ADO - Can I edit results of a complex query with multiple join statements?

Question

I'm working on a data conversion utility which can push data from one master database out to a number of different databases. The utility its self will have no knowledge of how data is kept in the destination (table structure), but I would like to provide writing a SQL statement to return data from the destination using a complex SQL query with multiple join statements. As long as the data is in a standardized format that the utility can recognize (field names) in an ADO query.

What I would like to do is then modify the live data in this ADO Query. However, since there are multiple join statements, I'm not sure if it's possible to do this. I know at least with BDE (I've never used BDE), it was very strict and you had to return all fields (*) and such. ADO I know is more flexible, but I don't know quite how flexible in this case.

Is it supposed to be possible to modify data in a TADOQuery in this manner, when the results include fields from different tables? And even if so, suppose I want to append a new record to the end (TADOQuery.Append). Would it append to two different tables?

The actual primary table I'm selecting from has a complimentary table which is joined by the same primary key field, one is a "Small" table (brief info) and the other is a "Detail" table (more info for each record in Small table). So, a typical statement would include something like this:

select ts.record_uid, ts.SomeField, td.SomeOtherField from table_small ts
join table_detail td on td.record_uid = ts.record_uid

There are also a number of other joins to records in other tables, but I'm not worried about appending to those ones. I'm only worried about appending to the "Small" and "Detail" tables - at the same time.

Is such a thing possible in an ADO Query? I'm willing to tweak and modify the SQL statement in any way necessary to make this possible. I have a bad feeling though that it's not possible.

Compatibility:

1. SQL Server 2000 through 2008 R2
2. Delphi XE2

Answer 1

I have abandoned the original idea of live ADO query updates, as it has become more complex than I can wrap my head around. The scope of the data push project has changed, and therefore this is no longer an issue for me, however still an interesting subject to know.

The new structure of the application consists of attaching multiple "Field Links" on various fields from the original set of data. Each of these links references the original field name and a SQL Statement which is to be executed when that field is being imported. Multiple field links can be on one single field, therefore can execute multiple statements, placing the value in various tables, etc. The end goal was an app which I can easily and repeatedly export a common dataset from an original source to any outside source with different data structures, without having to recompile the app.

However the concept of cached updates was not appealing to me, simply for the fact pointed out in the link in RBA's answer that data can be changed in the database in the mean-time. So I will instead integrate my own method of customizable data pushes.

Answer 2

Editing these Fields which have no influence on the joins is usually no problem. Appending is ... you can limit the Append to one of the Tables by

procedure TForm.ADSBeforePost(DataSet: TDataSet);
begin
  inherited;
  TCustomADODataSet(DataSet).Properties['Unique Table'].Value := 'table_small';
end;

but without an Requery you won't get much further. The better way will be setting Values by Procedure e.g. in BeforePost, Requery and Abort.

If your View would be persistent you would be able to use INSTEAD OF Triggers

Answer 3

Jerry,

I encountered the same problem on FireBird, and from experience I can tell you that it can be made(up to a small complexity) by using CachedUpdates . A very good resource is this one - http://podgoretsky.com/ftp/Docs/Delphi/D5/dg/11_cache.html. This article has the answers to all your questions.