HasMany

Table of contents

1. Overview
2. Defining
   1. Custom local key
3. Using
   1. Constraints
4. Method reference

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Overview

Part of the Relations family: HasOne, HasMany, BelongsTo, BelongsToMany.

HasMany<T> represents a one-to-many relationship where the foreign key lives on the related model. This model is the parent; the related model stores a reference back to it.

users            posts
──────────────   ───────────────────
id  (PK)    ←──  user_id  (FK)
name             title
                 published

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Defining

Override a method in your model and call the protected hasMany() helper:

public class User extends Model {

    private final ModelRepository<Post> postRepo;

    public User(String id) { super(id); }

    /** One-to-many: "user_id" column lives on the Post table. */
    public HasMany<Post> posts() {
        return hasMany(postRepo, "user_id");
    }
}

Custom local key

By default hasMany uses this model’s id as the anchor value. Pass a third argument to use a different attribute:

public HasMany<Post> posts() {
    return hasMany(postRepo, "author_ref", "uuid"); // resolves posts WHERE author_ref = this.uuid
}

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Using

// Load all related posts
List<Post> allPosts = user.posts().get();

// Count without loading models
long count = user.posts().count();

Constraints

WHERE, ORDER BY, and LIMIT can be chained before calling .get() or .count():

List<Post> recent = user.posts()
    .where("published", true)
    .orderBy("created_at", false)
    .limit(5)
    .get();

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Method reference

Method	Return type	Description
where(column, value)	HasMany<T>	Add WHERE column = value constraint
orderBy(column, asc)	HasMany<T>	Sort results
limit(n)	HasMany<T>	Cap the maximum number of results
get()	List<T>	Return all matching related records
count()	long	Number of matching related records