The difference between `morphToMany` and `morphedByMany` in Laravel polymorphic many-to-many relationships lies primarily in their roles in the relationship and how the database structure supports them.
Database Structure in Polymorphic Many-to-Many
Polymorphic many-to-many relationships involve three main tables:
- Two model tables (e.g., `posts` and `tags`)
- One intermediate pivot table (e.g., `taggables`)
The pivot table contains at least three columns:
- `tag_id` (the ID of the related model, e.g., tag)
- `taggable_id` (the ID of the model that is related to the tag, e.g., post or video)
- `taggable_type` (the class name or type of the related model, e.g., `App\Models\Post` or `App\Models\Video`)
This structure allows a single pivot table to relate multiple different models to a common model (tags in this case) without needing separate pivot tables for each model combination[5][9].
Role of `morphToMany`
- Used on the model that "owns" or "has" the polymorphic relationship.
- Defines the relationship from the perspective of the model that is related to many other models.
- For example, in a `Post` model, the `tags()` method uses `morphToMany` to get all tags associated with that post.
- This method specifies the related model and the "morph name" (e.g., `'taggable'`), which corresponds to the pivot table columns (`taggable_id` and `taggable_type`).
- It queries the pivot table filtering by the current model's ID and type to find related models[5][9].
Role of `morphedByMany`
- Used on the model that is the target of the polymorphic relationship.
- Defines the inverse side of the polymorphic many-to-many relationship.
- For example, in the `Tag` model, methods like `posts()` or `videos()` use `morphedByMany` to get all posts or videos associated with that tag.
- It specifies the related model class and the same morph name used in `morphToMany`.
- This method queries the pivot table filtering by the related model's type and ID to find all models of that type associated with the current model (tag)[5][9].
Summary of Differences in Database Terms
- `morphToMany` is called on the model that is related to many others, and it uses the pivot table columns `taggable_id` and `taggable_type` to filter records where the `taggable_type` matches the current model's class.
- `morphedByMany` is called on the model that is being related to (the inverse), and it uses the pivot table to find all models of a specific type that relate back to the current model.
Both methods use the same pivot table but differ in the direction of the relationship they represent. The pivot table remains the same, with columns for the related model's ID and type, allowing multiple model types to be linked polymorphically through a single table.
In essence, `morphToMany` defines the relationship from the "parent" or "owning" model side, while `morphedByMany` defines the inverse relationship from the "related" model side, both relying on the same polymorphic pivot table structure[5][9][1].
Citations:
[1] https://laracasts.com/discuss/channels/laravel/difference-between-standard-polymorphic-many-to-many-polymorphic
[2] https://www.sitepoint.com/eloquents-polymorphic-relationships-explained/
[3] https://laraveldaily.com/post/laravel-polymorphic-many-to-many-get-all-related-records
[4] https://laracasts.com/discuss/channels/eloquent/polymorphic-many-to-many-relation-to-multiple-models
[5] https://laravel.com/docs/11.x/eloquent-relationships
[6] https://docs.octobercms.com/3.x/extend/database/relations.html
[7] https://simple-code.agency/blog/development/simplifying-many-to-many-relationships-with-laravel-polymorphic-relations
[8] https://stackoverflow.com/questions/68073778/laravel-polymorphic-many-to-many-relationship-pivot-table-with-relationship-to-a
[9] https://blog.logrocket.com/polymorphic-relationships-laravel/