,”2”) Dim rdr As OleDbDataReader = cmd.ExecuteReader() Tips Connected Objects • In the ADO.NET object model, you should close your DataReader objects as quickly as possible • Connection object having an open DataReader is considered blocked – If open a second DataReader before closing the first one, you’ll receive an exception “requires an... DataTable.PrimaryKey, DataTable.Constraint – To set PrimaryKey (consisting many properties), constraints… Demonstrations Disconnected Objects • Add new data Dim row As DataRow = ds.Tables("Customers").NewRow row("CustomerID") = "ALFKI" ds.Tables("Customers").Rows.Add(row) Dim aValues As Object() = {“123", "A", “B", "007"} ds.Tables("Customers").LoadDataRow(aValues, False) Demonstrations Disconnected Objects • Modify data. .. queries that select data Dim strSql As String strSql = "Select * from KHACHHANG" Dim cmd As New OleDb.OleDbCommand(strSql, cn) Dim rdr As OleDb.OleDbDataReader = cmd.ExecuteReader() While rdr.Read() i = rdr(“MaKH") s = rdr(“TenKH") End While rdr.Close() Demonstrations Connected Objects • Execute queries: Insert, Update, Delete (DML -Data Manipulation Language), Create, Alter, Drop… (DDL -Data Definition . aspnet aspnet Accessing data with ADO. NET Accessing data with ADO. NET Hà Đồng Hưng Objectives • Introduction – ADO. NET and other technologies. Recent versions of ADO added more XML features, but ADO will never handle XML data as efficiently as ADO. NET) ADO. NET model • ADO. NET is designed to help