I know this kind of question was answered many times and there are solutions to it, however, none of them worked for me. I tried #JsonIgnore, #JsonIgnoreProperties #JsonManagedReference/#JsonBackedReference, yet still the debugger shows that user has reference to authority, which has reference to user, which has reference to authority, which has reference to user ... Most importantly it doesn't throw any exceptions. However, I still wonder why does this happen, why it doesn't throw exceptions, and does it affect productivity
My entities are simple: there is a User
#Entity
#Table(name = "users_tb")
#NoArgsConstructor
#Getter
#Setter
public class User {
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
private Long id;
private String username;
private String password;
#OneToMany(mappedBy = "user", fetch = FetchType.LAZY)
private List<Authority> authorities;
}
and Authority
#Entity
#Table(name = "authorities_tb")
#NoArgsConstructor
#Getter
#Setter
public class Authority {
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
private Long id;
private String name;
#ManyToOne(fetch = FetchType.LAZY)
#JoinColumn(name = "user_id")
private User user;
}
the code to retrieve users using JpaRepository<T, V>
#Override
public UserDetails loadUserByUsername(String username) throws UsernameNotFoundException {
var user = userRepository.findUserByUsername(username).orElseThrow(
() -> new UsernameNotFoundException(ERR_USERNAME_NOT_FOUND));
return new CustomUserDetails(user);
}
The debugger output state before return from loadUserByUsername:
user = {User#10781}
> id = {Long#10784}
> username = "John"
> password = "$2a$10$xn3LI/AjqicFYZFruSwve.681477XaVNaUQbr1gioaWPn4t1KsnmG"
> authorities = {PersistentBag#10788} size = 2
> 0 = {Authority#10818}
> id = {Long#10784}
> name = "READ"
> user = {User#10784}
> id = {User#10784}
> username = "John"
> password = "$2a$10$xn3LI/AjqicFYZFruSwve.681477XaVNaUQbr1gioaWPn4t1KsnmG"
> authorities = {PersistentBag#10788} size = 2
> 0 = {Authority#10818}
...
Circular dependencies aren't a problem in themselves with JPA.
There are two potential problems with them:
From a software design perspective circular dependencies create a cluster of classes that you can't easily break up.
You can easily get rid of them in your case by making the relationship a unidirectional one and replace the other direction by a query, if you really have to.
Is it worth it in your case?
It depends how closely your two entities are really related.
I'd try to avoid bidirectional relationships, because it is easy to make mistakes, like not keeping both sides of the relationship in sync.
But in most cases I wouldn't sweat it.
Most software as way more serious design issues.
The other problem occurs when something tries to navigate this loop until its end, which obviously doesn't work. The typical scenarios are:
rendering it into JSON (or XML). This is what #JsonIgnore & Co takes care of by not including properties in the JSON.
equals, hashCode, toString are often implemented to call the respective methods of all referenced objects.
Just as the JSON rendering this will lead to stack overflows.
So make sure to break the cycle in these methods as well.
JPA itself doesn't have a problem with cycles because it will look up entities in the first level cache.
Assuming you load an Authority and everything is eagerly loaded, JPA will put it in the first level cache, before checking the referenced user id. If it is present in the cache it will use that instance.
If not it will load it from the database, put it in the cache and then check for the authorities ids in the cache. It will use the ones found and load the rest.
For those it will again check the user id, but those are the user we just loaded, so it is certainly in the cache.
Therefore JPA is done and won't get lost in a cycle.
It will just skip the annotated
Try not to use the Lombok annotation #Getter and #Setter. Then generate manually getters and setters and use #JsonIgnore on the class member field and the getter, and #JsonProperty on the setter.
#JsonIgnore
private List<Authority> authorities;
#JsonIgnore
// Getter for authorities
#JsonProperty
// Setter for authorities
You can simply annotate the duplicated field with #ToString.Exclude
In you case:
#Data // this includes getter/setter and toString
#Entity
#Table(name = "users_tb")
#NoArgsConstructor
public class User {
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
private Long id;
private String username;
private String password;
#ToString.Exclude
#OneToMany(mappedBy = "user", fetch = FetchType.LAZY)
private List<Authority> authorities;
}
#Data
#Entity
#Table(name = "authorities_tb")
#NoArgsConstructor
public class Authority {
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
private Long id;
private String name;
#ToString.Exclude
#ManyToOne(fetch = FetchType.LAZY)
#JoinColumn(name = "user_id")
private User user;
}
More info: Lombok #Data and #ToString.Exclude
Related
NOTE : Different concepts are not included in order to focus on the problem. It is normally incorrect to use Entity in API requests. In this example, Entities were used in the API architecture to focus only on the problem.
I was making some examples with JPA.
I had to use #JsonIgnore when I was establishing a relationship. When I didn't use JsonIgnore, it went into an infinite loop and gave a serialization error. Then I solved my problem by adding #JsonIgnore annotation to the relevant field.
However, for example, when I want to bring all the users using branch number 1 and branch number 1, I cannot return the list because it marks it with #JsonIgnore. Can I filter #JsonIgnore markup according to rest requests?
If a POST request comes, #JsonIgnore should work, but if a GET request comes, #JsonIgnore should be inactive.
#Entity
#Getter
#Setter
public class Account {
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
private Integer id;
private String name;
private double balance;
#ManyToOne
#JoinColumn(name = "branchCode")
private Branch branch;
}
#Entity
#Getter
#Setter
public class Branch {
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
private Long id;
private String name;
private String address;
#Column(unique = true)
private Integer branchCode;
#OneToMany(mappedBy = "branch")
#JsonIgnore
private List<Account> accounts;
}
Add brach ( POST METHOD )
Get Account ( POST METHOD )
Get Account info ( GET METHOD )
Get Branch ( GET METHOD )
It is possible to add and remove annotations at runtime. Check out this article on the subject. The idea here is that you would set the annotation during a POST call, and remove the annotation during a GET call.
Whether or not this will work with Jackson, or your use case, I do not know, but your question related specifically to "use the #JsonIgnore object conditionally". Whether this approach works or not is something you can determine through experimentation, and hopefully report back with your results.
I have a entity user with self dependency. When i Map this entity to DTO I have the problem of circular dependency. .
User.class:
public class User {
#Id
#GeneratedValue
private Long id;
#NotNull
#Column(name = "first_name")
private String firstName;
#NotNull
#Column(name = "last_name")
private String lastName;
#JsonBackReference
#ManyToMany(
private List<User> friedns_of = new ArrayList<>();
#ManyToMany(cascade = CascadeType.ALL,
mappedBy = "followers")
private List<User> friends = new ArrayList<>();
UserMapper method in UserMapper:
public static UserResponse toUser(User user) {
UserResponse userResponse = new UserResponse();
userResponse.setId(user.getId());
userResponse.setFollowers(user.getFollowers().stream().map(UserMapper::toUser).toList());
userResponse.setFollowing(user.getFollowing().stream().map(UserMapper::toUser).toList());
return userResponse;
}
When i run the method toUser() I get stackOverFlowError exception caused by the infinite circular dependency. Any advise how to solve this?
One way to resolve this is to model the 'follows' relationship as a separate entity:
#Table(name="user_followers")
public class Follows {
#Id
#GeneratedValue
private Long id;
#NotNull
#Column(name = "follower_Id")
private User follower;
#NotNull
#Column(name = "user_id")
private User user;
}
Then you could give your user two one-to-many lists of these entities:
public class User {
#Id
#GeneratedValue
private Long id;
#OneToMany(mappedBy = "user_id")
private List<Follows> followers;
#OneToMany(mappedBy = "follower_Id")
private List<Follows> following;
}
EDIT: instead of the id field in Follows you could use the user_id and follower_id as a composite primary key using #Embeddable. Omitted here for brevity. See here for more details: https://www.baeldung.com/jpa-many-to-many
Since you already have a DTO of UserResponse, you are on the right path towards a correct solution. My suggestion would be to avoid #ManyToMany on an entity level, and manage followers on a service level.
This means you will have to split relation ManyToMany join column into a separate entity, such as UserFollowsEntity with fields userId and followsUserId. Then remove followers and following lists from your User entity entirely.
Now when creating UserResponse in a service, you will have to
Select the actual user from repository – userRepository.findById(userId)
Select followers – userFollowsRepository.findByFollowsUserId(userId)
Select following – userFollowsRepository.findByUserId(userId)
It is a good practice to try and avoid bidirectional in entities relationships entirely if possible.
EDIT: This will give you two lists: followers and following. You will probably want to know their user names, so what you can do is to merge followers and following lists into one, then extract all user ids from that list. Then query user repository with a list of those IDs, and just attach the required user information to your response model.
Yes it does sound like a bit more work compared to the seeming simplicity of utilizing JPA annotations, but this is the best way to avoid circular dependency as well as decouple the Follower functionality from your user entity.
This question already has answers here:
Problem with LazyInitializationException
(2 answers)
Closed 4 months ago.
I have 3 tables in the DB and 3 JPA entities respectively in Java application.
#Data
#Entity
public class Fraud {
#Id
#Column(name = "id")
private Integer id;
#Column(name = "fraud_type")
private String fraudType;
#Column(name = "fraud_value")
private String fraudValue;
#OneToMany(mappedBy = "fraud", fetch = FetchType.EAGER)
private List<FraudActionEntity> fraudActions;
}
#Data
#Entity
public class FraudActionEntity {
#Id
#Column(name = "id")
private Integer id;
#ManyToOne
#JoinColumn(name = "fraud_id")
private Fraud fraud;
#ManyToOne
#JoinColumn(name = "action_id")
private Action action;
#Column(name = "enabled")
private Boolean enabled;
}
#Data
#Entity
public class Action {
#Id
#Column(name = "id")
private Integer id;
#Column(name = "attribute_key")
private String attributeKey;
#Column(name = "attribute_value")
private String attributeValue;
}
#Repository
public interface FraudRepository extends JpaRepository<Fraud, Integer> {
public Fraud findByFraudTypeAndFraudValue(String fraudType, String fraudValue);
}
My use case
On a certain type of fraud, I want to traverse all the actions that triggers from that type of fraud and act on them.
Access code
Fraud fraud = fraudRepository.findByFraudTypeAndFraudValue("Type", "Value");
log.info(fraud.getFraudActions().get(0).getAction());
When I above code runs, everything works OK. I get the fraud and fraudActions associations as well, without getting any error.
I was under the impression that as both entities Fraud and FraudActionEntity are fetching each other eagerly, so it should give some error like cyclic fetch/infinite fetch loop, but it didn't!
Why did it work? And when exactly will give it error like cyclic fetch error OR infinite fetch loop error? And if it does give a cyclic fetch error, can we fix it using lazy fetch at #ManyToOne side as given below:
#ManyToOne(fetch = FetchType.LAZY)
#JoinColumn(name = "fraud_id")
private Fraud fraud;
Update: A simple and very effective work-around towards the LazyInitializationException is to annotate your method with #Transactional annotation. This will create and maintain the transaction while the method is being executed, thereby allowing your code to make the necessary calls to the DB's lazy init objects. Learn more about it here.
The return type of your JPA repository method should be a List of the Entity object, since the result could be more than one row (that is probably why you are getting the null of the fraud variable).
Regarding the Fetch strategy, you could use Eager on that particular association or maybe other strategies. One possible solution would be to make a second query in case you need the lazy-loaded FraudAction list of objects.
Also, as a side-note avoid using lombok data annotation, and always make sure that you have a NoArgsConstructor in your Entity/DTO classes (in your case #Data adds that by accident since it includes #RequiredArgsConstructor and you do not have any final variables.
I have a user entity with an assistant column.
Every user has an assistant but there are circles as well.
For example : User A's assistant is User B and User B's assistant is
user A.
If I use #ManyToOne and #OneToMany annotations, then, there is an infinite recursion when converting objects to JSON, even #JsonManagedReference and
#JsonBackReference didn't help.
BaseEntity:
#MappedSuperclass
#Data
public class BaseEntity {
#Id
#GeneratedValue(strategy = GenerationType.SEQUENCE)
private long id;
#Version
private int version;
}
User:
#Entity
#AllArgsConstructor
#NoArgsConstructor
#Data
#EqualsAndHashCode(callSuper = true)
#Table(name = "Users")
public class User extends BaseEntity {
#Column
private String username;
#Column
private String name;
#JsonManagedReference
#ManyToOne
#JoinColumn(name = "assistant_id")
private User assistant;
#JsonBackReference
#OneToMany(mappedBy = "assistant")
private Set<User> assistants;
}
Are there any opportunity in Spring to solve this?
#JsonManagedReference/#JsonBackReference won't help, because the 'forward' references can still form a cycle, even when the 'inverse' references are not being serialized.
What you want is probably for the User assigned to the assistant property to be serialized without its own assistant property (so that any cycles break). Essentially, you have the same issue as here, except in your case A and B are the same class.
Apart from the solution described in the question I've linked to, you'll also want to specify which #JsonView to use when serializing the object. See the 'Using JSON Views with Spring' section here.
Could you create Assistant entity based on the same table and join?
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.