ManyToMany relation: save the transient instance before flushing

Question

While saving data to DB, I'm getting an exception org.hibernate.TransientObjectException : object references an unsaved transient instance - save the transient instance before flushing: com.example.api.entity.Product

I have two entities.

User.java

@Entity
@Table(name = "users", schema = "public")
public class User {

    @Id
    @Column(name = "user_id", updatable = false, nullable = false, unique = true)
    @GeneratedValue(generator = "UUID")
    @GenericGenerator(name = "UUID", strategy = "org.hibernate.id.UUIDGenerator")
    private UUID id;
    @Column(name = "name")
    private String name;

    @Column(name = "product")
    @ElementCollection(targetClass = Product.class)
    @ManyToMany(fetch = FetchType.LAZY, cascade = {CascadeType.PERSIST, CascadeType.MERGE})
    @JoinTable(name = "products_users",
            joinColumns = {@JoinColumn(name = "user_id")},
            inverseJoinColumns = {@JoinColumn(name = "product_id")})
    private Set<Product> products;

    @JsonFormat(shape = JsonFormat.Shape.STRING, pattern="yyyy-MM-dd@HH:mm:ss")
    @Column(name = "created_on")
    @JsonIgnore
    private Date createdOn;
    @JsonFormat(shape = JsonFormat.Shape.STRING, pattern="yyyy-MM-dd@HH:mm:ss")
    @Column(name = "modified_on")
    @JsonIgnore
    private Date modifiedOn;

//getters, setters, contructors
}

Product.java

@Entity
@Table(name = "product", schema = "public")
public class Product {

    @Id
    @Column(name = "product_id", updatable = false, nullable = false, unique = true)
    @GeneratedValue(generator = "UUID")
    @GenericGenerator(name = "UUID", strategy = "org.hibernate.id.UUIDGenerator")
    private UUID id;
    @Column(name = "name")
    private String name;

    @JsonFormat(shape = JsonFormat.Shape.STRING, pattern="yyyy-MM-dd@HH:mm:ss")
    @Column(name = "created_on")
    @JsonIgnore
    private Date createdOn;

    @JsonFormat(shape = JsonFormat.Shape.STRING, pattern="yyyy-MM-dd@HH:mm:ss")
    @Column(name = "modified_on")
    @JsonIgnore
    private Date modifiedOn;

//getters, setters, contructors
}

And I have a JSON with data to add.

{
"name": "Max",
"products": [{
        "name": "product1",
        "createdOn": "2019-07-26T11:13:39",
        "modifiedOn": "2019-07-26T11:13:39"
    }
],
"createdOn": "2019-07-26T11:13:39",
"modifiedOn": "2019-07-26T11:13:39"

}

I read about this exeption and tried to change CascadeType to another, but it doesn't help.

Answer 1

I think you must remove the ElementCollection annotation. The ManyToMany annotation is enough.

You could try to add the relationship on the Product class too