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lazarus / 16-Databases

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amedeo · 2022-03-27 08:25

Hy people
I have a question to change my application.
My application have a Main form from where I launch child forms by
FormXxx.Show. In every child form there are declaration of Database
(SQLite3), Transaction, Tabs e Datasets.
Is it possible to declare Database information in the  Main form and
use its in the child forms?
I saw that calling Database function from a child form the Database is
seen but not usable.
This is because my ignorance or is it a limit?
Thanks
Amedeo

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Bart · 2022-03-27 08:30

Use a separate datamodule perhaps?

Bart

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amedeo · 2022-03-27 09:35

Not, I do not use data-module just Tabs and Datasets

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amedeo · 2022-03-27 09:41

...  sorry ... I use Tabs and Query with Data-source

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wp · 2022-03-27 09:42

Quote from: amedeo on March 27, 2022, 10:25:09 amIs it possible to
declare Database information in the  Main form and use its in the
child forms?
Never do this. Because it will create a circular dependence between
the child forms and the main form: the main form needs to know the
child forms in order to open them, and the child forms need the main
form in order to access the datasets. Although Pascal can handle this
if done properly, it is a very bad idea because you no longer can test
the individual forms independently of the entire application. I
recently wanted to convert a large Delphi application with about 50
forms to Lazarus; since each form depended on the main form the
conversion can only be tested when everything is completed - I finally
gave up.

Do what Bart told you: Add a datamodule to the project and put all the
database components (connections, queries, datsets) on it. You can
also put the TDataSource on it, but sometimes I find it more
advantageous to have on the forms which need it.

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jcmontherock · 2022-03-27 09:58

You can create a common unit containing all the SQLite access. This
unit could be included in all the forms accessing SQLite. That's not
follow the OOP rules, but it works fine. I did it for an application
multi forms with MySQL successfully. You have to play with some
pointers between units.

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amedeo · 2022-03-28 09:57

Thanks
now I have a lot of mater to think about. ZEN meditation needs.
Amedeo