How to Model Ternary Relationship in CakePhp? - database

Question

Page table
(1)
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|
(*)
User_Moderate_Page (*)----------- (1)Access_level table
(*)
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(1)
User table
How do i Model such a ternary relationship in CakePhp?
User to Page can be modelled using the hasBelongtoMany Relationship. But User_Moderate_page is just an association table, should I even write a Model for User_Moderate_Page in Cake?

Answer 1

I'm not sure CakePHP accepts this, but what you should do is create the table with a primary key and the 3 foreign keys. Somewhat like this:
CREATE TABLE IF NOT EXISTS `mydb`.`access_levels_pages_users` (
`id` INT NOT NULL AUTO_INCREMENT ,
`page_id` INT NOT NULL ,
`access_level_id` INT NOT NULL ,
`user_id` INT NOT NULL ,
PRIMARY KEY (`id`) ,
INDEX `fk_access_levels_pages_users_pages` (`page_id` ASC) ,
INDEX `fk_access_levels_pages_users_access_levels1` (`access_level_id` ASC) ,
INDEX `fk_access_levels_pages_users_users1` (`user_id` ASC) ,
CONSTRAINT `fk_access_levels_pages_users_pages`
FOREIGN KEY (`page_id` )
REFERENCES `mydb`.`pages` (`id` )
ON DELETE NO ACTION
ON UPDATE NO ACTION,
CONSTRAINT `fk_access_levels_pages_users_access_levels1`
FOREIGN KEY (`access_level_id` )
REFERENCES `mydb`.`access_levels` (`id` )
ON DELETE NO ACTION
ON UPDATE NO ACTION,
CONSTRAINT `fk_access_levels_pages_users_users1`
FOREIGN KEY (`user_id` )
REFERENCES `mydb`.`users` (`id` )
ON DELETE NO ACTION
ON UPDATE NO ACTION)
ENGINE = InnoDB
Now, I'm not sure Cake will bake this table, so you might have to try and make the models by hand, this table would have belongsTo the 3 other tables. The other 3 tables non association tables will have to have a HMABTM relationship with the other 2, as in users HMABTM access_levels and pages and so on.
Again, not sure if it will work. I would suggest maybe trying to see if you can model it in a different manner.

Answer 2

Let me generalize it by describing it with generic tables:
Lets say you have 3 tables - firsts, seconds, thirds - each with primary keys 'id'.
let your join table be called 'firsts_seconds_thirds' with foreign keys to each main table:
first_id
second_id
third_id
<additional fields of this association table>
usually we define HABTM relationships between tables, in this case we need to create a cake model for the join table - lets call it FirstsSecondsThird (By cakePhp's naming conventions)
The relationship between models you need to define is:
First hasMany FirstsSecondsThird
Second hasMany FirstsSecondsThird
Third hasMany FirstsSecondsThird
FirstsSecondsThird belongsTo First,Second,Third
The need for this is explained here - Associations: Linking Models Together
Code for the same:
class First extends AppModel {
public $hasMany = array(
'FirstsSecondsThird' => array(
'className' => 'FirstsSecondsThird',
'foreignKey' => 'first_id'
)
);
}
//Same for classes 'Second' and 'Third'
class FirstsSecondsThird extends AppModel {
public $belongsTo = array(
'First' => array(
'className' => 'First',
'foreignKey' => 'first_id'
),
'Second' => array(
'className' => 'Second',
'foreignKey' => 'second_id'
),
'Third' => array(
'className' => 'Third',
'foreignKey' => 'third_id'
)
);
}
The models are perfectly setup, but now inserting/updating/deleting from the main/join table should be done correctly or they are of no use.
Model::saveMany() and Model::saveAssociated(), using the option 'deep' etc. need to be used. Read about it here. You also need to think about ON DELETE RESTRICT/CASCADE for these join tables and model them appropriately.

Answer 3

Look up ACL. It is complicated, but it is what you need (especially if you need the flexibility in setting up who can moderate what page)