[Lazarus] Master/detail relationships: what am I missing?

[michael.vancanneyt at wisa.be]

On Mon, 17 Dec 2012, Reinier Olislagers wrote:

> Hi all,
>
> I've been looking into how to use master/detail setups in Lazarus (aka
> tables with foreign keys).
>
> Based on Delphi docs I started writing up & testing this:
>> See also
>> http://docwiki.embarcadero.com/RADStudio/XE3/en/Establishing_Master-detail_Relationships_Using_Parameters
>> Use one connection, 1 transaction, but 2 queries, 2 data sources
>> Example from the Firebird EMPLOYEE database (as used in the SQLDB Tutorials):
>> - a CUSTOMER table with an integer primary key CUST_NO and other fields
>> - a SALES table with a CUST_NO integer field that is a foreign key linking to the CUST_NO field in the CUSTOMER table
>> - a master query selects from the CUSTOMER table
>> - a detail query that selects from the SALES table
>>
>> In the detail query:
>> - set the database property as usual
>> - set the datasource property to point to the master datasource
>> - in the query SQL, use a WHERE query to limit the select; use a parameter with the name of the field in the master table
>> SELECT * from SALES WHERE SALES.CUST_NO=:CUST_NO
>> FPC will now see this as a reference to the current value of CUST_NO in the CUSTOMER (master) query. This is made possible by the fact that the master datasource keeps track of the current record for the master query
>>
>> Make sure that the master query is open before the detail query so it can look up fields.
>>

>> No need for further code, e.g. to specify default values for the SALES.CUST_NO field when adding records.

This is wrong. There is a need. This should still be specified.

>
> I get the form with a combobox for the master field and details grid to
> run without issue and can insert items in the detail grid but the
> foreign key to the master table is null for that record.

Correct. You must enter these values yourself in the AfterInsert of the
detail dataset.

Michael.