Associations: Linking Models Together

Associations: Linking Models Together

One of the most powerful features of CakePHP is the ability to link relational mapping provided by the model. In CakePHP, the links between models are handled through associations.
Defining relations between different objects in your application should be a natural process. For example: in a recipe database, a recipe may have many reviews, reviews have a single author, and authors may have many recipes. Defining the way these relations work allows you to access your data in an intuitive and powerful way.
The purpose of this section is to show you how to plan for, define, and utilize associations between models in CakePHP.
While data can come from a variety of sources, the most common form of storage in web applications is a relational database. Most of what this section covers will be in that context.
For information on associations with Plugin models, see Plugin Models.

Relationship Types

The four association types in CakePHP are: hasOne, hasMany, belongsTo, and hasAndBelongsToMany (HABTM).

Relationship	Association Type	Example
one to one	hasOne	A user has one profile.
one to many	hasMany	A user can have multiple recipes.
many to one	belongsTo	Many recipes belong to a user.
many to many	hasAndBelongsToMany	Recipes have, and belong to many ingredients.

Associations are defined by creating a class variable named after the association you are defining. The class variable can sometimes be as simple as a string, but can be as complete as a multidimensional array used to define association specifics.

class User extends AppModel {
    public $hasOne = 'Profile';
    public $hasMany = array(
        'Recipe' => array(
            'className' => 'Recipe',
            'conditions' => array('Recipe.approved' => '1'),
            'order' => 'Recipe.created DESC'
        )
    );
}

In the above example, the first instance of the word ‘Recipe’ is what is termed an ‘Alias’. This is an identifier for the relationship and can be anything you choose. Usually, you will choose the same name as the class that it references. However, aliases for each model must be unique app wide. For example it is appropriate to have:

class User extends AppModel {
    public $hasMany = array(
        'MyRecipe' => array(
            'className' => 'Recipe',
        )
    );
    public $hasAndBelongsToMany = array(
        'MemberOf' => array(
            'className' => 'Group',
        )
    );
}

class Group extends AppModel {
    public $hasMany = array(
        'MyRecipe' => array(
            'className' => 'Recipe',
        )
    );
    public $hasAndBelongsToMany = array(
        'Member' => array(
            'className' => 'User',
        )
    );
}

but the following will not work well in all circumstances:

class User extends AppModel {
    public $hasMany = array(
        'MyRecipe' => array(
            'className' => 'Recipe',
        )
    );
    public $hasAndBelongsToMany = array(
        'Member' => array(
            'className' => 'Group',
        )
    );
}

class Group extends AppModel {
    public $hasMany = array(
        'MyRecipe' => array(
            'className' => 'Recipe',
        )
    );
    public $hasAndBelongsToMany = array(
        'Member' => array(
            'className' => 'User',
        )
    );
}

because here we have the alias ‘Member’ referring to both the User (in Group) and the Group (in User) model in the HABTM associations. Choosing non-unique names for model aliases across models can cause unexpected behavior.
Cake will automatically create links between associated model objects. So for example in your User model you can access the Recipe model as:

$this->Recipe->someFunction();

Similarly in your controller you can access an associated model simply by following your model associations:

$this->User->Recipe->someFunction();

Note

Remember that associations are defined ‘one way’. If you define User hasMany Recipe that has no effect on the Recipe Model. You need to define Recipe belongsTo User to be able to access the User model from your Recipe model

hasOne

Let’s set up a User model with a hasOne relationship to a Profile model.
First, your database tables need to be keyed correctly. For a hasOne relationship to work, one table has to contain a foreign key that points to a record in the other. In this case the profiles table will contain a field called user_id. The basic pattern is:
hasOne: the other model contains the foreign key.

Relation	Schema
Apple hasOne Banana	bananas.apple_id
User hasOne Profile	profiles.user_id
Doctor hasOne Mentor	mentors.doctor_id

Note

It is not mandatory to follow CakePHP conventions, you can easily override the use of any foreignKey in your associations definitions. Nevertheless sticking to conventions will make your code less repetitive, easier to read and to maintain.

The User model file will be saved in /app/Model/User.php. To define the ‘User hasOne Profile’ association, add the $hasOne property to the model class. Remember to have a Profile model in /app/Model/Profile.php, or the association won’t work:

class User extends AppModel {
    public $hasOne = 'Profile';
}

There are two ways to describe this relationship in your model files. The simplest method is to set the $hasOne attribute to a string containing the classname of the associated model, as we’ve done above.
If you need more control, you can define your associations using array syntax. For example, you might want to limit the association to include only certain records.

class User extends AppModel {
    public $hasOne = array(
        'Profile' => array(
            'className' => 'Profile',
            'conditions' => array('Profile.published' => '1'),
            'dependent' => true
        )
    );
}

Possible keys for hasOne association arrays include:

• className: the classname of the model being associated to the current model. If you’re defining a ‘User hasOne Profile’ relationship, the className key should equal ‘Profile.’
• foreignKey: the name of the foreign key found in the other model. This is especially handy if you need to define multiple hasOne relationships. The default value for this key is the underscored, singular name of the current model, suffixed with ‘_id’. In the example above it would default to ‘user_id’.
• conditions: an array of find() compatible conditions or SQL strings such as array(‘Profile.approved’ => true)
• fields: A list of fields to be retrieved when the associated model data is fetched. Returns all fields by default.
• order: an array of find() compatible order clauses or SQL strings such as array(‘Profile.last_name’ => ‘ASC’)
• dependent: When the dependent key is set to true, and the model’s delete() method is called with the cascade parameter set to true, associated model records are also deleted. In this case we set it true so that deleting a User will also delete her associated Profile.

Once this association has been defined, find operations on the User model will also fetch a related Profile record if it exists:

//Sample results from a $this->User->find() call.

Array
(
    [User] => Array
        (
            [id] => 121
            [name] => Gwoo the Kungwoo
            [created] => 2007-05-01 10:31:01
        )
    [Profile] => Array
        (
            [id] => 12
            [user_id] => 121
            [skill] => Baking Cakes
            [created] => 2007-05-01 10:31:01
        )
)

belongsTo

Now that we have Profile data access from the User model, let’s define a belongsTo association in the Profile model in order to get access to related User data. The belongsTo association is a natural complement to the hasOne and hasMany associations: it allows us to see the data from the other direction.
When keying your database tables for a belongsTo relationship, follow this convention:
belongsTo: the current model contains the foreign key.

Relation	Schema
Banana belongsTo Apple	bananas.apple_id
Profile belongsTo User	profiles.user_id
Mentor belongsTo Doctor	mentors.doctor_id

Tip

If a model(table) contains a foreign key, it belongsTo the other model(table).

We can define the belongsTo association in our Profile model at /app/Model/Profile.php using the string syntax as follows:

class Profile extends AppModel {
    public $belongsTo = 'User';
}

We can also define a more specific relationship using array syntax:

class Profile extends AppModel {
    public $belongsTo = array(
        'User' => array(
            'className' => 'User',
            'foreignKey' => 'user_id'
        )
    );
}

Possible keys for belongsTo association arrays include:

• className: the classname of the model being associated to the current model. If you’re defining a ‘Profile belongsTo User’ relationship, the className key should equal ‘User.’
• foreignKey: the name of the foreign key found in the current model. This is especially handy if you need to define multiple belongsTo relationships. The default value for this key is the underscored, singular name of the other model, suffixed with _id.
• conditions: an array of find() compatible conditions or SQL strings such as array('User.active' => true)
• type: the type of the join to use in the SQL query, default is LEFT which may not fit your needs in all situations, INNER may be helpful when you want everything from your main and associated models or nothing at all! (effective when used with some conditions of course). (NB: type value is in lower case - i.e. left, inner)
• fields: A list of fields to be retrieved when the associated model data is fetched. Returns all fields by default.
• order: an array of find() compatible order clauses or SQL strings such as array('User.username' => 'ASC')
• counterCache: If set to true the associated Model will automatically increase or decrease the “[singular_model_name]_count” field in the foreign table whenever you do a save() or delete(). If it’s a string then it’s the field name to use. The value in the counter field represents the number of related rows. You can also specify multiple counter caches by defining an array, see Multiple counterCache
• counterScope: Optional conditions array to use for updating counter cache field.

Once this association has been defined, find operations on the Profile model will also fetch a related User record if it exists:

//Sample results from a $this->Profile->find() call.

Array
(
   [Profile] => Array
        (
            [id] => 12
            [user_id] => 121
            [skill] => Baking Cakes
            [created] => 2007-05-01 10:31:01
        )
    [User] => Array
        (
            [id] => 121
            [name] => Gwoo the Kungwoo
            [created] => 2007-05-01 10:31:01
        )
)

hasMany

Next step: defining a “User hasMany Comment” association. A hasMany association will allow us to fetch a user’s comments when we fetch a User record.
When keying your database tables for a hasMany relationship, follow this convention:
hasMany: the other model contains the foreign key.

Relation	Schema
User hasMany Comment	Comment.user_id
Cake hasMany Virtue	Virtue.cake_id
Product hasMany Option	Option.product_id

We can define the hasMany association in our User model at /app/Model/User.php using the string syntax as follows:

class User extends AppModel {
    public $hasMany = 'Comment';
}

We can also define a more specific relationship using array syntax:

class User extends AppModel {
    public $hasMany = array(
        'Comment' => array(
            'className' => 'Comment',
            'foreignKey' => 'user_id',
            'conditions' => array('Comment.status' => '1'),
            'order' => 'Comment.created DESC',
            'limit' => '5',
            'dependent' => true
        )
    );
}

Possible keys for hasMany association arrays include:

• className: the classname of the model being associated to the current model. If you’re defining a ‘User hasMany Comment’ relationship, the className key should equal ‘Comment.’
• foreignKey: the name of the foreign key found in the other model. This is especially handy if you need to define multiple hasMany relationships. The default value for this key is the underscored, singular name of the actual model, suffixed with ‘_id’.
• conditions: an array of find() compatible conditions or SQL strings such as array(‘Comment.visible’ => true)
• order: an array of find() compatible order clauses or SQL strings such as array(‘Profile.last_name’ => ‘ASC’)
• limit: The maximum number of associated rows you want returned.
• offset: The number of associated rows to skip over (given the current conditions and order) before fetching and associating.
• dependent: When dependent is set to true, recursive model deletion is possible. In this example, Comment records will be deleted when their associated User record has been deleted.
• exclusive: When exclusive is set to true, recursive model deletion does the delete with a deleteAll() call, instead of deleting each entity separately. This greatly improves performance, but may not be ideal for all circumstances.
• finderQuery: A complete SQL query CakePHP can use to fetch associated model records. This should be used in situations that require very custom results. If a query you’re building requires a reference to the associated model ID, use the special {$__cakeID__$} marker in the query. For example, if your Apple model hasMany Orange, the query should look something like this: SELECT Orange.* from oranges as Orange WHERE Orange.apple_id = {$__cakeID__$};

Once this association has been defined, find operations on the User model will also fetch related Comment records if they exist:

//Sample results from a $this->User->find() call.

Array
(
    [User] => Array
        (
            [id] => 121
            [name] => Gwoo the Kungwoo
            [created] => 2007-05-01 10:31:01
        )
    [Comment] => Array
        (
            [0] => Array
                (
                    [id] => 123
                    [user_id] => 121
                    [title] => On Gwoo the Kungwoo
                    [body] => The Kungwooness is not so Gwooish
                    [created] => 2006-05-01 10:31:01
                )
            [1] => Array
                (
                    [id] => 124
                    [user_id] => 121
                    [title] => More on Gwoo
                    [body] => But what of the ‘Nut?
                    [created] => 2006-05-01 10:41:01
                )
        )
)

One thing to remember is that you’ll need a complimentary Comment belongsTo User association in order to get the data from both directions. What we’ve outlined in this section empowers you to get Comment data from the User. Adding the Comment belongsTo User association in the Comment model empowers you to get User data from the Comment model - completing the connection and allowing the flow of information from either model’s perspective.

counterCache - Cache your count()

This function helps you cache the count of related data. Instead of counting the records manually via find('count'), the model itself tracks any addition/deleting towards the associated $hasMany model and increases/decreases a dedicated integer field within the parent model table.
The name of the field consists of the singular model name followed by a underscore and the word “count”:

my_model_count

Let’s say you have a model called ImageComment and a model called Image, you would add a new INT-field to the images table and name it image_comment_count.
Here are some more examples:

Model	Associated Model	Example
User	Image	users.image_count
Image	ImageComment	images.image_comment_count
BlogEntry	BlogEntryComment	blog_entries.blog_entry_comment_count

Once you have added the counter field you are good to go. Activate counter-cache in your association by adding a counterCache key and set the value to true:

class ImageComment extends AppModel {
    public $belongsTo = array(
        'Image' => array(
            'counterCache' => true,
        )
    );
}

From now on, every time you add or remove a ImageComment associated to Image, the number within image_comment_count is adjusted automatically.

counterScope

You can also specify counterScope. It allows you to specify a simple condition which tells the model when to update (or when not to, depending on how you look at it) the counter value.
Using our Image model example, we can specify it like so:

class ImageComment extends AppModel {
    public $belongsTo = array(
        'Image' => array(
            'counterCache' => true,
            'counterScope' => array('Image.active' => 1) // only count if "Image" is active = 1
        )
    );
}

Multiple counterCache

Since 2.0 CakePHP supports having multiple counterCache in a single model relation. It is also possible to define a counterScope for each counterCache. Assuming you have a User model and a Message model and you want to be able to count the amount of read and unread messages for each user.

Model	Field	Description
User	users.messages_read	Count read Message
User	users.messages_unread	Count unread Message
Message	messages.is_read	Determines if a Message is read or not.

With this setup your belongsTo would look like this:

class Message extends AppModel {
    public $belongsTo = array(
        'User' => array(
            'counterCache' => array(
                'messages_read' => array('Message.is_read' => 1),
                'messages_unread' => array('Message.is_read' => 0)
            )
        )
    );
}

hasAndBelongsToMany (HABTM)

Alright. At this point, you can already call yourself a CakePHP model associations professional. You’re already well versed in the three associations that take up the bulk of object relations.
Let’s tackle the final relationship type: hasAndBelongsToMany, or HABTM. This association is used when you have two models that need to be joined up, repeatedly, many times, in many different ways.
The main difference between hasMany and HABTM is that a link between models in HABTM is not exclusive. For example, we’re about to join up our Recipe model with an Ingredient model using HABTM. Using tomatoes as an Ingredient for my grandma’s spaghetti recipe doesn’t “use up” the ingredient. I can also use it for a salad Recipe.
Links between hasMany associated objects are exclusive. If my User hasMany Comments, a comment is only linked to a specific user. It’s no longer up for grabs.
Moving on. We’ll need to set up an extra table in the database to handle HABTM associations. This new join table’s name needs to include the names of both models involved, in alphabetical order, and separated with an underscore ( _ ). The contents of the table should be two fields, each foreign keys (which should be integers) pointing to both of the primary keys of the involved models. To avoid any issues - don’t define a combined primary key for these two fields, if your application requires it you can define a unique index. If you plan to add any extra information to this table, or use a ‘with’ model, you should add an additional primary key field (by convention ‘id’).
HABTM requires a separate join table that includes both model names.

Relationship	HABTM Table Fields
Recipe HABTM Ingredient	ingredients_recipes.id, ingredients_recipes.ingredient_id, ingredients_recipes.recipe_id
Cake HABTM Fan	cakes_fans.id, cakes_fans.cake_id, cakes_fans.fan_id
Foo HABTM Bar	bars_foos.id, bars_foos.foo_id, bars_foos.bar_id

Note

Table names are by convention in alphabetical order. It is possible to define a custom table name in association definition

Make sure primary keys in tables cakes and recipes have “id” fields as assumed by convention. If they’re different than assumed, it has to be changed in model’s primaryKey
Once this new table has been created, we can define the HABTM association in the model files. We’re gonna skip straight to the array syntax this time:

class Recipe extends AppModel {
    public $hasAndBelongsToMany = array(
        'Ingredient' =>
            array(
                'className' => 'Ingredient',
                'joinTable' => 'ingredients_recipes',
                'foreignKey' => 'recipe_id',
                'associationForeignKey' => 'ingredient_id',
                'unique' => true,
                'conditions' => '',
                'fields' => '',
                'order' => '',
                'limit' => '',
                'offset' => '',
                'finderQuery' => '',
                'deleteQuery' => '',
                'insertQuery' => '',
                'with' => ''
            )
    );
}

Possible keys for HABTM association arrays include:

• className: the classname of the model being associated to the current model. If you’re defining a ‘Recipe HABTM Ingredient’ relationship, the className key should equal ‘Ingredient.’
• joinTable: The name of the join table used in this association (if the current table doesn’t adhere to the naming convention for HABTM join tables).
• with: Defines the name of the model for the join table. By default CakePHP will auto-create a model for you. Using the example above it would be called IngredientsRecipe. By using this key you can override this default name. The join table model can be used just like any “regular” model to access the join table directly. By creating a model class with such name and filename you can add any custom behavior to the join table searches, such as adding more information/columns to it
• foreignKey: the name of the foreign key found in the current model. This is especially handy if you need to define multiple HABTM relationships. The default value for this key is the underscored, singular name of the current model, suffixed with ‘_id’.
• associationForeignKey: the name of the foreign key found in the other model. This is especially handy if you need to define multiple HABTM relationships. The default value for this key is the underscored, singular name of the other model, suffixed with ‘_id’.

• unique: boolean or string keepExisting.

  • If true (default value) cake will first delete existing relationship records in the foreign keys table before inserting new ones. Existing associations need to be passed again when updating.
  • When false, cake will insert the relationship record, and that no join records are deleted during a save operation.
  • When set to keepExisting, the behavior is similar to true, but existing associations are not deleted.

• conditions: an array of find() compatible conditions or SQL string. If you have conditions on an associated table, you should use a ‘with’ model, and define the necessary belongsTo associations on it.
• fields: A list of fields to be retrieved when the associated model data is fetched. Returns all fields by default.
• order: an array of find() compatible order clauses or SQL strings
• limit: The maximum number of associated rows you want returned.
• offset: The number of associated rows to skip over (given the current conditions and order) before fetching and associating.
• finderQuery, deleteQuery, insertQuery: A complete SQL query CakePHP can use to fetch, delete, or create new associated model records. This should be used in situations that require very custom results.

Once this association has been defined, find operations on the Recipe model will also fetch related Tag records if they exist:

// Sample results from a $this->Recipe->find() call.

Array
(
    [Recipe] => Array
        (
            [id] => 2745
            [name] => Chocolate Frosted Sugar Bombs
            [created] => 2007-05-01 10:31:01
            [user_id] => 2346
        )
    [Ingredient] => Array
        (
            [0] => Array
                (
                    [id] => 123
                    [name] => Chocolate
                )
           [1] => Array
                (
                    [id] => 124
                    [name] => Sugar
                )
           [2] => Array
                (
                    [id] => 125
                    [name] => Bombs
                )
        )
)

Remember to define a HABTM association in the Ingredient model if you’d like to fetch Recipe data when using the Ingredient model.

Note

HABTM data is treated like a complete set, each time a new data association is added the complete set of associated rows in database is dropped and created again so you will always need to pass the whole data set for saving. For an alternative to using HABTM see hasMany through (The Join Model)

Tip

For more information on saving HABTM objects see Saving Related Model Data (HABTM)

hasMany through (The Join Model)

It is sometimes desirable to store additional data with a many to many association. Consider the following
Student hasAndBelongsToMany Course
Course hasAndBelongsToMany Student
In other words, a Student can take many Courses and a Course can be taken by many Students. This is a simple many to many association demanding a table such as this:

id | student_id | course_id

Now what if we want to store the number of days that were attended by the student on the course and their final grade? The table we’d want would be:

id | student_id | course_id | days_attended | grade

The trouble is, hasAndBelongsToMany will not support this type of scenario because when hasAndBelongsToMany associations are saved, the association is deleted first. You would lose the extra data in the columns as it is not replaced in the new insert.

Changed in version 2.1.

You can set unique setting to keepExisting circumvent losing extra data during the save operation. See unique key in HABTM association arrays.

The way to implement our requirement is to use a join model, otherwise known as a hasMany through association. That is, the association is a model itself. So, we can create a new model CourseMembership. Take a look at the following models.:

// Student.php
class Student extends AppModel {
    public $hasMany = array(
        'CourseMembership'
    );
}

// Course.php

class Course extends AppModel {
    public $hasMany = array(
        'CourseMembership'
    );
}

// CourseMembership.php

class CourseMembership extends AppModel {
    public $belongsTo = array(
        'Student', 'Course'
    );
}

The CourseMembership join model uniquely identifies a given Student’s participation on a Course in addition to extra meta-information.
Join models are pretty useful things to be able to use and Cake makes it easy to do so with its built-in hasMany and belongsTo associations and saveAll feature.

Creating and Destroying Associations on the Fly

Sometimes it becomes necessary to create and destroy model associations on the fly. This may be for any number of reasons:

• You want to reduce the amount of associated data fetched, but all your associations are on the first level of recursion.
• You want to change the way an association is defined in order to sort or filter associated data.

This association creation and destruction is done using the CakePHP model bindModel() and unbindModel() methods. (There is also a very helpful behavior called “Containable”, please refer to manual section about Built-in behaviors for more information). Let’s set up a few models so we can see how bindModel() and unbindModel() work. We’ll start with two models:

class Leader extends AppModel {
    public $hasMany = array(
        'Follower' => array(
            'className' => 'Follower',
            'order' => 'Follower.rank'
        )
    );
}

class Follower extends AppModel {
    public $name = 'Follower';
}

Now, in the LeadersController, we can use the find() method in the Leader model to fetch a Leader and its associated followers. As you can see above, the association array in the Leader model defines a “Leader hasMany Followers” relationship. For demonstration purposes, let’s use unbindModel() to remove that association in a controller action:

public function some_action() {
    // This fetches Leaders, and their associated Followers
    $this->Leader->find('all');

    // Let's remove the hasMany...
    $this->Leader->unbindModel(
        array('hasMany' => array('Follower'))
    );

    // Now using a find function will return
    // Leaders, with no Followers
    $this->Leader->find('all');

    // NOTE: unbindModel only affects the very next
    // find function. An additional find call will use
    // the configured association information.

    // We've already used find('all') after unbindModel(),
    // so this will fetch Leaders with associated
    // Followers once again...
    $this->Leader->find('all');
}

Note

Removing or adding associations using bind- and unbindModel() only works for the next find operation only unless the second parameter has been set to false. If the second parameter has been set to false, the bind remains in place for the remainder of the request.

Here’s the basic usage pattern for unbindModel():

$this->Model->unbindModel(
    array('associationType' => array('associatedModelClassName'))
);

Now that we’ve successfully removed an association on the fly, let’s add one. Our as-of-yet unprincipled Leader needs some associated Principles. The model file for our Principle model is bare, except for the public $name statement. Let’s associate some Principles to our Leader on the fly (but remember–only for just the following find operation). This function appears in the LeadersController:

public function another_action() {
    // There is no Leader hasMany Principles in
    // the leader.php model file, so a find here,
    // only fetches Leaders.
    $this->Leader->find('all');

    // Let's use bindModel() to add a new association
    // to the Leader model:
    $this->Leader->bindModel(
        array('hasMany' => array(
                'Principle' => array(
                    'className' => 'Principle'
                )
            )
        )
    );

    // Now that we're associated correctly,
    // we can use a single find function to fetch
    // Leaders with their associated principles:
    $this->Leader->find('all');
}

There you have it. The basic usage for bindModel() is the encapsulation of a normal association array inside an array whose key is named after the type of association you are trying to create:

$this->Model->bindModel(
    array('associationName' => array(
            'associatedModelClassName' => array(
                // normal association keys go here...
            )
        )
    )
);

Even though the newly bound model doesn’t need any sort of association definition in its model file, it will still need to be correctly keyed in order for the new association to work properly.

Multiple relations to the same model

There are cases where a Model has more than one relation to another Model. For example you might have a Message model that has two relations to the User model. One relation to the user that sends a message, and a second to the user that receives the message. The messages table will have a field user_id, but also a field recipient_id. Now your Message model can look something like:

class Message extends AppModel {
    public $belongsTo = array(
        'Sender' => array(
            'className' => 'User',
            'foreignKey' => 'user_id'
        ),
        'Recipient' => array(
            'className' => 'User',
            'foreignKey' => 'recipient_id'
        )
    );
}

Recipient is an alias for the User model. Now let’s see what the User model would look like:

class User extends AppModel {
    public $hasMany = array(
        'MessageSent' => array(
            'className' => 'Message',
            'foreignKey' => 'user_id'
        ),
        'MessageReceived' => array(
            'className' => 'Message',
            'foreignKey' => 'recipient_id'
        )
    );
}

It is also possible to create self associations as shown below:

class Post extends AppModel {

    public $belongsTo = array(
        'Parent' => array(
            'className' => 'Post',
            'foreignKey' => 'parent_id'
        )
    );

    public $hasMany = array(
        'Children' => array(
            'className' => 'Post',
            'foreignKey' => 'parent_id'
        )
    );
}

Fetching a nested array of associated records:
If your table has parent_id field you can also use find(‘threaded’) to fetch nested array of records using a single query without setting up any associations.

Joining tables

In SQL you can combine related tables using the JOIN statement. This allows you to perform complex searches across multiples tables (i.e: search posts given several tags).
In CakePHP some associations (belongsTo and hasOne) performs automatic joins to retrieve data, so you can issue queries to retrieve models based on data in the related one.
But this is not the case with hasMany and hasAndBelongsToMany associations. Here is where forcing joins comes to the rescue. You only have to define the necessary joins to combine tables and get the desired results for your query.

Note

Remember you need to set the recursion to -1 for this to work. I.e: $this->Channel->recursive = -1;

To force a join between tables you need to use the “modern” syntax for Model::find(), adding a ‘joins’ key to the $options array. For example:

$options['joins'] = array(
    array('table' => 'channels',
        'alias' => 'Channel',
        'type' => 'LEFT',
        'conditions' => array(
            'Channel.id = Item.channel_id',
        )
    )
);

$Item->find('all', $options);

Note

Note that the ‘join’ arrays are not keyed.

In the above example, a model called Item is left joined to the channels table. You can alias the table with the Model name, so the retrieved data complies with the CakePHP data structure.
The keys that define the join are the following:

• table: The table for the join.
• alias: An alias to the table. The name of the model associated with the table is the best bet.
• type: The type of join: inner, left or right.
• conditions: The conditions to perform the join.

With joins, you could add conditions based on Related model fields:

$options['joins'] = array(
    array('table' => 'channels',
        'alias' => 'Channel',
        'type' => 'LEFT',
        'conditions' => array(
            'Channel.id = Item.channel_id',
        )
    )
);

$options['conditions'] = array(
    'Channel.private' => 1
);

$privateItems = $Item->find('all', $options);

You could perform several joins as needed in hasAndBelongsToMany:
Suppose a Book hasAndBelongsToMany Tag association. This relation uses a books_tags table as join table, so you need to join the books table to the books_tags table, and this with the tags table:

$options['joins'] = array(
    array('table' => 'books_tags',
        'alias' => 'BooksTag',
        'type' => 'inner',
        'conditions' => array(
            'Books.id = BooksTag.books_id'
        )
    ),
    array('table' => 'tags',
        'alias' => 'Tag',
        'type' => 'inner',
        'conditions' => array(
            'BooksTag.tag_id = Tag.id'
        )
    )
);

$options['conditions'] = array(
    'Tag.tag' => 'Novel'
);

$books = $Book->find('all', $options);

Using joins allows you to have a maximum flexibility in how CakePHP handles associations and fetch the data, however in most cases you can use other tools to achieve the same results such as correctly defining associations, binding models on the fly and using the Containable behavior. This feature should be used with care because it could lead, in a few cases, into bad formed SQL queries if combined with any of the former techniques described for associating models.