Q) What is the use of UDL files in Delphi?

Ans. If you want to store the server connection information outside the application which can be retrieved later during connecting time. This is very useful in creating UDL files which are very helpful where hard coded connection string is not acceptable. Also try to save the documents in the form of .udl which will help you to connect databases easily.

Q) What is the procedure to access the database from Delphi ?

Ans. - To access the database the BDE needs to be configured as it defines an alias for the database that has to be connected. 

- The configuration allows the avoidance of coding the directory path and it just takes the referring of the alias. 

- The creation of three objects is required to access the database and that includes: Query or table object that in synchronization with the alias and it also fetches some data. 

- Data source object that allows the linking between the data and the controls used to connect the database. 

- Setting the active property on the table or query to TRUE will open the database and allow the accessing to be done.

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