what is TADOQuery component for Delphi?

TADOQuery component is aimed at execution of SQL-commands. It can be considered as an analog of TSQLQuery component from dbExpress. Connection to the database is set via Connection or ConnectionString properties. Query text is written to SQL property. If a query returns the dataset one should use Open() method or Active=true property. If a query does not return the dataset, it shall be run using ExecSQL method. ExecSQL returns the number of records processed during a query running. The same value is contained in RowsAffected property.

What is TADOConnection in Delphi

TADOConnection component connects to the data storage. TADOConnection resembles TSQLConnection component. The difference between them is that when working with TSQLConnection connection parameters are set via ConnectionName, DriverName and Paramsproperties. In TADOConnection all connection parameters are set via ConnectionString property. Moreover, it is possible to specify file name with connection parameters as a connection string in TADOConnection.

Connection String with Firebird database in Delphi XE2

procedure TForm1.Button1Click(Sender: TObject);
var 
 Conn: TSQLConnection;
begin
  Conn := TSQLConnection.Create(Self);
  try
    Conn.DriverName := 'Provider=MSDASQL.1; '+
                       'Persist Security Info=False; '+
                       'Data Source=DataBaseName; '+
                       'Initial Catalog=DataBaseName';'; 
    Conn.Params.Add('User_Name=SYSDBA');
    Conn.Params.Add('Password=masterkey');

    // Replace the dbname in the next line with the
    // value obtained at runtime, as  in
    // Conn.Params.Add('Database=' + YourNewPathAndDBName);
    Conn.Params.Add('Database=D:\FolderName\DataBaseName.fdb');

    Conn.Open;
    if Conn.Connected then
      ShowMessage('Connection successfully made to DB');
  finally
    Conn.Free;
  end;
end;

Q :- What is the difference between the SuperServer, classic and embedded servers ?

Ans:-SuperServer is a single-process multi-threaded server (like Apache on Windows, for example) Classic is a multi-process single-threade server - things are synced via a separate lock manager process Embedded is a DLL you hook up to your application and work with database file directly

SuperServer is good for OLTP, lot of users, etc. Classic is good for OLAP or few users running heavy queries. Embedded is good for desktop apps.

You should install and use SuperServer while developing, since embedded only allows one connection at a time, so you cannot access the database from your application and administration tool at the same time. Later, you can deploy using any of those 3 architectures.

Simple Application in VB.Net

Public Class Form1
    Dim sqlconnection As New System.Data.SqlClient.SqlConnection
    Dim sqlCommand As New System.Data.SqlClient.SqlCommand
    Dim sqlDataAdapter As New System.Data.SqlClient.SqlDataAdapter
    Dim cmdBuilder As System.Data.SqlClient.SqlCommandBuilder
    Dim dsDataset As New DataSet
    Dim cmCurrency As CurrencyManager
    Dim LastUID As Integer = 0
    Dim newrow As DataRow

    Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
        Dim dt As New DataTable
        sqlconnection.ConnectionString = "Data Source=Manoj;Initial Catalog=imported_data;User ID=sa;Password=sa"
        sqlCommand.CommandText = "select * from mstcompanies"
        sqlCommand.Connection = sqlconnection
        sqlDataAdapter.SelectCommand = sqlCommand

        cmdBuilder = New System.Data.SqlClient.SqlCommandBuilder(sqlDataAdapter)
        sqlDataAdapter.Fill(dt)
        DataGridView1.DataSource = dt

        txtUID.Text = dt.Rows(0).Item(0)
        txtName.Text = dt.Rows(0).Item(2)
        txtAddress.Text = dt.Rows(0).Item(4)
        txtCity.Text = dt.Rows(0).Item(5)

        dsDataset.Tables.Add(dt)
        dsDataset.Tables(0).TableName = "mstcompanies"
        sqlDataAdapter.TableMappings.Add(New System.Data.Common.DataTableMapping("Table", "mstCompanies"))

        Call bindFields(dt)
        cmCurrency = BindingContext(DataGridView1.DataSource, DataGridView1.DataMember)
    End Sub
    Public Function bindFields(ByVal dtSrc As DataTable)
        txtUID.DataBindings.Add("Text", dtSrc, "UID")
        txtName.DataBindings.Add("Text", dtSrc, "Name")
        txtAddress.DataBindings.Add("Text", dtSrc, "Address")
        txtCity.DataBindings.Add("Text", dtSrc, "City")
    End Function

    Private Sub btnNew_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnNew.Click
        txtUID.Text = ""
        txtName.Text = ""
        txtAddress.Text = ""
        txtCity.Text = ""

        newrow = dsDataset.Tables("mstCompanies").NewRow
        LastUID = dsDataset.Tables("mstcompanies").Rows(dsDataset.Tables("mstcompanies").Rows.Count - 1).Item("UID")
        txtUID.Text = LastUID + 1
    End Sub

    Private Sub btnSave_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnSave.Click
        With dsDataset.Tables("mstcompanies")

            If txtName.Text = "" Then
                MsgBox("Please Enter Company Name")
                Exit Sub
            End If

            dsDataset.Tables("mstcompanies").Rows.Add(newrow)
            newrow.Item("UID") = txtUID.Text + 1
            newrow.Item("Name") = txtName.Text
            newrow.Item("Address") = txtAddress.Text
            newrow.Item("City") = txtCity.Text

            sqlDataAdapter.Update(dsDataset)
            MsgBox("Record Save Successfully.")


        End With
    End Sub

    Private Sub btnDelete_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnDelete.Click
        cmCurrency.RemoveAt(cmCurrency.Position)
        sqlDataAdapter.Update(dsDataset)
        MsgBox("Record Delete Successfully.")
    End Sub

    Private Sub btnUpdate_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnUpdate.Click
        dsDataset.Tables("mstCompanies").Rows(cmCurrency.Position).Item("Name") = txtName.Text
        dsDataset.Tables("mstCompanies").Rows(cmCurrency.Position).Item("Address") = txtAddress.Text
        dsDataset.Tables("mstCompanies").Rows(cmCurrency.Position).Item("City") = txtCity.Text
        sqlDataAdapter.Update(dsDataset)
        MsgBox("Record Update Successfully.")
    End Sub

    Private Sub btnPrevious_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnPrevious.Click
        cmCurrency.Position = cmCurrency.Position - 1

    End Sub

    Private Sub btnNext_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnNext.Click
        cmCurrency.Position = cmCurrency.Position + 1
    End Sub

    Private Sub btnFirst_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnFirst.Click
        cmCurrency.Position = 0
    End Sub

    Private Sub btnLast_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnLast.Click
        cmCurrency.Position = cmCurrency.Count
    End Sub
End Class

What is a Delphi unit?

A Delphi unit is a separate file used to store procedures and functions. If you know what a form is, a unit is exactly the same, except it has no visual interface. So you can't put windows controls on it like buttons and edit boxes. A form has windows controls and their associated code behind them, a unit only has the code.

They are useful if you have some functions that you use often from many different forms and you only want to write them once. For example:

function LeftStr(const S : String; Index : Integer) : String; 

begin 

If Index <= 0 

then 

Result := '' 

else 

Result := Copy(S, 1, Index); 

end;

function RightStr(const S : String; Index : Integer) : String; 

begin 

If Index > Length(S) 

then 

Result := '' 

else 

Result := Copy(S, Index, (Length(S)-Index+1)); 

end; 

Then you can have your unit's name in a forms uses clause and then use the functions LeftStr and RightStr from several different forms.

What is the function of Inheritance in Delphi?

• The inheritance needs a parent and a child class where the child class inherits the property of the parent class. 
• Child can have their own functions or inherit functions and properties from the parent class. 
•  TFootball child class is the base class and inheriting the properties of TBall class of the parents. 
• For Ex.

var
beachBall : TBall;
soccerBall : TFootball;
begin
beachBall := TBall.Create(5);
soccerBall := TFootball.Create(5, 12);

beachBall.Kick(10);
soccerBall.Kick(10);

ShowMessageFmt('Beach ball is moving at speed : %d',[beachBall.GetSpeed]);
ShowMessageFmt('Soccer ball is moving at speed : %d',[soccerBall.GetSpeed]);
end;

The output is shown as such:
Beach ball is moving at speed: 12
Soccer ball is moving at speed: 12