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Saving entity with one-to-many relationship

I think I have a bad setup for my hibernate database. I have Citizen entities who have one to many relationships with WeeklyCare entities. Below is the relevant code.
Citizen:
#Entity
#Table(name = "citizens")
public class Citizen {
#Id
#Size(max = 10, min = 10, message = "CPR must be exactly 10 characters")
private String cpr;
#OneToMany()
#JoinColumn(name = "cpr")
private List<WeeklyCare> weeklyCare;
}
WeeklyCare:
#Entity
public class WeeklyCare {
#EmbeddedId
private WeeklyCareIdentifier weeklyCareIdentifier;
}
WeeklyCareIdentifier:
#Embeddable
public class WeeklyCareIdentifier implements Serializable {
#NotNull
#Size(max = 10, min = 10, message = "CPR must tbe exactly 10 characters")
private String cpr;
#NotNull
private Integer week;
#NotNull
private Integer year;
}
I have some problems when I want to save data to the database:
I can't save WeeklyCare first, because it requires a Citizen.
When I send the citizens to my backend, the objects contain a list of WeeklyCare. When I try to save the citizens, it gives me this error: Unable to find Application.Models.WeeklyCare with id Application.Models.WeeklyCareIdentifier#b23ef67b
I can solve the problem by clearing the list of WeeklyCare on the Citizen before saving it, and then saving the list of WeeklyCare after, but that feels like a terrible way to do it.
I guess I want hibernate to ignore the list of WeeklyCare when it saves a Citizen, but acknowledge it when it fetches a Citizen. Is this possible? Or is there an even better way to do it? Thanks.

I can't save WeeklyCare first, because it requires a Citizen.
You have the "cpr" identifier used in two entities:
it's the primary Id for Citizen
it's part of the composite Id for WeeklyCare
You could, theoretically speaking, create a list of WeeklyCare (not with the way it is modeled now though) and later update the associations of each WeeklyCare to Citizen.
When I send the citizens to my backend, the objects contain a list of WeeklyCare. When I try to save the citizens, it gives me this
error: Unable to find Application.Models.WeeklyCare with id
Application.Models.WeeklyCareIdentifier#b23ef67b
The best way to map One-To-Many association is bidirectional. This will also save you from some unnecessary queries Hibernate is generating when using #OneToMany with #JoinColumn only.
1) Remove cpr from WeeklyCareIdentifier class (and probably rename the class).
#Embeddable
public class WeeklyCareIdentifier implements Serializable {
#NotNull
private Integer week;
#NotNull
private Integer year;
//constructors, getters, setters
}
2) Remove the composite #EmbeddedId in favor of Long id field:
#Entity
public class WeeklyCare {
#Id
#GeneratedValue
private Long id;
#Embedded
private WeeklyCareIdentifier weeklyCareIdentifier;
//constructors, getters, setters
}
3) Move to bidirectional mapping:
#Entity
#Table(name = "citizens")
public class Citizen {
#Id
#Size(max = 10, min = 10, message = "CPR must be exactly 10 characters")
private String cpr;
#OneToMany(
mappedBy = "citizen",
cascade = CascadeType.ALL, //cascade all operations to children
orphanRemoval = true //remove orphaned WeeklyCare if they don't have associated Citizen
)
private List<WeeklyCare> weeklyCares = new ArrayList<>(); //init collections to avoid nulls
//constructors, getters, setters
//add utility methods to manipulate the relationship
public void addWeeklyCare(WeeklyCare weeklyCare) {
weeklyCares.add(weeklyCare);
weeklyCare.setCitizen(this);
}
public void removeWeeklyCare(WeeklyCare weeklyCare) {
weeklyCares.remove(weeklyCare);
weeklyCare.setCitizen(null);
}
}
and:
#Entity
public class WeeklyCare {
#Id
#GeneratedValue
private Long id;
//having reference to the citizen entity from WeeklyCare
#ManyToOne(fetch = FetchType.LAZY)
#JoinColumn(name = "citizen_cpr")
private Citizen citizen;
#Embedded
private WeeklyCareIdentifier weeklyCareIdentifier;
//constructors, getters, setters
}
I would also recommend to use Long ids for the entities, even if the cpr is unique and so on. Convert the cpr to a normal column and introduce a DB generated ID column which you use in to join with in your internal domain and treat the cpr as a pure user-facing data column.

Spring data JPA: how to enable cascading delete without a reference to the child in the parent?

Maybe this is an overly simple question, but I am getting an exception when I try to delete a user entity.
The user entity:
#Entity
#Table(name = "users")
public class User
{
#Transient
private static final int SALT_LENGTH = 32;
#Id
#GeneratedValue(strategy = GenerationType.AUTO)
private int id;
#NotNull
private String firstName;
#NotNull
private String lastName;
#Column(unique = true, length = 254)
#NotNull
private String email;
// BCrypt outputs 60 character results.
#Column(length = 60)
private String hashedPassword;
#NotNull
private String salt;
private boolean enabled;
#CreationTimestamp
#Temporal(TemporalType.TIMESTAMP)
#Column(updatable = false)
private Date createdDate;
And I have an entity class which references a user with a foreign key. What I want to happen is that when the user is deleted, any PasswordResetToken objects that reference the user are also deleted. How can I do this?
#Entity
#Table(name = "password_reset_tokens")
public class PasswordResetToken
{
private static final int EXPIRATION_TIME = 1; // In minutes
private static final int RESET_CODE_LENGTH = 10;
#Id
#GeneratedValue(strategy = GenerationType.AUTO)
private int id;
private String token;
#OneToOne(targetEntity = User.class, fetch = FetchType.EAGER)
#JoinColumn(nullable = false, name = "userId")
private User user;
private Date expirationDate;
The exception I am getting boils down to Cannot delete or update a parent row: a foreign key constraint fails (`heroku_bc5bfe73a752182`.`password_reset_tokens`, CONSTRAINT `FKk3ndxg5xp6v7wd4gjyusp15gq` FOREIGN KEY (`user_id`) REFERENCES `users` (`id`))
I'd like to avoid adding a reference to PasswordResetToken in the parent entity, becaue User shouldn't need to know anything about PasswordResetToken.

It is not possible on JPA level without creating a bidirectional relation. You need to specify cascade type in User class. User should be owner of the relation and it should provide the information on how to deal with related PasswordResetToken.
But if you cannot have a bidirectional relation I would recommend you to setup relation directly in schema generation SQL script.
If you create your schema via SQL script and not via JPA autogeneration (I believe all serious projects must follow this pattern) you can add ON DELETE CASCADE constraint there.
It will look somehow like this:
CREATE TABLE password_reset_tokens (
-- columns declaration here
user_id INT(11) NOT NULL,
CONSTRAINT FK_PASSWORD_RESET_TOKEN_USER_ID
FOREIGN KEY (user_id) REFERENCES users (id)
ON DELETE CASCADE
);
Here is the documentation on how to use DB migration tools with spring boot. And here is the information on how to generate schema script from hibernate (that will simplify the process of writing your own script).

Parent Entity:
#OneToOne
#JoinColumn(name = "id")
private PasswordResetToken passwordResetToken;
Child Entity:
#OneToOne(mappedBy = "PasswordResetToken", cascade = CascadeType.ALL, orphanRemoval = true)
private User user;
If you want the Password entity to be hidden from the client, you can write a custom responses and hide it. Or if you want to ignore it by using #JsonIgnore
If you don't want the reference in the Parent Entity (User), then you have to override the default method Delete() and write your logic to find and delete the PasswordResetToken first and then the User.

You can use Entity listener and Callback method #PreRemove to delete an associated 'Token' before the 'User'.
#EntityListeners(UserListener.class)
#Entity
public class User {
private String name;
}
#Component
public class UserListener {
private static TokenRepository tokenRepository;
#Autowired
public void setTokenRepository(TokenRepository tokenRepository) {
PersonListener.tokenRepository = tokenRepository;
}
#PreRemove
void preRemove(User user) {
tokenRepository.deleteByUser(user);
}
}
where deleteByPerson is very simple method of your 'Token' repository:
public interface TokenRepository extends JpaRepository<Token, Long> {
void deleteByUser(User user);
}
Pay attention on static declaration of tokenRepository - without this Spring could not inject TokenRepository because, as I can understand, UserListener is instantiated by Hybernate (see additional info here).
Also as we can read in the manual,
a callback method must not invoke EntityManager or Query methods!
But in my simple test all works OK.
Working example and test.

JPA OneToMany insert not setting the id's correctly

I have two entities, let's say
Person.java:
#Entity
public class Person implements Serializable {
#Id
#GeneratedValue(strategy = AUTO)
private long id;
#OneToMany(mappedBy = "personData", cascade = CascadeType.PERSIST)
private List<SkillsData> skillsData;
// ...
}
SkillsData.java
#Entity
#Table(name = "SkillsData")
public class SkillsData implements Serializable {
#Id
#GeneratedValue(strategy = AUTO)
private long id;
#JoinColumn(name = "PERSONID")
#ManyToOne(cascade = REMOVE)
private Person personData;
// ...
}
When I create a person, add a list of type SkillsData to it's skillsData field and persist it everything works with no exceptions thrown, but when I browse the database directly in the SkillsData table the field PERSONID is not populated and because of that the skills added can't be referenced to the right person.
I'm trying to fix this problem for quite some time and I'll be thankful for any help.

The problem might be in the fact that you're not setting SkillsData.personData before persisting leaving it null.
You must set it cause adding SkillsData to the Person.skillsData list is not enough since you declared this side of relationship as inverse(mappedBy attribute).
Therefore it is the SkillsData.personData non-inverse side who is responsible for establishing this relationship.

JPA - OneToMany relationship not loading children

I am trying to configure this #OneToMany and #ManyToOne relationship but it's simply not working, not sure why. I have done this before on other projects but somehow it's not working with my current configuration, here's the code:
public class Parent {
#OneToMany(mappedBy = "ex", fetch= FetchType.LAZY, cascade=CascadeType.ALL)
private List<Child> myChilds;
public List<Child> getMyChilds() {
return myChilds;
}
}
public class Child {
#Id
#ManyToOne(fetch=FetchType.LAZY)
private Parent ex;
#Id
private String a;
#Id
private String b;
public Parent getParent(){
return ex;
}
}
At first, I thought it could be the triple #Id annotation that was causing the malfunction, but after removing the annotations it still doesn't work. So, if anyone have any idea, I am using EclipseLink 2.0.
I just try to execute the code with some records and it returns s==0 always:
Parent p = new Parent();
Integer s = p.getMyChilds().size();
Why?

The problem most probably is in your saving because you must not be setting the parent object reference in the child you want to save, and not with your retrieval or entity mappings per se.
That could be confirmed from the database row which must be having null in the foreign key column of your child's table. e.g. to save it properly
Parent p = new Parent();
Child child = new Child();
p.setChild(child);
child.setParent(p);
save(p);
PS. It is good practice to use #JoinColumn(name = "fk_parent_id", nullable = false) with #ManyToOne annotation. This would have stopped the error while setting the value which resulted in their miss while you are trying to retrieve.

All entities need to have an #Id field and a empty constructor.
If you use custom sql scripts for initialize your database you need to add the annotation #JoinColumn on each fields who match a foreign key :
example :
class Parent {
#Id
#GeneratedValue(strategy=GenerationType.IDENTITY)
private int id;
public Parent() {}
/* Getters & Setters */
}
class Child {
#Id
#GeneratedValue(strategy=GenerationType.IDENTITY)
private int id;
/* name="<tablename>_<column>" */
#JoinColumn(name="Parent_id", referencedColumnName="id")
private int foreignParentKey;
public Child () {}
}

fetch= FetchType.LAZY
Your collection is not loaded and the transaction has ended.

Using JPA mapped by not primary key field?

I am having troubles getting this working and I wonder if what I am doing simply does not make sense?
public class Application {
#Id
#GeneratedValue(strategy = GenerationType.AUTO)
#Column(name="id")
private long id;
....
}
#MappedSuperclass
public abstract class Sample {
#Id #GeneratedValue(strategy = GenerationType.AUTO)
private long id;
#OneToOne (cascade=CascadeType.ALL)
protected Application application;
....
}
// TestSample contains a list that is mapped not by the primary key of the Sample
public class TestSample extends Sample {
#OneToMany(mappedBy="application", cascade=CascadeType.ALL, fetch=FetchType.LAZY)
private List<Part> parts = new ArrayList<Part>();
....
}
public class Part {
#Id #GeneratedValue(strategy = GenerationType.AUTO)
private long id = 0;
#ManyToOne (cascade=CascadeType.ALL, fetch=FetchType.LAZY)
Application application;
}
The problem I am having is that I am able to add parts, the database looks correct, then when I attempt to fetch the the parts list I get an empty list.
I can get it to work if I compromise on the database structure by changing these classes:
// TestSample contains a list that is mapped not by the primary key of the Sample
public class TestSample extends Sample {
#OneToMany(mappedBy="testSample", cascade=CascadeType.ALL, fetch=FetchType.LAZY)
private List<Part> parts = new ArrayList<Part>();
....
}
public class Part {
#Id #GeneratedValue(strategy = GenerationType.AUTO)
private long id = 0;
#ManyToOne (cascade=CascadeType.ALL, fetch=FetchType.LAZY)
TestSample testSample;
}
The tables are being auto generated by hibernate, so they are coming out like this:
application
id : number
....
test_sample
id : number
application_id : number
...
part
id : number
application_id : number
If I change it to the less desirable way that works, the last table is different:
part
id : number
test_sample_id : number
Because the id's in all cases are being auto generated, there are no shared primary keys. Essentially what I am trying to do is use mappedby where mappedby is referring to a field that is not the primary key of the table/class called "TestSample". This is what I am not sure if makes sense in JPA.

The OneToMany is bi-directional with the "Part" class. I think this is getting very difficult to explain (:
Your one-to-many association between TestSample and Part is not bidirectional, the mappedBy is not correct (the application table is not owning the relation, it is not even aware of test_sample), your mapping doesn't make sense. There is something to change.
I think that you should show what the expected tables are, not the generated one (since the mappings are incoherent, the generated result can't be satisfying). You are talking about compromise so I believe that you have an idea of what the expected result should be. Please show it.