Migrating from DBGo (ADO) to FireDAC

In my last blog I explained how to migrate from DBExpress to FireDAC. Here I will show you how to migrate a client-server application using ADO data access components, such as TADOConnection, TADOQuery, TADOTable, 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.

So lets start in steps.

1. Units Changed

We need to replace used ADO units to FireDAC units.

Find 

ADODB

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. ADO components classes compatible with FireDAC

Search ADO classes and replace with FireDAC classes

ADO	FireDAC
TADOConnection	TFDConnection
TADOTable	TFDTable
TADOQuery	TFDQuery
TADOStoredProc	TFDStoredproc
TADOCommand	TFDCommand

3. Other Types classes changed

Search ADO classes and replace with FireDAC classes

ADO	FireDAC
TParams	TFDParams
TBlobStream	TFDBlobStream
TBDEDataSet	TFDRDBMSDataSet

4. TADOConnection -> TFDConnection Properties

Search ADO classes and replace with FireDAC classes

ADO	FireDAC
ConnectionTimeout	Not Supported.
ConnectOptions	Not Supported.
CursorLocation	Not Supported.
DefaultDatabase	Not Supported.
IsolationLevel	Not Supported.
KeepConnection	ResourceOptions.KeepConnection
Provider	DriverName

Note* - OnLogin Event

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

5. TADOTable -> TFDTable Properties

Search ADO classes and replace with FireDAC classes

ADO	FireDAC
CommandTimeOut	Not Supported
ConnectionString	Not supported
CursorLoacation	Not supported
CursorType	FetchOptions.CursorKind
ExecuteOptions	Not Supported
EnableBCD	Not supported
LockType	UpdateOptions.LockMode
MarshallOptions	Not supported
MaxRecords	FetchOptions.RecsMax
Readonly	UpdateOptions.Readonly

6. TADOQuery -> TFDQuery Properties

Search ADO classes and replace with FireDAC classes

ADO	FireDAC
CommandTimeOut	Not Supported
ConnectionString	Not supported
CursorLoacation	Not supported
CursorType	FetchOptions.CursorKind
Datasource	MasterSource Note. Please check MasterFields
ExecuteOptions	Not Supported
EnableBCD	Not supported
LockType	UpdateOptions.LockMode
MarshallOptions	Not supported
MaxRecords	FetchOptions.RecsMax
ParamCheck	ResourceOptions.Paramcreate
Parameters	Params

7. TADOStoredProc -> TFDStoredProc     Properties

Search ADO classes and replace with FireDAC classes

ADO	FireDAC
CommandTimeOut	Not Supported
ConnectionString	Not supported
CursorLoacation	Not supported
CursorType	FetchOptions.CursorKind
Datasource	MasterSource Note. Please check MasterFields
ExecuteOptions	Not Supported
EnableBCD	Not supported
LockType	UpdateOptions.LockMode
MarshallOptions	Not supported
MaxRecords	FetchOptions.RecsMax
ParamCheck	ResourceOptions.Paramcreate
Parameters	Params
ProcedureName	StoredProcName

8. TADOCommand -> TFDCommand        Properties

Search ADO classes and replace with FireDAC classes

ADO	FireDAC
CommandTimeOut	Not Supported
CommandType	CommandKind
ConnectionString	Not supported
ExecuteOptions	Not Supported
ParamCheck	ResourceOptions.Paramcreate
Parameters	Params

9. 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//

10. 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;

11. 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.

Clientdataset1.Data := FDQuery.Data; //will result an error //

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;

12. Extra points to check

a. 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)

b. Check SQL statement for “. If it is like “DBA.Segments” which is wrong then it should be “DBA”.”Segment” or DBA.Segments