Purpose

  select * from table where value='blah';

If you wanted to control what data a user could modify, you would have to do some special magic to make accessors do the right thing. Etc. The problem with this approach is that in a majority of the cases, the SQL is incredibly simple and the code from one method/object to the next was basically the same.

<trumpets>

Enter, Jifty::DBI::Record.

With ::Record, you can in the simple case, remove all of that code and replace it by defining two methods and inheriting some code. It's pretty simple and incredibly powerful. For more complex cases, you can do more complicated things by overriding certain methods. Let's stick with the simple case for now.

An Annotated Example

• The database is 'postgres',
• The host is 'reason',
• The login name is 'mhat',
• The database is called 'example',
• The table is called 'simple',
• The table looks like so:

        id     integer     not NULL,   primary_key(id),
        foo    varchar(10),
        bar    varchar(10)
      

First, let's define our record class in a new module named "Simple.pm".

  use warnings;
  use strict;

  package Simple;
  use Jifty::DBI::Schema;
  use Jifty::DBI::Record schema {
    column foo => type is 'text';
    column bar => type is 'text';
  };

  # your custom code goes here.

  1;

Like all perl modules, this needs to end with a true value.

Now, on to the code that will actually *do* something with this object. This code would be placed in your Perl script.

  use Jifty::DBI::Handle;
  use Simple;

Use two packages, the first is where I get the DB handle from, the latter is the object I just created.

  my $handle = Jifty::DBI::Handle->new();
  $handle->connect(
      driver   => 'Pg',
      database => 'test',
      host     => 'reason',
      user     => 'mhat',
      password => ''
  );

Creates a new Jifty::DBI::Handle, and then connects to the database using that handle. Pretty straight forward, the password '' is what I use when there is no password. I could probably leave it blank, but I find it to be more clear to define it.

 my $s = Simple->new( handle => $handle );

 $s->load_by_cols(id=>1);

load_by_cols

Takes a hash of column => value pairs and returns the *first* to match. First is probably lossy across databases vendors.

load_from_hash

Populates this record with data from a Jifty::DBI::Collection. I'm currently assuming that Jifty::DBI is what we use in cases where we expect > 1 record. More on this later.

Now that we have a populated object, we should do something with it! ::Record automagically generates accessors and mutators for us, so all we need to do is call the methods. accessors are named "column"(), and Mutators are named "set_column"($). On to the example, just appending this to the code from the last example.

 print "ID  : ", $s->id(),  "\n";
 print "Foo : ", $s->foo(), "\n";
 print "Bar : ", $s->bar(), "\n";

That's all you have to to get the data, now to change the data!

 $s->set_bar('NewBar');

Pretty simple! That's really all there is to it. Set<Field>($) returns a boolean and a string describing the problem. Lets look at an example of what will happen if we try to set a 'Id' which we previously defined as read only.

 my ($res, $str) = $s->set_id('2');
 if (! $res) {
   ## Print the error!
   print "$str\n";
 }

The output will be:

  >> Immutable column

Currently Set<Field> updates the data in the database as soon as you call it. In the future I hope to extend ::Record to better support transactional operations, such that updates will only happen when "you" say so.

Finally, adding and removing records from the database. ::Record provides a Create method which simply takes a hash of key => value pairs. The keys exactly map to database columns.

 ## Get a new record object.
 $s1 = Simple->new( handle => $handle );
 my ($id, $status_msg) = $s1->create(id  => 4,
                   foo => 'Foooooo', 
                   bar => 'Barrrrr');

Poof! A new row in the database has been created! Now lets delete the object!

 my $s2 = Simple->new( handle => $handle );
 $s2->load_by_cols(id=>4);
 $s2->delete();

And it's gone.

For simple use, that's more or less all there is to it. In the future, I hope to expand this how-to to discuss using container classes, overloading, and what ever else I think of.