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DBIx::SearchBuilder::Record - Perl extension for subclassing, so you can deal with a Record |
DBIx::SearchBuilder::Record - Perl extension for subclassing, so you can deal with a Record
module MyRecord; use DBIx::SearchBuilder::Record; @ISA = (DBIx::SearchBuilder::Record);
sub _Init {
my $self = shift;
my $DBIxHandle = shift; # A DBIx::SearchBuilder::Handle::foo object for your database
$self->_Handle($DBIxHandle);
$self->Table("Users");
}
# Tell Record what the primary keys are
sub _PrimaryKeys {
my $self = shift;
return['id'];
}
#Preferred and most efficient way to specify fields attributes in a derived #class, used by the autoloader to construct Attrib and SetAttrib methods.
# read: calling $Object->Foo will return the value of this record's Foo column # write: calling $Object->SetFoo with a single value will set Foo's value in # both the loaded object and the database
sub _ClassAccessible {
{
Tofu => { 'read'=>1, 'write'=>1 },
Maz => { 'auto'=>1, },
Roo => { 'read'=>1, 'auto'=>1, 'public'=>1, },
};
}
# specifying an _Accessible subroutine in a derived class is depriciated. # only '/' and ',' delimiters work, not full regexes
sub _Accessible {
my $self = shift;
my %Cols = (
id => 'read', # id is an immutable primary key
Username => 'read/write', #read/write.
Password => 'write', # password. write only. see sub IsPassword
Created => 'read' # A created date. read-only
);
return $self->SUPER::_Accessible(@_, %Cols);
}
# A subroutine to check a user's password without ever returning the current password #For security purposes, we didn't expose the Password method above
sub IsPassword {
my $self = shift;
my $try = shift;
# note two __s in __Value. Subclasses may muck with _Value, but they should
# never touch __Value
if ($try eq $self->__Value('Password')) {
return (1);
}
else {
return (undef);
}
}
# Override DBIx::SearchBuilder::Create to do some checking on create
sub Create {
my $self = shift;
my %fields = ( UserId => undef,
Password => 'default', #Set a default password
@_);
#Make sure a userid is specified
unless ($fields{'UserId'}) {
die "No userid specified.";
}
#Get DBIx::SearchBuilder::Record->Create to do the real work
return ($self->SUPER::Create( UserId => $fields{'UserId'},
Password => $fields{'Password'},
Created => time ));
}
DBIx::SearchBuilder::Record is designed to work with DBIx::SearchBuilder.
DBIx::SB::Record abstracts the agony of writing the common and generally simple SQL statements needed to serialize and De-serialize an object to the database. In a traditional system, you would define various methods on your object 'create', 'find', 'modify', and 'delete' being the most common. In each method you would have a SQL statement like:
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, DBIx::SearchBuilder::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. Its pretty simple, and incredibly powerful. For more complex cases, you can, gasp, do more complicated things by overriding certain methods. Lets stick with the simple case for now.
The two methods in question are '_Init' and '_ClassAccessible', all they really do are define some values and send you on your way. As you might have guessed the '_' suggests that these are private methods, they are. They will get called by your record objects constructor.
o. '_Init'
Defines what table we are talking about, and set a variable to store
the database handle.
o. '_ClassAccessible
Defines what operations may be performed on various data selected
from the database. For example you can define fields to be mutable,
or immutable, there are a few other options but I don't understand
what they do at this time.
And really, thats it. So lets have some sample code, but first the example code makes the following assumptions:
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)
[file:///example/Simple.pm]
000: package Simple; 001: use DBIx::SearchBuilder::Record; 002: @ISA = (DBIx::SearchBuilder::Record);
This should be pretty obvious, name the package, import ::Record and then define ourself as a subclass of ::Record.
003: 004: sub _Init { 005: my $this = shift; 006: my $handle = shift; 007: 008: $this->_Handle($handle); 009: $this->Table(``Simple''); 010: 011: return ($this); 012: }
Here we set our handle and table name, while its not obvious so far, we'll see later that $handle (line: 006) gets passed via ::Record::new when a new instance is created. Thats actually an important concept, the DB handle is not bound to a single object but rather, its shared across objects.
013: 014: sub _ClassAccessible { 015: { 016: Foo => { 'read' => 1 }, 017: Bar => { 'read' => 1, 'write' => 1 }, 018: Id => { 'read' => 1 } 019: }; 020: }
What's happening might be obvious, but just in case this method is going to return a reference to a hash. That hash is where our columns are defined, as well as what type of operations are acceptable.
021: 022: 1;
Its perl, duh.
Now, on to the code that will actually *do* something with this object.
[file://examples/ex.pl] 000: use DBIx::SearchBuilder::Handle; 001: use Simple;
Use two packages, the first is where I get the DB handle from, the latter is the object I just created.
002: 003: my $handle = DBIx::SearchBuilder::Handle->new(); 004: $handle->Connect( 'Driver' => 'Pg', 005: 'Database' => 'test', 006: 'Host' => 'reason', 007: 'User' => 'mhat', 008: 'Password' => '');
Creates a new DBIx::SB::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.
009: 010: my $s = new Simple($handle); 011: 012: $s->LoadById(1);
LoadById is one of four 'LoadBy' methods, as the name suggests it searches
for an row in the database that has id='0'. ::SearchBuilder has, what I
think is a bug, in that it current requires there to be an id field. More
reasonably it also assumes that the id field is unique. LoadById($id) will
do undefined things if there is >1 row with the same id.
In addition to LoadById, we also have:
o. LoadByCol
Takes two arguments, a column name and a value. Again, it will do
undefined things if you use non-unique things.
o. LoadByCols
Takes a hash of columns=>values and returns the *first* to match.
First is probably lossy across databases vendors.
o. LoadFromHash
Populates this record with data from a DBIx::SearchBuilder. I'm
currently assuming that DBIx::SearchBuilder 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 accessos and mutators for us, so all we need to do is call the methods. Accessors are named <Field>(), and Mutators are named Set<Field>($). On to the example, just appending this to the code from the last example.
013: 014: print ``ID : '', $s->Id(), ``\n''; 015: print ``Foo : '', $s->Foo(), ``\n''; 016: print ``Bar : '', $s->Bar(), ``\n'';
Thats all you have to to get the data, now to change the data!
017: 018: $s->SetBar('NewBar');
Pretty simple! Thats really all there is to it. Set<Field>($) 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.
019: my ($res, $str) = $s->SetId('2'); 020: if (! $res) { 021: ## Print the error! 022: print ``$str\n''; 023: }
The output will be: >> Immutable field
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 a 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 fields.
023: ## Get a new record object. 024: $s1 = new Simple($handle); 025: $s1->Create('Id' => 4, 026: 'Foo' => 'Foooooo', 027: 'Bar' => 'Barrrrr');
Poof! A new row in the database has been created! Now lets delete the object!
028: 029: $s1 = undef; 030: $s1 = new Simple($handle); 031: $s1->LoadById(4); 032: $s1->Delete();
And its gone.
For simple use, thats more or less all there is to it. The next part of this HowTo will discuss using container classes, overloading, and what ever else I think of.
Returns this row's primary key.
Matt Knopp owes docs for this function.
Preferred and most efficient way to specify fields attributes in a derived class.
sub _ClassAccessible {
{
Tofu => { 'read'=>1, 'write'=>1 },
Maz => { 'auto'=>1, },
Roo => { 'read'=>1, 'auto'=>1, 'public'=>1, },
};
}
Takes a field name and returns that field's value. Subclasses should never overrid __Value.
_Value takes a single column name and returns that column's value for this row. Subclasses can override _Value to insert custom access control.
_Set takes a single column name and a single unquoted value. It updates both the in-memory value of this column and the in-database copy. Subclasses can override _Set to insert custom access control.
Takes a single argument, $id. Calls LoadByRow to retrieve the row whose primary key is $id
Takes two arguments, a column and a value. The column can be any table column which contains unique values. Behavior when using a non-unique value is undefined
Takes a hash of columns and values. Loads the first record that matches all keys.
Loads a record by its primary key. TODO: BUG: Column name is currently hard coded to 'id'
Takes a hashref, such as created by DBIx::SearchBuilder and populates this record's loaded values hash.
Takes an array of key-value pairs and drops any keys that aren't known as columns for this recordtype
Returns or sets the name of the current Table
Returns or sets the current DBIx::SearchBuilder::Handle object
Takes no parameters and returns no arguments. This private routine iterates through $self->{'values'} and makes sure that all keys are lowercase.
Jesse Vincent, <jesse@fsck.com>
Enhancements by Ivan Kohler, <ivan-rt@420.am>
Docs by Matt Knopp <mhat@netlag.com>
perl(1).
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DBIx::SearchBuilder::Record - Perl extension for subclassing, so you can deal with a Record |