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Please help me understand u++ schemas [message #1573]

Thu, 09 March 2006 03:48

santiago
Messages: 13
Registered: March 2006
Location: Cï¿½rdoba, Argentina

Promising Member

I really don't get how to use schemas, please excuse me, I've been looking at the code for a while, but i'm not an c++ expert and since it's not documented or commented, it's been really hard for me. So i'm asking for help here.
My problem is that i don't get how to make schemas work, i think i get the idea, created a .sch include it, called it, and i think everyhing is fine, i even get the idea for querys, but can't create a table.
Can someone please give me a hint i'll appreciate it.
Thanks in advance.

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Re: Please help me understand u++ schemas [message #1576 is a reply to message #1573]

Thu, 09 March 2006 04:08

fudadmin
Messages: 1321
Registered: November 2005
Location: Kaunas, Lithuania

Ultimate Contributor
Administrator

santiago wrote on Thu, 09 March 2006 02:48

I really don't get how to use schemas, please excuse me, ...

You don't need to feel sorry for asking questions here on Ultimate++ forums (unlike some other forums). But maybe you should better post some of your code and name the topic "Can't create a table with schemas"? Smile

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Re: Please help me understand u++ schemas [message #1580 is a reply to message #1576]

Thu, 09 March 2006 05:30

mirek
Messages: 13975
Registered: November 2005

Ultimate Member

fudadmin wrote on Wed, 08 March 2006 22:08

santiago wrote on Thu, 09 March 2006 02:48

I really don't get how to use schemas, please excuse me, ...

Agree, this is way too generic question. The simple way is to zip your test package and post here.

Mirek

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Re: Please help me understand u++ schemas [message #1581 is a reply to message #1580]

Thu, 09 March 2006 05:45

fudadmin
Messages: 1321
Registered: November 2005
Location: Kaunas, Lithuania

Ultimate Contributor
Administrator

Off topic: When do you sleep, Mirek ? Shocked

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Re: Please help me understand u++ schemas [message #1582 is a reply to message #1581]

Thu, 09 March 2006 05:50

mirek
Messages: 13975
Registered: November 2005

Ultimate Member

fudadmin wrote on Wed, 08 March 2006 23:45

Off topic: When do you sleep, Mirek ? Shocked

And you?

Mirek

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Re: Please help me understand u++ schemas [message #1594 is a reply to message #1573]

Thu, 09 March 2006 13:31

santiago
Messages: 13
Registered: March 2006
Location: Cï¿½rdoba, Argentina

Promising Member

Thank you for the really quick answers.

Here's the code of the SQL_Sqlite3 example that i don't understand.

SQL = sqlite3;

SqlSchema sch(SQLD_SQLITE3);
StdStatementExecutor se(sqlite3);

All_Tables(sch);

if(sch.ScriptChanged(SqlSchema::UPGRADE))
    Sqlite3PerformScript(sch.Upgrade(),se);
	
if(sch.ScriptChanged(SqlSchema::ATTRIBUTES)) {
	Sqlite3PerformScript(sch.Attributes(),se);
}
	
if(sch.ScriptChanged(SqlSchema::CONFIG)) {
	Sqlite3PerformScript(sch.ConfigDrop(),se);
	Sqlite3PerformScript(sch.Config(),se);
}
	
sch.SaveNormal();

The "SQL = sqlite3;" line even has a comment above saying "What does this do?"

Thanks again for the help.

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Re: Please help me understand u++ schemas [message #1598 is a reply to message #1594]

Thu, 09 March 2006 15:20

mirek
Messages: 13975
Registered: November 2005

Ultimate Member

SQL is "default SQL cursor" - one main cursor, useful for apps dealing with just one database. That line in fact defines that this default cursor will refer to created SqlLite session.

Now those scripts. U++ is able to generate a couple of database scripts from the .sch files:

* script that creates schems tables by adding individual columns

"adding individual columns" is quite imporant, as that way you are able to "upgrade" existing database schema in most cases - you just run the script, statements for existing columns will fail, but those that are not there yet will succed and upgrade schema

* script to add "attributes" to columns - attributes here are constraints or indexes

* script to drop "attributes" - note that this is often useful and harmless to stored data to recreate attributes (drop + add).

* script to wipe the schema out - seldom used and not present in the example

* script to perform initial setting of table content - for configuration tables etc...

All_Tables here creates those scripts - they are stored in Strings inside "sch".

Now performing script can be quite long operation, something you do not want to do each time you start your code. That is the reason for "ScriptChanged" - it tests whether script differs from the one stored inside "exe-directory".

"SaveNormal" then stores scripts into exe-dir.

Note that those script issues are usually present only in debug code. When delivering application, you can either execute scripts from exe-dir, or you can run debug version against customers database engine (recently, I prefer later).

Anything left to explain?

Mirek

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