[fpc-pascal] Lookup fields in databases
Michael Van Canneyt
michael at freepascal.org
Sat Aug 29 09:11:41 CEST 2015
On Sat, 29 Aug 2015, Marc Santhoff wrote:
> peeking the database code I found that:
> - a TDataSet has FieldDefs
> - fields are described by TFieldDef(s)
> - TField has several special properties like "KeyFields" and
> How are these properties of TField (descendants) set and by whom?
In the IDE designer, by the programmer, or after opening the dataset in code.
> I can imagine the information to set the lookup dataset is stored inside
> the databases metadata using contraints (foreign key references ...).
No, it is not.
> Or are those props for wiring by the programmer manually at design time?
A relation (lookup) doesn't have to exist formally in the database to be used in the IDE.
Since a second dataset is needed, there is no way the code can know which dataset to use.
I do have a project where I have an IDE wizard that uses DB information to construct the
necessary datasets and lookup fields.
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