How to remove object from list without removing that parent object in many to many relationship?
I have ticketEntity with set of offenceEntity:
public class TicketEntity {
#Id
private String id;
#ManyToMany
#JoinTable(
name = "offences_in_tickets",
joinColumns = #JoinColumn(name = "ticket_id"),
inverseJoinColumns = #JoinColumn(name = "offence_id"))
private Set<OffenceEntity> offences;
}
and OffenceEntity with set of TicketEntity:
public class OffenceEntity {
#Id
#Column(name="id")
private String id;
private String name;
#ManyToMany(mappedBy="offences", cascade = CascadeType.ALL)
private Set<TicketEntity> tickets;
}
Should I change cascade type? Now when I remove one of OffenceEntity from database I am removing TicketEntity too, but I would like to delete only Offence.
I don't know what "parent" or "child" is, or what you mean by "removing from list", as there is no list in your examples. If you want an answer to your questions, please invest more time in writing up a proper question and try to re-read the question with the mindset of someone who doesn't work on this problem. Maybe ask a colleague if the question is immediately understandable before posting this.
Having said that, I can only assume that "parent" refers to TicketEntity and "child" refers to OffenceEntity.
So if you want to remove the many-to-many relationship between two such objects, you simply have to load the TicketEntity and remove the respective OffenceEntity from the offences set e.g. like this:
entityManager.find(TicketEntity.class, ticketId)
.getOffences()
.remove(
entityManager.find(OffenceEntity.class, offenceId)
);
Related
Post entity:
public class Post {
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
#Column(name = "id")
private Long id;
#OneToMany(mappedBy = "post")
private List<PostComment> postComments;
...
}
PostComment entity:
public class PostComment {
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
#Column(name = "id")
private Long id;
#ManyToOne
#JoinColumn(name = "post_id")
private Post post;
#OneToMany(mappedBy = "postComment")
private Set<PostCommentUpvote> postCommentUpvotes;
#OneToMany(mappedBy = "postComment")
private Set<PostCommentDownvote> postCommentDownvotes;
...
}
PostCommentUpvote entity (PostCommentUpvote and PostCommentDownvote have the exact same fields - these entities act like counters)
public class PostCommentUpvote {
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
#Column(name = "id")
private Long id;
#ManyToOne
#JoinColumn(name = "post_comment_id")
private PostComment postComment;
#ManyToOne
#JoinColumn(name = "user_id")
private User user;
...
}
All relations are bi-directional as you can see from the annotations.
The goal: When a user (authenticated) upvotes/downvotes a PostComment I want to do the following:
Check if user already upvoted/downvoted the PostComment.
For this I have Post id (even though this is not needed) and PostComment id and both are indexed.
There are three possible 'states' when User up/downvotes the comment:
User hasn't yet up/downvoted that comment, so it is either new upvote or new downvote
User has already upvoted and if he upvotes again, it will remove the upvote (same with downvote)
User has already upvoted and if he downvotes, upvote is removed and new downvote is added (and vice-versa)
What would be the most optimal way of doing this? Get the PostComment by its id and then loop through the List of PostCommentUpvote/PostCommentDownvote and check the User on every iteration? Or perform a tactical SQL request, which must be faster than looping in Java? If so, what would this SQL query look like? Or any other approach to make this performant. I am open to any suggestion.
Thanks
Assuming you have the post comment id and user id, the following JPA query (or close to it) will return true if the user has upvoted on the post comment and false otherwise:
select case when count(postCommentUpvote) > 0 then 'true' else 'false'
from PostCommentUpvote postCommentUpvote
join postCommentUpvote.postComment postCommnent
where postComment.id = :postCommentId
and user.id = :userId
You would then have to perform the same query using the PostCommentDownVote entity. An alternative would be to remove the up and down vote entities, simply create a PostCommentVote entity which has a boolean attribute that indicates up or down, and helper methods isUpvote() and isDownVote() that would interpret the boolean for you. You could get everything you need with a single query that returns a PostCommentVote if the user has up or down voted and null otherwise.
You did not indicate what you want to do if the user has already commented on the post; ignore the request or update the PostComment. Either way the most optimal way of doing this would be not checking at all. Create a unique index on (user_id, post_comment_id) or drop the the id column and make a composite PK of those columns. Then just insert without checking. Use the On Conflict to either ignore or update the request. You may also want to add an Up/Down vote indicator column.
I have a Parent User Class that has multiple ManyToMany Relationships.
#Table(name = "user")
public class User {
..
#ManyToMany(fetch = FetchType.LAZY, cascade = {CascadeType.MERGE, CascadeType.DETACH})
#JoinTable(
name = "user_address",
joinColumns = { #JoinColumn(name = "user_id")},
inverseJoinColumns = { #JoinColumn(name = "address_id")}
)
#JsonIgnore
private final List<Address> addresses = new ArrayList<Address>();
#ManyToMany(fetch = FetchType.LAZY, cascade = {CascadeType.MERGE, CascadeType.DETACH})
#JoinTable(
name = "reports",
joinColumns = { #JoinColumn(name = "user_id")},
inverseJoinColumns = { #JoinColumn(name = "reports_id")}
)
#JsonIgnore
private final List<Reports> reports = new ArrayList<Reports>();
}
When I access the FIRST ManyToMany property, everything works fine. However, immediately after
accessing the first, when I try to access the SECOND ManyToMany Property I get the "could not initialize proxy - no Session" exception:
#Component
public class Combiner {
public void combineData() {
...
List<Address> addresses = user.getAddress(); // This works
List<Reports> reports = user.getReports(); // Get the error here
..
}
}
The Address and Reports classes have the inverse relationship as many ManyToMany back to the User Entity Above.
public class Address {
#ManyToMany(mappedBy = "addresses", fetch = FetchType.LAZY)
private final List<User> users = new ArrayList<User>();
}
public class Reports {
#ManyToMany(mappedBy = "reports", fetch = FetchType.LAZY)
private final List<User> users = new ArrayList<User>();
}
I tried searching SO for the same error where there are MULTIPLE relationships like mine and the first passes but second fails, but could'nt find a post (or google couldn't understand the search terms, if anyone knows a pre-existing one - please let me know).
Could someone assess what else Im missing?
I've tried these so far to no avail:
Added #Transactional to the parent Service class that calls Combiner above
Made the second failing relationship EAGER. (as i understand it you cant make BOTH EAGER since i get a multiple bags error probably because of Cartesian join)
AM Using SpringBoot (2.2.4) with Hibernate Core {5.4.10.Final}
Approach one:
Make #ManyToMany uni-directional. The exception clearly says it can not initialize the collection of role you have in User class.
As you asked in the comment section Why can't this use case be Bi Directional - You can make this bi-directional as well.
Approach two: make collection of role EAGER or use Hibernate.initialize() to initialize the collection.
Bonus: you can make both collection EAGER by using Set not List.
I need for a project to join 2 SQL tables implemented like this :
I know that I'm not supposed to implement the table IngredientList as an object cause it's only here for SQL structure.
My code goes like this :
#Entity
#Table(name="recipe")
public class Recipe {
#Id
#GeneratedValue(strategy=GenerationType.AUTO)
#Column(name="id_recipe")
private Long id;
#OneToMany
#JoinTable(name="liste_ingredients", joinColumns = #JoinColumn(name = "id_recette",
referencedColumnName = "id_recette"),
inverseJoinColumns = #JoinColumn(name = "id_ingredient",
referencedColumnName = "id_ingredient"))
List<Ingredient> ingredients;
/* Getter/Setter/Constructor */
}
Which is the classic way but with that I lose the Quantity attribute that I want to associate with ingredient. And I don't get how I can work around this without creating an object IngredientList.
Thanks in advance.
Nevermind that I got my answer gonna edit it soon with code, for anyone with the same question.
I'm using #version annotation in spring data so I have a parent entity, and it has list of child entity. when I delete an element from child list the parent version doesn't increase. can anyone clarify for me this #version alternative,
why the versing in this case doesn't increase, is it a good way to manage versioning or should I use trasaction "lock".
in the documentation i read that the version update only on updating a row
in the databse but in my case i put version on parent entity and i want
note: i searched a lot in the internet but i didnt find a clear solution, can any one help me.
I assume you are using Hibernate. Lets say that the "UnderlyingPerTradingAccount" table has a column called "trading_account_id", which is a foreign key to the TradingAccount table. In order to achieve the behavior you described, you need to change the mapping. Can you try this:
public class TradingAccount {
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
private Long id;
#OneToMany(cascade = CascadeType.ALL, orphanRemoval = true)
#JoinColumn(name="trading_account_id", referencedColumnName = "trading_account_id", insertable = false, updatable = false)
private List<UnderlyingPerTradingAccount> underlyingPerTradingAccounts;
#Version
private Long version;
}
and
public class UnderlyingPerTradingAccount {
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
private Long id;
#ManyToOne
#JoinColumn(name="trading_account_id", nullable = false)
private TradingAccount tradingAccount;
private Boolean enableBuy;
private Boolean enableSell;
}
This should mark the parent entity as "dirty" when the child entity is updated and trigger the version increment.
However, I would think of some other method to track "version" changes of the parent entity as this would just cause an additional overhead and update statements to the parent.
I faced the problem when I need to partially udate data in BD.
What I have:
I have three linked entities:
Profile --(1-m)--> Person --(1-1)--> Address
Where Person -> Address is lazy relationship. It was achieved via optional=false option (that allow hibernate to use proxy).
What the problem:
I need to update Profile in such way, that I needn't pull all Addresses that linked with this profile.
When I update Profile (don't work):
profile.setPersons(persons);
session.saveOrUpdate(profile);
throws: org.springframework.dao.DataIntegrityViolationException: not null property references a null or transient value
It happens because Person->Address relationship has optional=false option
I need to do:
//for each person
Address address = requestAddressFromDB();
person.setAddress(address);
persons.add(person)
//and only then
profile.setPersons(persons);
session.saveOrUpdate(profile);
profile.setPerson(person)
But I don't want to pull all address each time I update Profile name.
What is the question:
How can I avoid obligatory Person->(not null)Address constraint to save my profile without pulling all addresses?
ADDITION:
#Entity
public class Person{
#Id
#SequenceGenerator(name = "person_sequence", sequenceName = "sq_person")
#GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "person_sequence")
#Column(name = "id")
private long personID;
#OneToOne(mappedBy="person", cascade=CascadeType.ALL, optional = false, fetch = FetchType.LAZY)
private Address address;
//.. getters, setters
}
#Entity
public class Address {
#Id
#Column(name="id", unique=true, nullable=false)
#GeneratedValue(generator="gen")
#GenericGenerator(name="gen", strategy="foreign", parameters=#Parameter(name="property", value="person"))
private long personID;
#PrimaryKeyJoinColumn
#OneToOne
private FileInfo person;
}
Modify the cascade element on the #OneToOne annotation so that the PERSIST operation is not cascaded. This may require you to manually persist updates to Address in certain areas of your code. If the cascade is not really used however no change is needed.
#OneToOne(mappedBy="person", cascade={CascadeType.MERGE, CascadeType.REMOVE, CascadeType.REFRESH}, optional = false, fetch = FetchType.LAZY)
private Adress address; //Do you know that Address is missing a 'd'?