hasMany

hasMany is a data relationship used in object-relational mapping and data modeling to express a one-to-many association. In a hasMany relationship, a single instance of a parent model is related to multiple instances of a child model. The foreign key linking the two is typically stored on the child table, pointing to the parent, which means the parent owns a collection of children.

The exact syntax varies by framework, but the concept is the same: the parent exposes a collection of its children. Examples include Laravel Eloquent: public function posts() { return $this->hasMany(Post::class); }. Rails: has_many :posts. Sequelize: Parent.hasMany(Child, { foreignKey: 'parentId' }). In each case, the child table holds the foreign key.

Accessing and manipulating related records is usually straightforward: you can read the collection (e.g., user.posts) and add new children through the parent (e.g., user.posts.create({...}) or by setting the foreign key on a new child). Deletion rules and constraints are commonly configurable, such as cascade delete when the parent is removed.

Performance considerations include the potential for the N+1 query problem if related data is loaded separately. Eager loading can mitigate this by fetching parents and their children in as few queries as possible. hasMany is often paired with the belongsTo relation on the child side, and it contrasts with many-to-many relationships that require a join table.