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Can we make a "Class Level Relationship" in Laravel, as opposed to an "Object Level Relationship"? – SEO

Consider the following scenario:

There are couple of entities in my Laravel application like the following:

  • Post
  • Page
  • Image
  • Video

All the above entities can have CustomFieldValues, which is another entity. The structure of the custom_field_values table is as follows:

  • ID
  • entity_id
  • custom_field_definition_id
  • value
  • [Timestamp fields]

All the CustomFieldValues belong to a single CustomFieldDefinition entity. Its table custom_field_definitions looks like following:

  • ID
  • parent_entity_name
  • definition_name
  • [Timestamp fields]

Following are some sample data from the custom_field_definitions table:

| ID | parent_entity_name | definition_name   |
|----|--------------------|-------------------|
| 1  | Post               | AuthorTwitterUrl  |
| 2  | Page               | SeoTitle          |
| 3  | Image              | OriginalSourceUrl |
| 4  | Video              | MpaaRating        |

As you can see, CustomFieldDefinitions are definitions of extra data, that we can store about each type of entity.

Following are some sampel data from the custom_field_values table:

| ID | entity_id | custom_field_definition_id | value                             |
|----|-----------|----------------------------|-----------------------------------|
| 1  | 1         | 1                          | https://twitter.com/StackOverflow |
| 2  | 1         | 2                          | My Page's SEO Title               |
| 3  | 1         | 3                          | http://example.com/image.jpg      |
| 4  | 1         | 4                          | G – General Audiences             |

A little description about the data contained in the custom_field_values table:

  • CustomFieldValue:1: The value for CustomFieldDefinition:1 and its entity 1 (Post:1, in this case, because CustomFieldDefinition:1 is related to Post.) is “https://twitter.com/StackOverflow“.
  • CustomFieldValue:2: The value for CustomFieldDefinition:2 and its entity 1 (Page:1, in this case, because CustomFieldDefinition:2 is related to Page.) is “My Page’s SEO Title”.
  • CustomFieldValue:3: The value for CustomFieldDefinition:3 and its entity 1 (Image:1, in this case, because CustomFieldDefinition:3 is related to Image.) is “http://example.com/image.jpg“.
  • CustomFieldValue:4: The value for CustomFieldDefinition:4 and its entity 1 (Video:1, in this case, because CustomFieldDefinition:4 is related to Video.) is “G – General Audiences”.

custom_field_values table’s entity_id can refer to any entity class, therefore it is not a foreign key in the DB level. Only in combination with custom_field_definition_id we can find to which entity it actually refers to.

Now, all is well and good, until I need to add a relationship called customFieldDefinitions to any of the entities (Say Post.).

class Post extends Model {
 public function customFieldDefinitions(){
  $this -> hasMany ('CustomFieldDefinition');
 }
}

The above does not work, because the datapoint that indicates the CustomFieldDefinition‘s relationship is not a foreign key field in the custom_field_definitions table, named post_id. We have to somehow build the relationship based on the fact that some records in the custom_field_definitions table has “Post” as the value of the field parent_entity_name.

CustomFieldDefinition::where('parent_entity_name', '=', 'Post');

The above snippet fetches the CustomFieldDefinitions that are related to the Post, however, it is not possible to do something like the following with the relationship:

class Post extends Model {
 public function customFieldDefinitions(){
  $this
   -> hasMany ('CustomFieldDefinition')
   -> where ('parent_entity_name', '=', 'Post')
  ;
 }
}

The where constraint works. But Laravel also injects the ID of the current Post object into the set of constraints.

So, what I want to do is, not consider the current object’s ID at all, and build a “Class Leavel Relationship”, and not an “Object Level Relationship”.

Is this possible under Laravel?

Tags:

2

Answers


  1. 0

    Instead of hasMany(), you can create One To Many (Polymorphic) relationship between Post, Page, Image, Video and CustomFieldDefinition.

    More about polymorphic relationships here.

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  2. 0

    There might be a workaround but I’m not pretty sure about it.

    What you could try doing is to define a mutated attribute and set it as the local key of the relationship:

    class Post extends Model
{

   public function getEntityNameAttribute()
   {
       return 'Post';
   }

   public function customFieldDefinitions()
   {
       return $this->hasMany(
           'CustomFieldDefinition',
           'parent_entity_name',
           'entity_name'
      );
   }
}

    You could also go further and define a trait which could be used by all your models which have customFieldDefinitions. It could look like:

    trait HasCustomFieldDefinitionsTrait
{
   public function getEntityNameAttribute()
   {
       return (new ReflectionClass($this))->getShortName();
   }

   public function customFieldDefinitions()
   {
       return $this->hasMany(
           'CustomFieldDefinition',
           'parent_entity_name',
           'entity_name'
      );
   }
}

    Then you can use it wherever needed:

    class Post extends Model
{ 
    use HasCustomFieldDefinitionsTrait;
}

class Video extends Model
{ 
    use HasCustomFieldDefinitionsTrait;
}

class Page extends Model
{ 
    use HasCustomFieldDefinitionsTrait;
}

class Image extends Model
{ 
    use HasCustomFieldDefinitionsTrait;
}
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