[fpc-pascal] The new book: "WEB and database programming with fpc and Lazarus for newbies and professionals"

[Martin Schreiber]

On Wednesday 16 June 2010 20:10:09 Burkhard Carstens wrote:

This is for MSEide+MSEgui:

>
> chapter 1 - Database programming
>
> First, I created a desktop app to play with the database. All the DB
> components on a DataModule and some DBGrid, DBNavigator on a form.
> * First problem:
> Data changes in the grid don't get to the database.
> * Solution:
> in SQLQueryTimes.OnAfterPost add:
>    SQLQueryTimes.ApplyUpdates;
>    SQLTransactionTimes.CommitRetaining;
>
Activate tmsesqlquery.controller.options dso_autoapply and dso_autocommitret.

> * Next problem:
> When doing "insert, post, edit (the inserted row), post" the data
> doesn't get to DB.
> * Found reason:
> The primary key is an auto-increment. It is added by postgres when
> inserting the record, but not reported back. Therefore, the following
> Update statement uses (probably?) "UPDATE .. WHERE times_id = NULL .."
> while times_id actually got a non-NULL value in the DB. So the update
> statement does nothing, not even reporting an error.
> * Solution:
> none. According to http://bugs.freepascal.org/view.php?id=16076 this is
> not yet implemented.

Use a sequence generator in the DB in order to build the primary key value. 
Place a tsequencelink (tab DBf) into the datamodule, select database 
datasource and datafield, fill in the 'sequencename' property.

>
> * Next Problem:
> The "projects" are stored in a second table with id, name and some other
> info. Now I'd like to see (and deal with) the projects name instead of
> its ID in the times_grid. Some keywords came to memory: "Master/
> Detail", "Lookup" and "JOIN" ..
[...]
>
> * Solution:
> none, at least not the way I intended. Seems like DBGrid is not (yet)
> able to offer a LookupCombo in a cell like Delphi does. (After I found
> out, I also saw the related bug report .. ) I got something working
> with a separate DBLookupList next to the grid ..
>
Use tdbwidgetgrid (tab DBe), place a tdbenumeditdb into the lookup column (tab 
DBe). Alternative for better performance with very big lookup datasets: 
tdbenumeditlb (tab DBe) and tdblookupbuffer (tab DB).

Martin