I noticed that in the current cvs of fpc it's implemented the master/detail relation between TDataset(s).
I saw that TDetailDataLink and TMasterDataLink was introduced but I couldn't figure how is supposed to work. I also noticed the abscense of NestedDatasets and DataSetField properties.

I'd be glad if someone could explain how the design works and what is expected from a TDataset descendant that support it. I'll try to implement it in TSqliteDataSet.

Thanks in advance.

Luiz

They are not yet implemented. But NestedDataset and DatasetField are ONLY for TClientDataset, and we don't support TClientDataset (yet).

I'd be glad if someone could explain how the design works and what is expected from a TDataset descendant that support it.

Nothing is expected, i.e. TDataset does not implement anything concerning master/detail. How could it ?

I'll try to implement it in TSqliteDataSet.

What you must do is

1. Implement parameter support (TParams/TParam is present).

2. Introduce a Datasource property. Whenever the Datasource changes it's data, the detail dataset most close, fill in new parameters, and reopen.

2 is not a problem, this is max 50 lines of code. 1 is the problem.

Michael.

They are not yet implemented. But NestedDataset and DatasetField are ONLY for TClientDataset, and we don't support TClientDataset (yet).

Not only, they were first implemented for Oracle object field and they're used by some other custom implementation, for example InstantObject exposers use them for accessing parts (subobjects).

I began to rewrite something similar for fpc some week ago, I hope to continue soon.

Not yet that is.
With NestedDataset in Delphi you could.

> I'll try to implement it in TSqliteDataSet.

We could collaborate. Maybe you could create a Sqllite broker for InstantObject (http://www.instantobjects.org/) too. Just now the core part of InstantObject (i.e. without presentation) works in fpc.

Bye Uberto

So none of the current TDataset descendants works with Master/Detail schema ?
If some works, can anybody send me a example?

But NestedDataset and DatasetField are ONLY for TClientDataset, and we don't support TClientDataset (yet).

At least TDataset class in Delphi 7 has both properties.

I'll take a look.
Thanks.

Luiz.

Uberto Barbini wrote

We could collaborate. Maybe you could create a Sqllite broker for InstantObject (http://www.instantobjects.org/) too. Just now the core part of InstantObject (i.e. without presentation) works in fpc.

I'd be happy in helping, but i don't have enough time. Sorry.

Luiz

BTW:

To Michael Van Canneyt:

Did you notice the patch i sent privately to you Yesterday?

Luiz

MasterDetail works, and you don't need NestedDatasets or DataSetFields for that.

1. Put a Master dataset and a Datasource on a form, connect them and fill the properties.
2. Put a Detail dataset and a Datasource and connect them.
3. In Detail dataset set 3 properties: Index, Master dataset, and Master fields.
That's all

Alex

Then how does TDataset know how to load itself from a TDatasetField ? There is no code in DB.Pas to do this.

In TClientDataset, it's just a blob with a complete data package in it, but the definition of this packages only makes sense to another TClientDataset.

TDatasetProvider has a mechanism to pack a 'traditional' Master/Detail dataset (e.g. using TQuery) into a TClientDataset packet for the Master with a TDatasetField containing the data from the detail dataset...

A horrible mechanism, but it works more or less.

Yes, but TNestedDataset is a BDE implementation.
It uses a proprietary format.

The bottom line is that at the TDataset level, there exists only TDatasetField. You need to create a descendent of TDataset to access the data in a TDatasetField, and TClientDataset or TNestedDataset are standard Delphi TDatasets which do this.

Michael.

Yes. I didn't apply it yet; I will do so tonight.
I had lots of other things to do.

Michael.

Thank you. It seems that you refering to TDbf which is the only that has these properties.

Luiz

Luiz Américo wrote

Thank you. It seems that you refering to TDbf which is the only that has these properties.

Not really.
The Zeos components have this properties too. ;)