DBIx::SearchBuilder::RUserdContributed Perl DocuDBIx::SearchBuilder::Record(3)NAMEDBIx::SearchBuilder::Record - Superclass for records loaded by
SearchBuilder
SYNOPSIS
package MyRecord;
use base qw/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 {
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, },
};
}
# A subroutine to check a user's password without returning the current value
# 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
)
);
}
DESCRIPTIONDBIx::SearchBuilder::Record is designed to work with
DBIx::SearchBuilder.
What is it trying to do.
DBIx::SearchBuilder::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.
'_Init'
Defines what table we are talking about, and set a variable to
store the database handle.
'_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.
An Annotated Example
The example code below 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)
First, let's define our record class in a new module named "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;
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.
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::SearchBuilder::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 $s = Simple->new($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:
LoadByCol
Takes two arguments, a column name and a value. Again, it will do
undefined things if you use non-unique things.
LoadByCols
Takes a hash of columns=>values and returns the *first* to match.
First is probably lossy across databases vendors.
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: $s1 = Simple->new($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: $s1 = Simple->new($handle);
031: $s1->LoadById(4);
032: $s1->Delete();
And its gone.
For simple use, thats more or less all there is to it. In the future,
I hope to exapand this HowTo to discuss using container classes,
overloading, and what ever else I think of.
METHOD NAMING
Each method has a lower case alias; '_' is used to separate words. For
example, the method "_PrimaryKeys" has the alias "_primary_keys".
METHODS
new
Instantiate a new record object.
id
Returns this row's primary key.
primary_keys
PrimaryKeys
Return a hash of the values of our primary keys for this function.
_Accessible KEY MODE
Private method.
Returns undef unless "KEY" is accessible in "MODE" otherwise returns
"MODE" value
_PrimaryKeys
Return our primary keys. (Subclasses should override this, but our
default is that we have one primary key, named 'id'.)
_ClassAccessible
An older way to specify fields attributes in a derived class. (The
current preferred method is by overriding "Schema"; if you do this and
don't override "_ClassAccessible", the module will generate an
appropriate "_ClassAccessible" based on your "Schema".)
Here's an example declaration:
sub _ClassAccessible {
{
Tofu => { 'read'=>1, 'write'=>1 },
Maz => { 'auto'=>1, },
Roo => { 'read'=>1, 'auto'=>1, 'public'=>1, },
};
}
ReadableAttributes
Returns an array of the attributes of this class defined as "read" => 1
in this class' _ClassAccessible datastructure
WritableAttributes
Returns an array of the attributes of this class defined as "write" =>
1 in this class' _ClassAccessible datastructure
__Value
Takes a field name and returns that field's value. Subclasses should
never override __Value.
_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
_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.
_Canonicalize PARAMHASH
This routine massages an input value (VALUE) for FIELD into something
that's going to be acceptable.
Takes
FIELD
VALUE
FUNCTION
Takes:
FIELD
VALUE
FUNCTION
Returns a replacement VALUE.
_Validate FIELD VALUE
Validate that VALUE will be an acceptable value for FIELD.
Currently, this routine does nothing whatsoever.
If it succeeds (which is always the case right now), returns true.
Otherwise returns false.
TruncateValue KEY VALUE
Truncate a value that's about to be set so that it will fit inside the
database' s idea of how big the column is.
(Actually, it looks at SearchBuilder's concept of the database, not
directly into the db).
_Object
_Object takes a single column name and an array reference. It creates
new object instance of class specified in _ClassAccessable structure
and calls LoadById on recently created object with the current column
value as argument. It uses the array reference as the object
constructor's arguments. Subclasses can override _Object to insert
custom access control or define default contructor arguments.
Note that if you are using a "Schema" with a "REFERENCES" field, this
is unnecessary: the method to access the column's value will
automatically turn it into the appropriate object.
Load
Takes a single argument, $id. Calls LoadById to retrieve the row whose
primary key is $id
LoadByCol
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
LoadByCols
Takes a hash of columns and values. Loads the first record that matches
all keys.
The hash's keys are the columns to look at.
The hash's values are either: scalar values to look for OR has
references which contain 'operator' and 'value'
LoadById
Loads a record by its primary key. Your record class must define a
single primary key column.
LoadByPrimaryKeys
Like LoadById with basic support for compound primary keys.
LoadFromHash
Takes a hashref, such as created by DBIx::SearchBuilder and populates
this record's loaded values hash.
_LoadFromSQL QUERYSTRING @BIND_VALUES
Load a record as the result of an SQL statement
Create
Takes an array of key-value pairs and drops any keys that aren't known
as columns for this recordtype
Delete
Delete this record from the database. On failure return a
Class::ReturnValue with the error. On success, return 1;
Table
Returns or sets the name of the current Table
_Handle
Returns or sets the current DBIx::SearchBuilder::Handle object
AUTHOR
Jesse Vincent, <jesse@fsck.com>
Enhancements by Ivan Kohler, <ivan-rt@420.am>
Docs by Matt Knopp <mhat@netlag.com>
SEE ALSO
DBIx::SearchBuilder
perl v5.14.2 2012-09-10 DBIx::SearchBuilder::Record(3)
