Uniquery + DataSetProvider + ClientDataSet Master Detail

[rrcanalista]

Hi, I have the follow components

UniQuery1 -> DataSetProvider1 -> ClientDataSet1 (Master) -> DataSource1

UniQuery2 -> DataSetProvider2 -> ClientDataSet2 (Detail) -> DataSource2

ClientDataSet2.MasterSource = DataSource1
ClientDataSet2.MasterField = 'MasterID'
ClientDataSet2.IndexFieldNames = 'DetailMasterID'

When I open the both, they work but if navigate in the CDS1 shows the exception "Key Violation"

I have set Providerflags correctly of the CDS and Uniquery and shows the same error.
So, what's the best way to make master/detail in this scenario?

[AlexP]

Hello,

Please specify your versions of UniDAC, IDE, and the name of the DB your are working with. In addition, send a project demonstrating the problem to alexp*devart*com (including scripts for creating and filling tables).

[rrcanalista]

Hi, I realize that the error shows when the detail is empty.

unidac 4.6.11 Delphi XE2 using Firebird 2.5.

I sent a project sample with the database DEMO.fdb

[AndreyZ]

Thank you for the information. We have reproduced the problem and investigation of the problem is in progress. As soon as we have any results, we will let you know.
As a workaround, you can set the PacketRecords option of the detail TClientDataSet component to -1.

[rrcanalista]

Thank you for the information. It works, another question, is there any performance problem if I use CDS2.PacletRecord=-1 instead 0? is this the really right way to make master/detail with clientdataset?

[AndreyZ]

No, there is no performance problems when using PacketRecord = -1 for the detail TClientDataSet. dbExpress technology uses PacketRecord = -1 for the detail TClientDataSet internally when fetches data for it.
Yes, it is a correct way of establishing of master/detail relationships using TClientDataSet components.

[Johan.Swart]

Hi,

Could you perhaps post your example of using ClientDataSet with the UniDAC components in a master detail setup.

I would very like to learn from your example.

Alternatively, please email me [email protected]

Regards,
Johan Swart

[rrcanalista]

Hi, no problem, I have send to you the Demo.

[AndreyZ]

We thoroughly investigated this question. The 'Key Violation' error occurs because of a bug in the TCustomClientDataSet.CheckDetailRecords method (it is declared in the DBClient unit). When PacketRecords is set to 0, TClientDataSet must load only metadata, but instead it loads all data of the detail table from the server to its buffer. The following code demonstrates this:

Code: Select all

AddDataPacket(DoGetRecords(-1, RecCount, 0, '', MasterValues), False); // as you can see, -1 (all records) is used instead of 0 (metadata only)

When the detail table is empty, TClientDataSet initiates another request to the server. Again, all data of the detail table are fetched from the server and TClientDataSet tries to put it to its buffer. Because all records are already in the buffer, it violates the primary key constraint. This causes the 'Key Violation' error. The same error occurs when using the standard components, you can check it yourself. In this case, the only solution is to set PacketRecords to -1.