Hibernate 2 primary keys (1 is a foreign key)

Question

My question is about the code below:

Ingredient.java

@Entity
@Table(name = "recipes_ingredients")
public class Ingredient implements Serializable {
 
    @Id
    @Column(name = "ingredient_id")
    private Long id;
 
    @NotEmpty
    private String name;
 
    private Integer quantity;
 
    // Getters and Setters
}

Recipe.java

@Entity
@Table(name = "recipes")
public class Recipe implements Serializable {
 
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name = "recipe_id")
    private Long id;
 
    @NotEmpty
    private String name;
 
    @ManyToOne(fetch = FetchType.LAZY)
    private Client client;
 
    @OneToMany(fetch = FetchType.LAZY, cascade = CascadeType.ALL, orphanRemoval = true)
    @JoinColumn(name = "fk_recipe_id")
    private List<Ingredient> ingredients;
 
    // Getters and Setters
}

What I want to do is that the PK (recipes_ingredients table) is composed of: ingredient_id and recipe_id in some way (using the FK that I already have and making it also PK or just taking that ID in some other way and making it PK with ingredient_id).

The ingredient_id will be numbers that will start at 1 onwards for each recipe, in this way if I have a recipe with recipe_id = 1 and 3 ingredients, my idea is that in the ingredients table it has something like this:

ingredient_id(PK)    name      quantity   recipe_id(PK)
1                    Oil       150        1
2                    Salt      5          1
3                    Flour     500        1

Any idea how I can do this?

Answer 1

    public class IngredientId {

        private Recipe recipe;

        private Long id;

        public IngredientId(Recipe recipe, Long id) {
            this.recipe = recipe;
            this.id = id;
        }

        public IngredientId() {
        }

        //Getters and setters are omitted for brevity

        public Recipe getRecipe() {
            return recipe;
        }

        public void setRecipe(Recipe recipe) {
            this.recipe = recipe;
        }

        public Long getId() {
            return id;
        }

        public void setId(Long id) {
            this.id = id;
        }

        @Override
        public boolean equals(Object o) {
            if ( this == o ) {
                return true;
            }
            if ( o == null || getClass() != o.getClass() ) {
                return false;
            }
            IngredientId ingredientId = (IngredientId) o;
            return Objects.equals( recipe, ingredientId.recipe ) && Objects.equals( id, ingredientId.id );
        }

        @Override
        public int hashCode() {
            return Objects.hash( recipe, id );
        }
    }

    @Entity
    @IdClass( IngredientId.class )
    @Table(name = "recipes_ingredients")
    public class Ingredient {

        @Id
        @ManyToOne(fetch = FetchType.LAZY)
        @JoinColumn(name = "recipe_id")
        private Recipe recipe;

        @Id
        @GeneratedValue
        @Column(name = "ingredient_id")
        private Long id;

        private String name;

        private Integer quantity;

        public IngredientId getId() {
            return new IngredientId( recipe, id );
        }

        public void setId(IngredientId id) {
            this.recipe = id.getRecipe();
            this.id = id.getId();
        }
    }

    @Entity
    @Table(name = "recipes")
    public class Recipe {

        @Id
        @GeneratedValue(strategy = GenerationType.IDENTITY)
        @Column(name = "recipe_id")
        private Long id;

        private String name;

        @OneToMany(fetch = FetchType.LAZY, cascade = CascadeType.ALL, orphanRemoval = true)
        @JoinColumn(name = "recipe_id")
        private List<Ingredient> ingredients = new ArrayList<>();

    }

It's important to notice that a composite key cannot have null values. So this makes sense only if you know that each ingredient is bound to a recipe. See this answer on StackOverflow and this Hibernate Jira

You can have a look at the Hibernate ORM documentation for more details.