man Padre::DB (3): An ORLite-based ORM Database API

SYNOPSIS

TO BE COMPLETED

DESCRIPTION

This module implements access to the database that Padre is using to store bits & pieces. It is using "ORLite" underneath, for an easy table scheme discovery at runtime. See below to learn about how to update the database scheme.

Updating database scheme

The database is created at runtime if it does not exist, but we are relying on "Padre::DB::Migrate". To summarize "Padre::DB::Migrate":

We provide scripts to update the database from one revision to another.
"Padre::DB" calls "Padre::DB::Migrate" to apply them in order, starting from the current database revision.

Therefore, in order to update the database, you need to do the following:

Create a script share/timeline/migrate-$i.pl with $i the next available integer. This script will look like this:
```
        use strict;
        use Padre::DB::Migrate::Patch;
        # do some stuff on the base
        do(<<'END_SQL');
        <insert your sql statement here>
        END_SQL
```
Of course, in case of dropping an existing table, you should make sure that you don't loose data - that is, your script should migrate existing data to the new scheme (unless the whole feature is deprecated, of course).
Update the user_revision in "Padre::DB"'s call to "Padre::DB::Migrate" to read the new script number (i.e., the $i that you have used to name your script in the timeline directory).
```
        use Padre::DB::Migrate 0.01 {
            [...]
                user_revision => <your-revision-number>,
            [...]
        };
```
Once this is done, you can try to load Padre's development and check whether the table is updated correctly. Once again, check whether data is correctly migrated from old scheme to new scheme (if applicable).
Note that "Padre::DB::Migrate" is quiet by default. And if your SQL statements are buggy, you will not see anything but the database not being updated. Therefore, to debug what's going on, add the "-DEBUG" flag to "Padre::DB::Migrate" call (add it as the last parameter):
```
        use Padre::DB::Migrate 0.01 {
            [...]
        }, '-DEBUG'
```

Congratulations! The database has been updated, and will be updated automatically when users will run the new Padre version...

Accessing and using the database

Now that the database has been updated, you can start using it. Each new table will have a "Padre::DB::YourTable" module created automatically at runtime by "ORLite", providing you with the standard methods described below (see METHODS).

Note: we prefer using underscore for table names instead of camel case. "ORLite" is smart enough to convert underscore names to camel case module names.

But what if you want to provide some particular methods? For example, one can imagine that if you create a table "accessed_files" retaining the path and the opening timestamp, you want to create a method "most_recent()" that will return the last opened file.

In that case, that's quite easy, too:

Create a standard "Padre::DB::YourTable" module where you will put your method. Note that all standard methods described above will still be available.
Don't forget to "use Padre::DB::YourTable" in "Padre::DB", so that other Padre modules will get access to all db tables by just using "Padre::DB".

METHODS

Those methods are automatically created for each of the tables (see above). Note that the modules automatically created provide both class methods and instance methods, where the object instances each represent a table record.

dsn

  my $string = Padre::DB->dsn;

The "dsn" accessor returns the DBI connection string used to connect to the SQLite database as a string.

dbh

  my $handle = Padre::DB->dbh;

To reliably prevent potential SQLite deadlocks resulting from multiple connections in a single process, each ORLite package will only ever maintain a single connection to the database.

During a transaction, this will be the same (cached) database handle.

Although in most situations you should not need a direct DBI connection handle, the "dbh" method provides a method for getting a direct connection in a way that is compatible with connection management in ORLite.

Please note that these connections should be short-lived, you should never hold onto a connection beyond your immediate scope.

The transaction system in ORLite is specifically designed so that code using the database should never have to know whether or not it is in a transation.

Because of this, you should never call the ->disconnect method on the database handles yourself, as the handle may be that of a currently running transaction.

Further, you should do your own transaction management on a handle provided by the <dbh> method.

In cases where there are extreme needs, and you absolutely have to violate these connection handling rules, you should create your own completely manual DBI->connect call to the database, using the connect string provided by the "dsn" method.

The "dbh" method returns a DBI::db object, or throws an exception on error.

begin

  Padre::DB->begin;

The "begin" method indicates the start of a transaction.

In the same way that ORLite allows only a single connection, likewise it allows only a single application-wide transaction.

No indication is given as to whether you are currently in a transaction or not, all code should be written neutrally so that it works either way or doesn't need to care.

Returns true or throws an exception on error.

commit

  Padre::DB->commit;

The "commit" method commits the current transaction. If called outside of a current transaction, it is accepted and treated as a null operation.

Once the commit has been completed, the database connection falls back into auto-commit state. If you wish to immediately start another transaction, you will need to issue a separate ->begin call.

Returns true or throws an exception on error.

rollback

The "rollback" method rolls back the current transaction. If called outside of a current transaction, it is accepted and treated as a null operation.

Once the rollback has been completed, the database connection falls back into auto-commit state. If you wish to immediately start another transaction, you will need to issue a separate ->begin call.

If a transaction exists at END-time as the process exits, it will be automatically rolled back.

Returns true or throws an exception on error.

do

  Padre::DB->do(
      'insert into table ( foo, bar ) values ( ?, ? )', {},
      \$foo_value,
      \$bar_value,
  );

The "do" method is a direct wrapper around the equivalent DBI method, but applied to the appropriate locally-provided connection or transaction.