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Morphed Relations

In some rare cases you might want to link your models to undefined target, use set of morphed relations and common interface for such purposes.

You are not able to pre-load morphed relations.

Belongs To Morphed

BELONGS_TO_MORPHED relation gives ability to assign model to various parents based on morph key value. Morphed relations can be declared exactly same way as BELONGS_TO, however you must link your relation to an interface rather than specific model.

Disclaimer: polymorphic relations must be used only when you absolutely sure about it, avoid using BELONGS_TO_MORPHED as much as you can.

Let's try to create new ORM entity Photo which we would like to assign to User or Post models: "create:record photo -f id:primary -f imageURL:string"

class Photo extends Record 
{
    const SCHEMA = [
        'id'       => 'primary',
        'imageURL' => 'string'
    ];
}

Before declaring our relation we would have to create an interface to link our model to:

interface PhotoHolderInterface
{

}

Now we can describe our relation in Photo model, since we want both Post and User get inverted relations we will declare INVERSE option.

protected $schema = [
    'id'       => 'primary',
    'imageURL' => 'string',
    'parent'   => [
        self::BELONGS_TO_MORPHED => PhotoHolderInterface::class,
        self::INVERSE    => [self::HAS_ONE, 'photo']
    ]
];

The only thing we have to do to let our User and Post model have photo - implement PhotoHolderInterface, inverse relation in this case will be created automatically.

class User extends Record implements PhotoHolderInterface
{
    ...

Now we can run schema update and check our "photos" table:

Columns of primary.photos:
+-------------+-------------------------+----------------+-----------+--------------------------------------------+
| Column:     | Database Type:          | Abstract Type: | PHP Type: | Default Value:                             |
+-------------+-------------------------+----------------+-----------+--------------------------------------------+
| id          | serial                  | primary        | int       | nextval('primary_photos_id_seq'::regclass) |
| imageURL    | character varying (255) | string         | string    | ---                                        |
| parent_type | character varying (32)  | string         | string    | ---                                        |
| parent_id   | integer                 | integer        | int       | ---                                        |
+-------------+-------------------------+----------------+-----------+--------------------------------------------+

Indexes of primary.photos:
+----------------------------------------------------------+-------+------------------------+
| Name:                                                    | Type: | Columns:               |
+----------------------------------------------------------+-------+------------------------+
| primary_photos_index_parent_type_parent_id_55f98f146672f | INDEX | parent_type, parent_id |
+----------------------------------------------------------+-------+------------------------+

As you can see relation created compound index using inner and morph keys "parent_id" and "parent_type". Both keys can be configured using relation options:

Option Default Description
OUTER_KEY {outer:primaryKey} By default, we are looking for primary key in our outer records, outer key must present in every outer record and be consistent (id).
INNER_KEY {name:singular}_{definition:outerKey} Inner key name will be created based on singular relation name and outer key namet (parent_id).
MORPH_KEY {name:singular}_type Morph key created based on singular relation name and postfix _type (parent_type).
CREATE_INDEXES true Relation allowed to create indexes in outer table.
NULLABLE true Nullable by default.

No foreign keys are created for BELONGS_TO_MORPHED relation.

WE can operate with our model same way as in case with BELONG_TO relation:

$photo = new Photo();
$photo->imageURL = 'some-url';
$photo->parent = User::findOne();
$photo->save();

//We can change parent to post at any moment
$post = Post::findOne();

$photo->parent = $post;
$photo->save();

dump($post->photo);

Simply declare HAS_MANY inversion to link multiple photos to morphed parent.

Many To Many Morphed

As in case with BELONGS_TO you are able to define polymorphic many to many connection. Let's try to do an example using model Tag. Again, to create our Tag model - "create:record tag -f id:primary -f name:string":

class Tag extends Record
{
    const SCHEMA = [
        'id'   => 'primary',
        'name' => 'string'
    ];
}

Now, we are going to link tag with TaggableInterface (empty) and implement such interface in User and Post models:

protected $schema = [
    'id'     => 'primary',
    'name'   => 'string',
    'tagged' => [
        self::MANY_TO_MORPHED => TaggableInterface::class,
        self::INVERSE      => 'tags'
    ]
];

As before, the best way to create relation from User and Post to Tags - use INVERSE option.

After updating ORM schema let's check pivot table, this time our table follow relation name (not as in previous case "role_user_map") so it named "tagged_map":

Columns of primary.tagged_map:
+-------------+------------------------+----------------+-----------+----------------+
| Column:     | Database Type:         | Abstract Type: | PHP Type: | Default Value: |
+-------------+------------------------+----------------+-----------+----------------+
| tag_id      | integer                | integer        | int       | ---            |
| tagged_type | character varying (32) | string         | string    | ---            |
| tagged_id   | integer                | integer        | int       | ---            |
+-------------+------------------------+----------------+-----------+----------------+

Indexes of primary.tagged_map:
+-----------------------------------------------+--------------+--------------------------------+
| Name:                                         | Type:        | Columns:                       |
+-----------------------------------------------+--------------+--------------------------------+
| primary_tagged_map_index_tag_id_55f9c032ee81f | INDEX        | tag_id                         |
| 6ec6a75196a6baf6b0c43f00b500c35b              | UNIQUE INDEX | tag_id, tagged_type, tagged_id |
+-----------------------------------------------+--------------+--------------------------------+

Foreign keys of primary.tagged_map:
+-------------------------------------------------+---------+----------------+-----------------+------------+------------+
| Name:                                           | Column: | Foreign Table: | Foreign Column: | On Delete: | On Update: |
+-------------------------------------------------+---------+----------------+-----------------+------------+------------+
| primary_tagged_map_foreign_tag_id_55f9c032edecc | tag_id  | primary_tags   | id              | CASCADE    | CASCADE    |
+-------------------------------------------------+---------+----------------+-----------------+------------+------------+

As in case with BELONGS_TO_MORPHED you can observe morphed key in our pivot table. To better understand how such table is created we can check relation options which are very similar to MANY_TO_MANY:

Option Default Description
MORPHED_ALIASES [] Association list between tables and roles, internal.
PIVOT_TABLE {name:singular}_map Pivot table name will be generated based on singular relation name and _map postfix (tagger_map).
INNER_KEY {record:primaryKey} Inner key of parent record will be used to fill "THOUGHT_INNER_KEY" in pivot table. (tag.id)
OUTER_KEY {outer:primaryKey} We are going to use primary key of outer table to fill "THOUGHT_OUTER_KEY" in pivot table. This is technically "inner" key of outer record, we will name it "outer key" for simplicity. (id)
MORPH_KEY {name:singular}_type Declares what specific record pivot record linking to (tagged_type).
THOUGHT_INNER_KEY {record:role}_{definition:innerKey} Linking pivot table and parent record (tag_id).
THOUGHT_OUTER_KEY {outer:role}_{definition:outerKey} Linking pivot table and outer records (tagged_id).
CONSTRAINT true Relations will set constraints in pivot table (foreign keys).
CONSTRAINT_ACTION CASCADE https://en.wikipedia.org/wiki/Foreign_key
CREATE_INDEXES true Relation is allowed to create indexes in pivot table
CREATE_PIVOT true Relation allowed to create pivot table.
PIVOT_COLUMNS [] Additional set of columns to be added into pivot table, you can use same column definition type as you using for your records.
PIVOT_DEFAULTS [] Set of default values to be used for pivot table columns.
WHERE_PIVOT [] Where statement in a form of simplified array definition to be applied to pivot table data.

To order models with our tag we have to use sup relation:

$tag = new Tag();
$tag->name = 'First';
$tag->save();

$tag->tagged->posts->link(User::findOne());
$tag->tagged->posts->link(Post::findOne());

$tag->save();

On another end we can assign tags to photos directly:

$photo->tags->link($tag);

To get access to tagged entities use sub relation as iterator:

$tag = Tag::findOne();

dump($tag->tagged->users);
dump($tag->tagged->posts);

Accessing Tags from User or Post models are identical to MANY_TO_MANY relation.