HasMany

A "one-to-many" relationship is another essential type of database association. Let's illustrate this with an example where we have a User model associated with a Post model. To establish this connection, we define a method called posts within the User model. This posts method invokes the HasMany method and returns its output, representing that a user can have multiple posts in the database. This relationship allows us to easily retrieve all the posts associated with a specific user when needed.

HasMany Class Structure

class HasMany {
    final Type model;
    final String? foreignKey;
    final String? localKey;
    final Function? onQuery;
    final bool? eager;

    const HasMany(this.model,
        {this.foreignKey, this.localKey, this.onQuery, this.eager});
}

User ModelPost Model

@DoxModel()
class User extends UserGenerator {
    @Column()
    String? name;

    @HasMany(Post)
    Post? posts;
}

@DoxModel()
class Post extends PostGenerator {
    @Column()
    String? userId;

    @Column()
    String? title;

    @Column(name: 'desc')
    String? description;

    @Column()
    String? status;
}

Usage

$getRelation

User? user = await User().find(1);
await user?.$getRelation('blogs')

List<Blog> blogs = user?.blogs;

Info

When eager is true the $getRelation do not need to call.

preload

User? user = await User().preload('blogs').find(1);
List<Blog> blogs = user?.blogs;

Info

When eager is true the preload do not need to call.

related

User? user = await User().find(1);
List<Blog> activeBlogs = await user?.related<Blog>('blog')?.where('status', 'active').get();

Options

model

@HasMany(Post)
Post? posts;

foreignKey

@HasMany(Post, foreignKey: 'user_id')
Post? posts;

localKey

@HasMany(Post, foreignKey: 'user_id', localKey: 'id')
Post? posts;

onQuery

@DoxModel()
class User extends UserGenerator {
    @HasMany(Post)
    Post? posts;

    @HasMany(Post, onQuery: activePostQuery)
    Post? activePosts;

    static QueryBuilder<Post> activePostQuery(Post q) {
        return q.where('status', 'active');
    }
}

Info

onQuery method must be a static method inside the model.

eager

@HasMany(Post, eager: true)
Post? posts;