October 31st, 2023

Demystifying the attach() and sync() Methods in Laravel: Streamlining Many-to-Many Relationships

Demystifying the attach() and sync() Methods in Laravel: Streamlining Many-to-Many Relationships

Laravel simplifies database management, particularly when dealing with many-to-many relationships. The framework offers eloquent methods like attach() and sync() that streamline the process of managing relationships between associated entities. In this article, we'll explore the functionalities, differences, and best practices of attach() and sync() methods in the context of many-to-many relationships within Laravel.

Understanding Many-to-Many Relationships in Laravel

Many-to-many relationships occur when multiple records in one database table are related to multiple records in another table through an intermediary table, often referred to as a pivot table. In Laravel, this relationship is established using the belongsToMany() method in the model definitions.

For instance, considering a scenario where we have Students and Courses, a student can enroll in multiple courses, and a course can have multiple students enrolled. Laravel eloquently handles this relationship by providing easy-to-use methods like attach() and sync() for managing the association between these entities.

The attach() Method

The attach() method in Laravel is used to add records to the pivot table that connects related entities in a many-to-many relationship. When you want to associate a new record with an existing entity, the attach() method is utilized.

1$student = Student::find($studentId);

The attach() method requires the ID of the related entity (course in this case) to create a new entry in the pivot table, connecting the student to the course.

Use Cases for attach()

  • Adding new relationships or create relationships between existing entities
  • Handling additional pivot table data such as timestamps or additional attributes

The sync() Method

On the other hand, the sync() method in Laravel is used to synchronize the relationship between entities. It's particularly handy when you need to update the relationships to match a given array of IDs, replacing the existing relationships with the new ones provided.

1$student = Student::find($studentId);
2$student->courses()->sync([$courseId1, $courseId2, $courseId3]);

The sync() method updates the pivot table with the provided IDs, ensuring that the associated courses match the provided array. It attaches new IDs, detaches missing ones, and retains existing ones as per the provided array.

Use Cases for sync():

  • Updating relationship between entities based on a provided array of IDs
  • Replacing existing relationships with the new set of records

Best Practices and Considerations

Both methods can handle additional data in the pivot table, which can be passed as an associative array. When using sync(), be cautious as it overwrites the existing relationships. It removes records not present in the provided array.


Understanding the attach() and sync() methods in Laravel is crucial for managing many-to-many relationships effectively. These eloquent methods provide developers with the flexibility to add, update, and maintain relationships between entities, simplifying complex database interactions.

The choice between attach() and sync() depends on whether you want to add new relationships or update existing ones, offering a level of control and precision when dealing with complex relationships.

Statamic Ninja


Marian Pop

PHP / Laravel Developer. Writing and maintaining @LaravelMagazine. Host of "The Laravel Magazine Podcast". Pronouns: vi/vim.

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