Overview of ADO.NET Architecture

Chapter Learning Objectives

• ADO.NET Architecture
• Connection class
• Command and Data Reader Class
• DataAdapter and DataTable class
• DataSet class
• Provider Agnostic code

ADO.NET Architecture

ADO.NET uses a multilayer architecture that mainly has a few concepts, for instance Connection, Reader, Command, Adapter and Dataset objects. ADO.NET introduced data providers that are a set of special classes to access a specific database, execute SQL commands and retrieve data. The Data providers are extensible. Developers can create their own providers for a proprietary data source. There are some examples of data providers such as SQL Server providers, OLE DB and Oracle provider.

ADO.NET provides the following two types of classes objects:

• Connection-based: They are the data provider objects such as Connection, Command, DataAdapter and DataReader. They execute SQL statements and connect to a database.
  
  
• Content-based: They are found in the System.Data namespace and includes DataSet, DataColumn, DataRow and DataRelation. They are completely independent of the type of data source.

ADO.NET Namespaces

Namespaces	Description
System.Data	Contains the definition for columns,relations,tables,database,rows,views and constraints.
System.Data.SqlClient	Contains the classes to connect to a Microsoft SQL Server database such as SqlCommand, SqlConnection and SqlDataAdapter.
System.Data.Odbc	Contains classes required to connect to most ODBC drivers. These classes include OdbcCommand and OdbcConnection.
System.Data.OracleClient	Contains classes such as OracleConnection and OracleCommand required to connect to an Oracle database.

                                                                  Table 1.1 ADO.NET Namespace

Connection Class

You need to establish a connection class object for inserting, updating, deleting and retrieving data from a database. The Connection class allows you to establish a connection to the data source. The Connection class object needs the necessary information to discover the data source and this information is provided by a connection string.

Connection Strings

You need to supply a connection string in the Connection class object. The connection string is a series of name/value settings separated by semicolons (;). A connection string requires a few peices of information such as the location of the database, the database name and the database authentication mechanism.

This connection is used to connect to the Master database on the current computer using integrated security (indicating the currently logged-in Windows user can access the database).

C# Code

string conString = "Data Source=localhost;Initial Catalog=Master;Integrated Security=SSPI";

In the case if integrated security, it is not supported and then the connection must indicate a valid user name and password combination as in the following.

C# Code

string conString = "Data Source=localhost;Database=Master;user id=sa;password=sa";

If you use the OLE DB provider than your connection string will need some additional settings that identify OLE DB drivers such as:

C# Code

string conString = "Data Source=localhost;Initial Catalog=Master;user id=sa;password=;Provider=MSDAORA";

You can specify the details of the connection strings in the global application settings file and then you can retrieve your connection string by name from the ConfigurationManager as in the following.

App.Config

<configuration>
    <connectionStrings>
        <add name="Master" connectionString ="Data Source=localhost;Initial Catalog=Master;Integrated Security=SSPI" />
    </connectionStrings>
</configuration>

Once you declare all the details in the App.config file that pertains to the Connection string then you can use this definition in the code file also as in the following.

C# Code

string conSting = ConfigurationManager.ConnectionStrings["Master"].ConnectionString ;
SqlConnection Conn = new SqlConnection(conSting);

Testing a Connection

Once you have configured the right connection string to establish connectivity with the specific data source you simply use the Open() and Close() methods as in the following.

C# Code

private void Form1_Load(object sender, EventArgs e)
{
    string conSting =         ConfigurationManager.ConnectionStrings["Master"].ConnectionString ;
    SqlConnection Conn = new SqlConnection(conSting);

    try
    {
        Conn.Open();
        textBox1.Text = "Server Version=" + Conn.ServerVersion;
        textBox1.Text += "Connection Is=" + Conn.State.ToString();
    }
    catch (Exception err)
    {
        textBox1.Text = err.Message;
    }
    finally
    {
        Conn.Close();
        textBox1.Text += "Connection Is=" + Conn.State.ToString();
    }
}

You can also use the SqlConnectionStringBuilder class to configuration a connection string rather than specifying it in the App.Config file as in the following.

C# Code

SqlConnectionStringBuilder obj = new SqlConnectionStringBuilder();
obj.DataSource = "localhost";
obj.InitialCatalog = "Master";
obj.IntegratedSecurity = true;
SqlConnection Conn = new SqlConnection(obj.ConnectionString);

Important: Connections are a limited server resource so it is imperative to release the open connection as soon as possible.

Command and Data Reader Classes

The Command Class allows performing any data definition tasks such as creating and altering tables and databases, retrieving, updating and deleting of records. The Command object used to execute SQL queries can be inline text or a Stored Procedure. It is all dependent on the type of command you are using. Before using the command, you need to configure the Command Type, Text and Connection properties as in the following.

C# Code

//Command Class definition
SqlCommand sc = new SqlCommand();
sc.Connection = Conn;
sc.CommandType = CommandType.Text;
sc.CommandText = query;

Alternatively you can pass the connection argument directly to the Command class as in the following.

C# Code

//Command Class definition
SqlCommand sc = new SqlCommand(query,Conn);

In the following example, we are creating a window application form with a Text Box control. We are establishing a connection to the Customer table from the AdventureWorks database. Then, using the SqlDataReader class, we will go through all the records of the table and display the FirstName and LastName in the TextBox control by executing the While() loop as in the following.

C# Code

private void Form1_Load(object sender, EventArgs e)
{
    //Connection String
    SqlConnectionStringBuilder obj = new SqlConnectionStringBuilder();
    obj.DataSource = "localhost";
    obj.InitialCatalog = "AdventureWorksLT2008";
    obj.IntegratedSecurity = true;

    // Add Connection string to SqlConnection
    SqlConnection Conn = new SqlConnection(obj.ConnectionString);

    // Query to retrieve records from AdventureWorks Database
    string query = "select FirstName,LastName from SalesLT.Customer";

    //Command Class definition
    SqlCommand sc = new SqlCommand();
    sc.Connection = Conn;
    sc.CommandType = CommandType.Text;
    sc.CommandText = query;

    SqlDataReader sdr = null;
    try
    {
       //Open connection
        Conn.Open();
        sdr = sc.ExecuteReader();

        //Get all records
        while(sdr.Read())
        {
            textBox1.AppendText(sdr.GetValue(0) + "\t" + sdr.GetValue(1));
            textBox1.AppendText("\n");
        }

    }
    catch (Exception err)
    {
        textBox1.Text = err.Message;
    }
    finally
    {
        //Release reader and connection object
        sdr.Close();
        Conn.Close();
    }
}

It is important to release the objects of the Reader class manually after the job is done or you can set the CommandBehaviour Property to CloseConnection in the ExcuteReader() method to be avoid the burdon of manually releasing the object as in the following.

C# Code

//Automatically releasing the Reader class Object
sdr = sc.ExecuteReader(CommandBehavior.CloseConnection);

DataReader Class

The DataReader Class object allows you to read the data returned by a SELECT command by a simple forward-only and read-only cursor. It requires a live connection with the data source and provides a very efficient way of looping and consuming all parts of the result set. The object of the DataReader cannot be directly instantiated. Instead you must call the ExecuteReader method of the Command object and close the connection when you are done using the Data Reader, otherwise the connection remains alive until it is explicitly closed.

DataReader with ExecuteReader() Method

Once you have the DataReader you can cycle through its records by calling the Read() method in a while loop. This moves the row cursor to the next record.

C# Code

//Open connection
Conn.Open();
sdr = sc.ExecuteReader(CommandBehavior.CloseConnection);

//Get all records
while(sdr.Read())
{
  textBox1.AppendText(sdr.GetValue(0) + "\t" + sdr.GetValue(1));
  textBox1.AppendText("\n");
}

ExecuteScalar() Method

The ExecuteScalar() method returns the value stored in the first field of the first row of a result set generated by the command's SELECT query. This method is usually used to count the total number of rows in the table as in the following.

C# Code

private void Form1_Load(object sender, EventArgs e)
{
    //Connection String
    string conString = @"Data Source=localhost;Database=AdventureWorksLT2008;Integrated Security=SSPI";

    // Add Connection string to SqlConnection
    SqlConnection Conn = new SqlConnection(conString);

    // Query to retrieve records from AdventureWorks Database
    string query = "select COUNT(*) from SalesLT.Customer";

    //Command Class definition
    SqlCommand sc = new SqlCommand(query, Conn);

    //Open connection
    Conn.Open();
    int CountCustomer = (int)sc.ExecuteScalar();

    //Count all records
    textBox1.AppendText("Total Customer=\t" + CountCustomer.ToString());
}

ExecuteNonQuery() Method

The ExecuteNonQuery() method executes commands that don't return a result set, for instance INSERT, UPDATE and DELETE. Here in this example we made a modification to a specific record in the Customer table of the Adenture Works database.

C# Code

private void Form1_Load(object sender, EventArgs e)
{
    //Connection String
    string conString = @"Data Source=localhost;Database=AdventureWorksLT2008;Integrated Security=SSPI";

    // Add Connection string to SqlConnection
    SqlConnection Conn = new SqlConnection(conString);

    // Query to retrieve records from AdventureWorks Database
    string query = @"update AdventureWorksLT2008.SalesLT.Customer
                    set FirstName='ajay'
                    where CustomerID=2";

    //Command Class definition
    SqlCommand sc = new SqlCommand(query, Conn);

    //Open connection
    Conn.Open();

    //Reflect changes into database
    int CountCustomer = sc.ExecuteNonQuery();

    //Result
    MessageBox.Show("Record Update Successfully");
}

DataAdapter and DataTable class

A DataAdapter bridges the gap between the disconnected DataTable objects and the physical data source. The SqlDataAdapter is capable of executing a SELECT, DELETE and UPDATE statement on a data source as well as extracting input from the result set into a DataTable object. The SqlDataAdapter class provides a method called Fill() to copy the result set into the DataTable.

C# Code

private void Form1_Load(object sender, EventArgs e)
{
    //Connection String
    string conString = "Data Source=localhost;Database=AdventureWorksLT2008;Integrated Security=SSPI";

    // Add Connection string to SqlConnection
    SqlConnection Conn = new SqlConnection(conString);

    // Query to retrieve records from AdventureWorks Database
    string query = "select FirstName,LastName from SalesLT.Customer";

    //Command Class definition
    SqlCommand sc = new SqlCommand(query, Conn);

    // Data Adapter definition
    SqlDataAdapter sda = new SqlDataAdapter(sc);

    // filling the result set in data table
    DataTable dt = new DataTable();
    sda.Fill(dt);

    //output in data grid
    dataGridView1.DataSource = dt.DefaultView;
}

These are the commonly used properties offered by the SqlDataAdapter class as in the following:

 

Property	Description
SelectCommand	This command executed to fill in a Data Table with the result set.
InsertCommand	Executed to insert a new row to the SQL database.
UpdateCommand	Executed to update an existing record on the SQL database.
DeleteCommand	Executed to delete an existing record on the SQL database.

                                                                     Table 1.2 Data Adapter Properties

SelectCommand Example

C# Code

// Query to retrieve records from AdventureWorks Database
string query = "select FirstName,LastName from SalesLT.Customer";

//Command Class definition
SqlCommand sc = new SqlCommand(query, Conn);

// Data Adapter definition
SqlDataAdapter sda = new SqlDataAdapter();
sda.SelectCommand = sc;

// filling the result set in data table
DataTable dt = new DataTable();
sda.Fill(dt);

Update Command Example

C# Code

string query = @"update AdventureWorksLT2008.SalesLT.Customer
set FirstName='ajay'
where CustomerID=2";

//Command Class definition
SqlCommand sc = new SqlCommand(query, Conn);

// Data Adapter definition
SqlDataAdapter sda = new SqlDataAdapter();
sda.UpdateCommand = sc;

Parameterized Commands (Stored Procedure)

A Stored Procedure is a batch of one or more SQL Statements that are stored in the database. They are similar to a function in that they are well-encapsulated blocks of the logic that accept data using an input parameter and return data via result set or output parameter. The following is the SQL code needed to create a procedure for extracting a single something from the customer table on behalf of a specific CustomerID.

Sql.script

Create Proc GetCustomer
@CustID varchar(10)
AS
select * from SalesLT.Customer where CustomerID=@CustID
GO

Next you can create a SqlCommand to wrap the call to the Stored Procedure. This command takes one parameter as input and returns the records. A parameterized command is basically something that uses a placeholder in the SQL text. The placeholder indicates dynamically supplied values that are then sent using a parameters collection of the Command object as in the following.

C# Code

private void btnData_Click(object sender, EventArgs e)
{
    //Connection String
    string conString = "Data Source=localhost;Database=AdventureWorksLT2008;Integrated Security=SSPI";

    // Add Connection string to SqlConnection
    SqlConnection Conn = new SqlConnection(conString);

    //Command Class definition
    SqlCommand sc = new SqlCommand("GetCustomer", Conn);
    sc.CommandType = CommandType.StoredProcedure;

    sc.Parameters.Add("@CustID",txtParameter.Text);

    // Data Adapter definition
    SqlDataAdapter sda = new SqlDataAdapter(sc);

    // filling the result set in data table
    DataTable dt = new DataTable();
    sda.Fill(dt);

    //output in data grid
    dataGridView1.DataSource = dt.DefaultView;
}

This example uses a parameterized command that is supplied via text box (Customer ID) and the result is processed using the Stored Procedure in the code file and the result is displayed in the Data Grid View control as in the following:



DataSet class

A DataSet is a disconnected architecture technology. It contains zero or more tables and relationships. When you work with a dataset, the data in the data source is not touched at all. Instead all the changes are made locally to the dataset in memory. In the following example you will see how to retrieve data from a SQL Server table and use it to fill in a DataTable object in the DataSet.

C# Code

private void Form1_Load(object sender, EventArgs e)
{
    //Connection String
    string conString = "Data Source=localhost;Database=AdventureWorksLT2008;Integrated Security=SSPI";

    // Add Connection string to SqlConnection
    SqlConnection Conn = new SqlConnection(conString);

    string query = "select * from SalesLT.Customer";

    //Command Class definition
    SqlCommand sc = new SqlCommand(query, Conn);

    // Data Adapter definition
    SqlDataAdapter sda = new SqlDataAdapter();
    sda.SelectCommand = sc;

    //data Set definition
    DataSet ds = new DataSet();

    // filling the result set in data table
    sda.Fill(ds, "SalesLT.Customer");

    //output in data grid
    dataGridView1.DataSource = ds.Tables["SalesLT.Customer"];
}

Here you need create an empty DataSet and use the SqlDataAdapter Fill() method to execute the query and place the results in a new DataTable in the DataSet.



Provider Agnostic code

You can use a single factory object to create every other type of provider-specific object that you need. You can then interact with these provider specific objects in a completely generic way using a set of base common classes.

Important: You need to import the System.Data.Common namespace in the C# code file for utilizing provider geneal code functionality.

The first step is to setup the App.Config file with the connection string, provider name and the query for this example as in the following.

App.Config

<?xml version="1.0" encoding="utf-8" ?>
<configuration>
    <connectionStrings>
        <add name="Adventure" connectionString ="Data Source=localhost;Database=AdventureWorksLT2008;Integrated Security=SSPI" />
    </connectionStrings>
    <appSettings>
        <add key ="factory" value="System.Data.SqlClient" />
        <add key="CustQuery" value ="select * from SalesLT.Customer"/>
    </appSettings>
</configuration>

Next here is the factory based code:

C# Code

private void Form1_Load(object sender, EventArgs e)
{
    //Get the Factory
    string factory = ConfigurationManager.AppSettings["factory"];
    DbProviderFactory pro = DbProviderFactories.GetFactory(factory);

    //Use this factory to create a connection
    DbConnection con = pro.CreateConnection();
    con.ConnectionString = ConfigurationManager.ConnectionStrings["Adventure"].ConnectionString;

    //Create the command
    DbCommand cmd = pro.CreateCommand();
    cmd.CommandText = ConfigurationManager.AppSettings["CustQuery"];
    cmd.Connection = con;

    //Open the connection
    con.Open();
    DbDataReader rdr = cmd.ExecuteReader();

    //Get all records
    while (rdr.Read())
    {
        textBox1.AppendText(rdr.GetValue(3) + "\t" + rdr.GetValue(5));
        textBox1.AppendText("\n");
    }

}