Polymorphic relationships in Laravel - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a polymorphic relationship in Laravel?

A polymorphic relationship allows a model to belong to more than one other model on a single association. For example, a Comment model can belong to both a Post and a Video model using the same relationship.

intermediate

How do you define a polymorphic one-to-many relationship in Laravel?

Use the morphMany method on the parent model and morphTo on the child model. For example, a Post model has many comments with comments() using morphMany, and Comment uses commentable() with morphTo.

beginner

What database columns are required for polymorphic relationships?

You need two columns on the related table: <code>{relation}_id</code> and <code>{relation}_type</code>. For example, in comments table, <code>commentable_id</code> stores the ID and <code>commentable_type</code> stores the model class name like 'App\\Models\\Post'.

advanced

Can polymorphic relationships be used with many-to-many relationships in Laravel?

Yes, Laravel supports polymorphic many-to-many relationships using morphToMany and morphedByMany methods. This allows a model to belong to multiple models on a many-to-many basis with a single pivot table.

intermediate

Why use polymorphic relationships instead of multiple foreign keys?

Polymorphic relationships simplify the database design by using one set of columns to relate to multiple models. This avoids adding many nullable foreign keys and makes the code cleaner and easier to maintain.

Which two columns are essential for a polymorphic relationship in Laravel?

A model_id and model_type

B foreign_id and foreign_type

C relation_id and relation_type

D id and type

The columns must be named {relation}_id and {relation}_type, for example commentable_id and commentable_type.

Which method defines the inverse side of a polymorphic one-to-many relationship in Laravel?

A belongsTo

B morphMany

C hasMany

D morphTo

morphTo is used on the child model to define the inverse polymorphic relationship.

What does the morphMany method do in Laravel?

A Defines a polymorphic many-to-many relationship

B Defines a polymorphic one-to-many relationship

C Defines a standard one-to-many relationship

D Defines a belongsTo relationship

morphMany defines a polymorphic one-to-many relationship from the parent model.

Which Laravel method is used for polymorphic many-to-many relationships?

A morphToMany

B morphTo

C morphMany

D belongsToMany

morphToMany is used to define polymorphic many-to-many relationships.

Why might you choose polymorphic relationships in your Laravel app?

A To avoid multiple nullable foreign keys and simplify code

B To increase database size

C To make queries slower

D To avoid using Eloquent models

Polymorphic relationships reduce complexity by using one relation for multiple models, avoiding many nullable foreign keys.

Explain how to set up a polymorphic one-to-many relationship in Laravel with an example.

Think about how comments can belong to posts or videos using the same table.

Describe the benefits of using polymorphic relationships over multiple foreign keys in Laravel.

Consider how many models can share the same related data type.

Practice

1. What is the main purpose of polymorphic relationships in Laravel?

easy

A. To allow a model to belong to more than one other model on a single association

B. To create many-to-many relationships between two models

C. To enforce strict foreign key constraints in the database

D. To automatically generate database migrations

Solution

1. Step 1: Understand polymorphic relationships

   Polymorphic relationships allow a model to belong to multiple other models using a single association.

2. Step 2: Compare with other relationship types

   Unlike many-to-many or one-to-many, polymorphic lets one model relate to different models without separate foreign keys.

3. Final Answer:

   To allow a model to belong to more than one other model on a single association -> Option A

4. Quick Check:

   Polymorphic relationships = single association to multiple models [OK]

Hint: Polymorphic = one model relates to many different models [OK]

Common Mistakes:

• Confusing polymorphic with many-to-many relationships
• Thinking it automatically creates migrations
• Assuming it enforces database constraints

2. Which method should you use in the related model to define a polymorphic relationship?

easy

A. morphTo()

B. hasMany()

C. belongsToMany()

D. morphMany()

Solution

1. Step 1: Identify the related model method

   The related model uses morphTo() to define the polymorphic inverse relationship.

2. Step 2: Differentiate from owning model methods

   Owning models use morphMany(), but the related model uses morphTo().

3. Final Answer:

   morphTo() -> Option A

4. Quick Check:

   Related model uses morphTo() [OK]

Hint: Related model always uses morphTo() for polymorphic [OK]

Common Mistakes:

• Using morphMany() in the related model
• Confusing belongsToMany() with polymorphic
• Using hasMany() instead of morphTo()

3. Given the following code, what will $comment->commentable->name output?

class Comment extends Model {
  public function commentable() {
    return $this->morphTo();
  }
}

$comment = Comment::find(1);

Assuming the comment belongs to a Post with name = 'Laravel Tips'.

medium

A. Error: Undefined property 'name'

B. 'Laravel Tips'

C. null

D. 'Comment'

Solution

1. Step 1: Understand morphTo() behavior

   The commentable() method returns the related model instance, here a Post.

2. Step 2: Access the related model's property

   Accessing name on the Post model returns 'Laravel Tips'.

3. Final Answer:

   'Laravel Tips' -> Option B

4. Quick Check:

   commentable->name = 'Laravel Tips' [OK]

Hint: morphTo() returns related model instance [OK]

Common Mistakes:

• Expecting null if not eager loaded
• Confusing property with method call
• Assuming error without checking model relation

4. What is wrong with this polymorphic relationship definition?

class Image extends Model {
  public function imageable() {
    return $this->morphMany();
  }
}

medium

A. morphMany() requires parameters but none are given

B. No relationship method is needed in Image model

C. The method name should be morphable()

D. The method should be morphTo(), not morphMany()

Solution

1. Step 1: Identify the model role

   Image is the related model, so it should use morphTo() for polymorphic inverse.

2. Step 2: Check method used

   morphMany() is for owning models, not related models.

3. Final Answer:

   The method should be morphTo(), not morphMany() -> Option D

4. Quick Check:

   Related model uses morphTo() [OK]

Hint: Related model must use morphTo(), not morphMany() [OK]

Common Mistakes:

• Using morphMany() without parameters
• Wrong method name for polymorphic inverse
• Thinking no method is needed

5. You want to create a polymorphic relationship where both Post and Video models can have many Comment models. Which of the following is the correct way to define the relationship in the Post model?

hard

A. public function comments() { return $this->belongsToMany(Comment::class); }

B. public function comments() { return $this->hasMany(Comment::class); }

C. public function comments() { return $this->morphMany(Comment::class, 'commentable'); }

D. public function comments() { return $this->morphTo(Comment::class, 'commentable'); }

Solution

1. Step 1: Identify owning model relationship

   Post owns many comments via polymorphic relation, so use morphMany().

2. Step 2: Use correct parameters

   morphMany() requires the related model class and the polymorphic name 'commentable'.

3. Final Answer:

   public function comments() { return $this->morphMany(Comment::class, 'commentable'); } -> Option C

4. Quick Check:

   Owning model uses morphMany() with polymorphic name [OK]

Hint: Owning model uses morphMany() with polymorphic name [OK]

Common Mistakes:

• Using hasMany() instead of morphMany()
• Using morphTo() in owning model
• Using belongsToMany() for polymorphic