I guess I asked the wrong question before :'(   Pascal databases
lazarus / 21-General

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OC DelGuy · 2021-01-07 04:13

Previously I asked about controls to display pascal records.  I
thought I needed the controls in  the "Data Controls", "Data Access",
and "SQLdb" tabs.  Turns out you need a database program to use them
and they seem pretty complex.
And, as far as I can gather, the database table seems to be created in
the database program and not in the Pascal code!

I have an existing database I created with Pascal Types:
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 type  Item
= record    Description : String;    Quan : Byte;    Price : Real; 
end; var  Inventory : array[1..2000] of Item;
How can I display these records in a GUI program?

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speter · 2021-01-07 04:20

Have a look at some of the documents relating to database oriented
(lazarus) programming, including
https://wiki.freepascal.org/Lazarus_Database_Overview
and
https://wiki.freepascal.org/SQLdb_Tutorial0  (there are at least 4
tutorials)

Quote from: OC DelGuy on January 07, 2021, 05:13:28 amI have an
existing database I created with Pascal Types...
Can you please explain what you mean by the above!?

cheers
S.

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lucamar · 2021-01-07 04:51

Quote from: OC DelGuy on January 07, 2021, 05:13:28 amI have an
existing database I created with Pascal Types:
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 type  Item
= record    Description : String;    Quan : Byte;    Price : Real; 
end; var  Inventory : array[1..2000] of Item;
How can I display these records in a GUI program?
Did you do it with normal, flat-file access? as in:

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 var 
MyDatabase: file of Item;{... etc...}  Write(MyDatabase,
Inventory[i]);  { and so on }
Then you'll have to either move it to a more "formal" database (say, a
SQLite one, or even a TBufDataset) or read the data normally and use
normal (non-database) controls. This last is not difficult (much less
if your data set is really that small): just react to some event (e.g.
a key or button press), write or read your "database" and populate
some controls with the data.

It realy depends on exactly what you want to do: if it's just to show
records as in a TDBGrid you could populate a TStringGrid instead, if
to edit the data record by record, some TLabels, TEdits and TButtons,
and so on.

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PascalDragon · 2021-01-07 08:17

Quote from: OC DelGuy on January 07, 2021, 05:13:28 amHow can I
display these records in a GUI program?

You could implement something like CSVDataset for your custom database
format (the unit is relatively short and should be understandable) and
then you can use the database controls without problems. The main
“magic” is inside TCSVDataPacketReader.ReadNextRow and
TCSVDataPacketReader.LoadFieldDefs.

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MarkMLl · 2021-01-07 10:08

Quote from: PascalDragon on January 07, 2021, 09:17:59 amQuote from:
OC DelGuy on January 07, 2021, 05:13:28 amHow can I display these
records in a GUI program?

You could implement something like CSVDataset for your custom database
format (the unit is relatively short and should be understandable) and
then you can use the database controls without problems. The main
“magic” is inside TCSVDataPacketReader.ReadNextRow and
TCSVDataPacketReader.LoadFieldDefs.

That could be a fun general-purpose project. I've been working on a
parser for a particular type of binary file which I implemented
cautiously on a byte-by-byte basis so as to be able to report
accurately on unexpected EOF etc., and I'd imagine that something like
that could be made into a component with a formatting template or
language definition provided at runtime and diagnostics to a stream.

MarkMLl

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wp · 2021-01-07 10:08

I guess you are a beginner: you should forget about databases, nothing
to get started!

You always talk about "displaying" data. Therefore a stringgrid is
absolutely sufficient for this purpose. I am attaching a simple demo
project which creates some dummy inventory items and displays them in
a grid. Try to understand every line of this project, I added lots of
comments. Ask what you don't understand.

This demo creates the inventory by code. In the next step you should
read the inventory from a file. But I thought it is more motivating
when the first step gives you something to see.