Migrating from BDE to FireDAC

In my last blog I explained about FireDAC, its features and how it will help our Delphi Application’s performance improvements. But still lots of Delphi Applications are using BDE, IBExpress and ADO for DB connectivity and for data access. So when we migrate a Delphi application from old version to new version, I think we should also migrate data accesss components to FireDAC. So in this blog I will explain how to migrate a simple client-server application using BDE data access components, such as TDatabase, TQuery, TTable, to the FireDAC. It shows the basic principles of replacing the common components, properties and code, preserving the developers working time and avoiding the common migration pitfalls. Delphi makes migration over the decades relatively painless, however, this doesn’t mean effortless!.

So lets start in steps.

1. Units Changed

We need to replace used BDE units to FireDAC units.

Find 

DBTables   or  Bde.DBTables

Replace

         FireDAC.Stan.Intf, FireDAC.Stan.Option, FireDAC.Stan.Error, FireDAC.UI.Intf, FireDAC.Phys.Intf, FireDAC.Stan.Def, FireDAC.Phys, FireDAC.Stan.Pool, FireDAC.Stan.Async, FireDAC.Stan.Param, FireDAC.DatS, FireDAC.DApt.Intf, FireDAC.DApt, FireDAC.Comp.Client, FireDAC.Comp.DataSet

2. BDE components classes compatible with FireDAC

Search BDE classes and replace with FireDAC classes

BDE	FireDAC
TSession	TFDManager
TDatabase	TFDConnection
TTable	TFDTable
TQuery	TFDQuery
TStoredProc	TFDStoredproc
TUpdateSQL	TFDUpdateSQL
TBatchMove	TFDDatamove

3. Other Types classes changed

Search BDE classes and replace with FireDAC classes

BDE	FireDAC
TParams	TFDParams
TBlobStream	TFDBlobStream
TBDEDataSet	TFDRDBMSDataSet

4. BDE Exception class change

Search BDE classes and replace with FireDAC classes

BDE	FireDAC
EDBEngineError	EFDDBEngineException

5. TSession -> TFDManager Properties

Search BDE classes and replace with FireDAC classes

BDE	FireDAC
AutosessionName	Not Supported so remove.
KeepConnection	ResourceOptions.KeepConnection
NetFileDir	Not Supported so remove.
PrivateDir	Not Supported so remove.
SessionName	Not Supported so remove.

  

6. TDatabase -> TFDConnection Properties

Search BDE classes and replace with FireDAC classes

BDE	FireDAC
AliasName	ConnectionDefName
DatabaseName	ConnectionName
Exclusive	Not Supported so remove.
HandleShared	Not Supported so remove. Note. Please check LibHandle at runtime.
SessionName	Not Supported so remove.
KeepConnection	ResourceOptions.KeepConnection
Readonly	UpdateOptions.Readonly

Note* - OnLogin Event

Tdatabase.OnLogin event is different than TFDConnection.OnLogin. So we should remove Tdatabase event and re-write TFDConnection Event.

7. TTable -> TFDTable Properties

Search BDE classes and replace with FireDAC classes

BDE	FireDAC
Autorefresh	UpdateOptions.RefreshMode = onDemand
DatabaseName	ConnectionName Connection Note. Please replace with Connection for better understanding.
Exclusive	Not Supported so remove.
Readonly	UpdateOptions.Readonly
TableType	Not Supported so remove.
UpdateMode	UpdateOptions.UpdateMode
SessionName	Not Supported so remove.

8. TQuery -> TFDQuery Properties

Search BDE classes and replace with FireDAC classes

BDE	FireDAC
Autorefresh	UpdateOptions.RefreshMode = onDemand
DatabaseName	ConnectionName Connection Note. Please replace with Connection for better understanding.
Datasource	MasterSource Note. Please check MasterFields
ParamCheck	ResourceOptions.Paramcreate
Requestlive	UpdateOptions.Requestlive
Unidirectional	UpdateOptions.Unidirectional
UpdateMode	UpdateOptions.UpdateMode
SessionName	Not Supported so remove.

9. TStoredProc -> TFDStoredProc Properties

Search BDE classes and replace with FireDAC classes

BDE	FireDAC
Autorefresh	UpdateOptions.RefreshMode = onDemand
DatabaseName	ConnectionName Connection Note. Please replace with Connection for better understanding.
SessionName	Not supported so remove

10. Sorting

FireDAC components like TFDQuery, TFDTable does not have Sort property. So we have to use IndexFieldNames property for sorting. So where ever we have used Sort for sorting in our project we need to replace with IndexFieldNames like follow.

ADQuery1.IndexFieldNames := 'ORDERID';

or

ADQuery1.IndexFieldNames := 'OrderDate:D;Price'; //D for descending//

11. TBookMark Changes for Dataset components

When we save a bookmark for future use we must use pointer for

var

BookMark : Pointer;

CDS : TClientDataset

……

// Required so your assignment doesn't attempt to free a non-existent bookmark //

 Bookmark := nil;

 TBookmark(Bookmark) := CDS.GetBookmark;

12. Data Property

If we use TFDQuery and ClientDataset together then Data property is mostly used to assign saved data to any other dataset component directly instead of using any loop. Here TFDQuery have also Data property but type is different. Earlier in TADOQuery or other Query component, Data property was OleVariant type which was same type like ClientDataset but now it is IFDDataSetReference.

So we cannot just assign directly like.

//will result an error //

Clientdataset1.Data := FDQuery.Data; 

Above code will compile successfully but will result “Invalid data packet” error at runtime.

In this scenario we have to use TDatasetProvider as mediator to transfer data from once dataset to another. We can use DatasetProvider.Data property like follow.

DataSetProvider1.Dataset := FDQuery1;

FdQuery1.Open;

Clientdataset1.data := DatasetProvider1.data;

13. Extra points to check

Need to change some numeric fields to TBCDFields when it will show error and set Size=2 when in Database field type is like number(15,2)