SQL Helper Class

Microsoft .net framework consists of ADO .NET which enables the developer to interact with the database. ADO .NET provides many rich features that can be used to retrieve and display data in a number of ways. Apart from the flexibility provided by the ADO .NET, sometimes we find ourselves repeating the same code again and again. Consider that at some point in our application we need to pass some parameters and retrieve some information from the database. We can perform this task by writing 5-6 lines of code which is cool. But when later we need to pass the parameters we have to write those 5-6 lines again which is not cool.

Methods

• ExecuteDataset Retrieve multiple rows from the database and return value to DataSet class.

• ExecuteNonQuery Executes a Transact-SQL statement against the connection and returns the number of rows affected
  

• ExecuteNonQueryReturn No return value.
  

• ExecuteReader Retrieve multiple rows from the database and return value to SqlDataReader class.
  

• ExecuteScalar Retrieve a single row instead of group of rows and return value to object.
  

• ExecuteXmlReader Sends the CommandText to the Connection and builds an XmlReader object.

Summary

• It is used for Database Access other than System.Data.SqlClient or System.Data.Oledb

• SqlHelper() - This method used to reduce the lines of connecting the database than when we are using the SqlDataAdapter or OleDbAdapter.

• You can download sql helper dll at this
  

Sample Code

' Very short command
Dim nResult as integer
nResult = Convert.ToInt32(SqlHelper.ExecuteScalar(ConnectionString, CommandType.Text, "Select Count(id) from table"))

Using SqlParameter Class

Represents a parameter to a SqlCommand and optionally its mapping to DataSet columns. This class cannot be inherited.

You should use parameters to filter queries in a secure manner. But I recommend to use parameters when you try to pass the datetime value in your query.

The process of using parameter contains two steps:

• create SqlParameter object and insert there value with applicable properties
• define the parameter in the SqlCommand command string, and assign the SqlParameter object to the SqlCommand object. When the SqlCommand executes, parameters will be replaced with values specified by the SqlParameter object.

Sample Code

Imports Namespace: System.Data.SqlClient

' Insert string
Dim sql As String = " INSERT INTO tblZipCode([ZIPCODE], [STATE], [CITY], [TestDate]) VALUES(@ZIPCODE, @STATE, @CITY), @TestDate"

' Create sql parameter
Dim param(3) As SqlParameter

param(0) = New SqlParameter("@ZIPCODE", SqlDbType.VarChar)
param(0).Value = "60000"

param(1) = New SqlParameter("@STATE", SqlDbType.VarChar)
param(1).Value = "Statename"

param(2) = New SqlParameter("@CITY", SqlDbType.VarChar)
param(2).Value = "Cityname"

' Recommend to use sql param when you try to send datetime value
param(3) = New SqlParameter("@TestDate", SqlDbType.DateTime)
param(3).Value = DateTime.Now

' Create Connection string
Dim sConnection As New SqlConnection("server=(local);uid=sa;pwd=pass;database=db")
sConnection.Open()

' Create Sql Command
Dim command As SqlCommand = sConnection.CreateCommand()
command.CommandText = sql

' Add Parameter to command
command.Parameters.AddRange(param)

' Execute command
Dim nResult As Integer = command.ExecuteNonQuery()

If nResult > 0 Then
Console.WriteLine("Insert completed")
End If

sConnection.Close()
command.Dispose()

SqlCommand Methods

ExecuteNonQuery

• Overridden. Executes a Transact-SQL statement against the connection and returns the number of rows affected.

ExecuteReader

• Overloaded. Sends the CommandText to the Connection and builds a SqlDataReader.

ExecuteScalar

• Overridden. Executes the query, and returns the first column of the first row in the result set returned by the query. Additional columns or rows are ignored.

ExecuteXmlReader

• Sends the CommandText to the Connection and builds an XmlReader object.

Populate a DataSet from a Database

SqlDataAdapter class represents a set of data commands and a database connection that are used to fill the DataSet and update a SQL Server database. This class cannot be inherited.

Getting data from a database is easy, and working with data is easier than before. The most important concept to remember is that the DataSet is a data structure separate and distinct from a data store. Although you get data from a database in this example, it doesn't matter where the data comes from; the DataSet will always present a consistent programming model. It is a simple collection of data with relational database characteristics. There is no Load, Open, or Execute on a DataSet because it doesn't know where it gets its data from. This section describes how to use a SqlDataAdapter to get data from a database into a DataSet.

Sample Code (with MsSql)

Dim sConnection As String = "server=(local);uid=sa;pwd=password;database=yourDatabase"

Dim objDataAdapter As New SqlDataAdapter("Select * From tableName", sConnection)
Dim dsResult As New DataSet("Result")

If Not IsNothing(objDataAdapter) Then
' Fill data into dataset
objDataAdapter.Fill(dsResult)

objDataAdapter.Dispose()
End If

' Test by bind data into datagridview control
Me.DataGridView1.DataSource = dsResult.Tables(0)

Retrieving Data Using the DataReader

You can use the ADO.NET DataReader to retrieve a read-only, forward-only stream of data from a database. Results are returned as the query executes, and are stored in the network buffer on the client until you request them using the Read method of the DataReader. Using the DataReader can increase application performance both by retrieving data as soon as it is available, rather than waiting for the entire results of the query to be returned, and (by default) storing only one row at a time in memory, reducing system overhead.

The DataReader class in .NET provides similar functions to SQL Cursors, which are actually not supported in the .NET Framework. DataReades are used to efficiently retrieve a forward-only stream of data from a database. DataReaders are appropriate when the need is to simply display the result set, as only one record at a time is ever present in memory. The DataReader is mainly used in scenarios wherein data need not be updateable nor should persist across multiple requests.

Sample Code (with MsSql)
You must import SqlClient .

Imports System.Data.SqlClient

Dim sConnection As String = "server=(local);uid=sa;pwd=PassWord;database=DatabaseName"

Dim objCommand As New SqlCommand
objCommand.CommandText = "Select * From tablename"
objCommand.Connection = New SqlConnection(sConnection)
objCommand.Connection.Open()

Dim objDataReader As SqlDataReader = objCommand.ExecuteReader()

If objDataReader.HasRows Then
Do While objDataReader.Read()
Console.WriteLine(" Your name is: " & Convert.ToString(objDataReader(0)))
Loop
Else
Console.WriteLine("No rows returned.")
End If

objDataReader.Close()
objCommand.Dispose()