Friday, 29 November 2013

How to use TpFIBDataSet, TpFIBQuery and TpFIBTransaction FIBPlus components to connect with Firebird / Interebase database in Delphi XE4?

How to use TpFIBDataSet, TpFIBQuery and TpFIBTransaction FIBPlus components to connect with Firebird / Interebase database in Delphi XE4?

Following is the basic article on Firebird / Interbase database connectivity in Delphi XE4 using FIBPlus database components like TpFIBDataSet, TpFIBQuery and TpFIBTransaction. I will explain all these FIBPlus database components in detail. I have written a small article on TpFIBDatabase before this article. Please go through that before reading this one. Read FIBPlus TpFIBDatabase...

FIBPlus TpFIBQuery Component

An application works with a database by issuing SQL instructions. They are used to get and modify data\metadata. FIBPlus has a special TpFIBQuery component responsible for SQL operator execution. This robust, light and powerful component can perform any actions with the database. 

TpFIBQuery is very easy-to-use: just set the TpFIBDatabase component, fill in the SQL property and call any ExecQuery method (ExecQueryWP, ExecQueryWPS). 

NOTE: The tpFIBQuery is not a TDataset descendant, so it does not act in exactly the same way or exhibit the same methods / properties as you would expect to find in a dataset. 

The example below will show how to create TpFIBQuery dynamically at run-time and thus get data about clients.

 var sql: TpFIBQuery;
 sql := TpFIBQuery.Create(nil);
 with sql do
 try
 Database := db;
 Transaction := db.DefaultTransaction;
 SQL.Text := 'select first_name, last_name from customer';
 ExecQuery;
 while not Eof do begin
 Memo1.Lines.Add(
 FldByName['FIRST_NAME'].AsString+' '+
 FldByName['LASTST_NAME'].AsString);
 Next; end;
 sql.Close;
 finally
 sql.Free;
 end;

FIBPlus TpFIBDataSet component

The TpFIBDataSet component is responsible for work with datasets. It is based on the TpFIBQuery component and helps to cache selection results. TpFIBDataSet is a TDataSet descendant so it supports all TDataSet properties, events and methods.

TpFIBDataSet enables you to select, insert, update and delete data. All these operations are executed by TpFIBQuery components in TpFIBDataSet. 

To select data you set the SelectSQL property. It’s similar to setting the SQL property of the QSelect component (TpFIBQuery type). Define the InsertSQL.Text property to insert data, UpdateSQL.Text to update, DeleteSQL.Text to delete and RefreshSQL.Text to refresh the data. 

Here is a demo database employee.gdb (or .fdb for Firebird) to show how to write Select SQL and get a list of all employees. I will write all queries in InsertSQL, UpdateSQL, etc.

with pFIBDataSet1 do begin
 if Active then Close;

 SelectSQL.Text := 'select CUST_NO, CUSTOMER, CONTACT_FIRST, CONTACT_LAST from CUSTOMER';

 InsertSQL.Text := 'insert into CUSTOMER(CUST_NO, CUSTOMER, CONTACT_FIRST,                                           CONTACT_LAST )' + 
                              ' values (:CUST_NO, :CUSTOMER, :CONTACT_FIRST, :CONTACT_LAST)';

 UpdateSQL.Text := 'update CUSTOMER set CUSTOMER = :CUSTOMER, '+
                   'CONTACT_FIRST = :CONTACT_FIRST, CONTACT_LAST = :CONTACT_LAST '+
                   'where CUST_NO = :CUST_NO';

 DeleteSQL.Text := 'delete from CUSTOMER where CUST_NO = :CUST_NO';

 RefreshSQL.Text := 'select CUST_NO, CUSTOMER, CONTACT_FIRST, CONTACT_LAST '                                       + 'from CUSTOMER where CUST_NO = :CUST_NO';

 Open;
end;

To open TpFIBDataSet either execute Open/OpenWP methods or set the Active property to True. To close TpFIBDataSet call the Close method

FIBPlus TpFIBTransaction component

A transaction is an operation of database transfer from one consistent state to another. All operations with the dataset (data/metadata changes) are done in the context of a transaction. To understand special FIBPlus features completely you need to know about InterBase / FIBPlus transactions. 

All the changes done in the transaction can be either committed (in case there are no errors) by Commit or rolled back (Rollback). Besides these basic methods TpFIBTransaction has their context saving analogues: CommitRetaining and RollbackRetaining, i.e. on the client side, these will not close a TpFibQuery or TpFibDataset.

To start the transaction you should call the StartTransaction method or set the Active property to True. To commit the transaction call Commit/CommitRetaing, to roll it back - Rollback/RollbackRetaining. 

TpFIBQuery and TpFIBDataSet components have some properties which help to control transactions automatically. In particular they are: the TpFIBDataSet.AutoCommit property; the poStartTransaction parameter in TpFIBDataSet.Options; qoStartTransaction and qoCommitTransaction in TpFIBQuery.Options.

TpFIBTransaction has three basic transaction types: 
tpbDefault, 
tpbReadCommited, 
tpbRepeatableRead. 

At design time you can also create special types of your own in the TpFIBTransaction editor and use them as internal ones. Set the transaction type to set its 
parameters:

TpbDefault – parameters must be set in TRParams
tbpReadCommited – shows the ReadCommited isolation level
tbpRepeatableRead – shows the RepeatableRead isolation level 

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