Database change
lazarus / 16-Databases

----------------------------------------------------------------------
pcurtis · 2021-01-19 19:59

Hi All,

whats the best / correct way to be informed of changes to a DB /
dataset?

I use Zeos and Sqlite

Thanks in advance.

----------------------------------------------------------------------
Zvoni · 2021-01-20 07:04

sqlite itself has a notification callback
https://sqlite.org/c3ref/update_hook.html

----------------------------------------------------------------------
madref · 2021-01-20 08:03

When ever I use a form that has data from my database I use a query to
get the specific data I need from that database.
When that query has changed I update it.


To check if the query is changed I use
Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i   if
TQ_Evaluatie.State in [dsEdit, dsInsert] then  begin   
TQ_Evaluatie.Post;    TQ_Evaluatie.ApplyUpdates;    if
Form_Lint.Trans_RefereeDB.Active then     
Form_Lint.Trans_RefereeDB.CommitRetaining;  end;

----------------------------------------------------------------------
cdbc · 2021-01-20 09:09

Hi
Implement the Observer pattern...
It is built in, in the LCL (TObserved) in TPersistent
You only need to build an Observer, with one method
If need be, "steal" the implementation of TObserved in TPersistent and
put it in your db-code 
Two small classes with enormous effect.
HTH
Regards Benny

----------------------------------------------------------------------
pcurtis · 2021-01-20 10:33

@zvoni - any idea how to implement this in laz / fpc?

----------------------------------------------------------------------
Zvoni · 2021-01-20 12:31

Quote from: pcurtis on January 20, 2021, 11:33:55 am@zvoni - any idea
how to implement this in laz / fpc?
Probably as a class-helper for sqlite3conn (never worked with Zeos).
You should check first if the external function is already declared
available in sqlite3conn (at least that's the place i would look in)
The link describes the prototype of the Function which acts as a
"Event"-Handler. From there......