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JPA one-to-one mapping creates an extra column. How to remove it?

I have one-to-one mapping JPA table in my springboot application which works fine.
The Users is the parent table and in the account_no column, it stores the foreign key. Which is, child's primary key. The child is Account table.
However, when the application is started, I can see that there is one additional column (user_id) that has been created in H2 DB. I think it is something wrong with my JPA mapping. Pls help to figure it out. Below are the two classes.
#Entity
public class User extends AbstractEntity {
// Other fields related to user entity go here ..
#OneToOne(cascade = CascadeType.ALL, fetch = FetchType.LAZY, optional = false)
#JoinColumn(name = "account_no", referencedColumnName = "account_num")
private Account account;
}
#Entity
public class Account extends AbstractEntity{
// fields like account#, balance etc goes here..
#Column(name="account_num", unique = true)
#NotNull
private long accountNo;
#OneToOne (fetch = FetchType.LAZY)
private User user;
}
Startup log.
create table account (id bigint not null, account_num bigint not null, bal float not null, user_id bigint, primary key (id))
2021-12-22 00:09:28.765 DEBUG 25380 --- [ main] org.hibernate.SQL :

Decide which side should contain the extra column and use the mappedBy attribute. Then JPA will do what's needed
#OneToOne(cascade = CascadeType.ALL, fetch = FetchType.LAZY, optional = false, mappedBy = "user")
private Account account;
Considering that you have bidirectional mapping you don't need the #JoinColumn that you have used.
Just both #OneToOne annotations and the decision which would be owner entity of the relation by using the mappedBy attribute on one of those annotations.

It depends on you in which side you store the extra column which was a
foreign key.Because When You started to established oneToOne
relationship between two table it is mandatory to store user's
primary key in account table as a foreign key, or account table
primary key in user table as foreign key.You should be need to declare
mappedBy and your tables reference name.for example if you declare
mappedBy="user" in account table it create an extra account_id column
in user table as a foreign key, Same as for account
#OneToOne(optional = false, mappedBy = "user")
private Account account;
Don't need to declare these things in side OneToOne annotation cascade
= CascadeType.ALL, fetch = FetchType.LAZY, By default it always support lazy fetch
.

JPA ManyToOne Cascade On UPDATE with JPQL

I have this Parent class
#Entity
#Table(name = "category")
#NamedQuery(name = "category.findAll", query = "SELECT c FROM Category c")
public class Category implements Serializable {
public Category(){}
#Column(name = "name", nullable = false)
#Id
private String name;
#Column(name = "col2")
private Boolean col2;
}
And i have referenced the parent table in child table as follows:
#ManyToOne(cascade = {CascadeType.ALL})
#JoinColumn(name = "cat_name")
private Category category
when i run this JPQL query
update Category c SET c.name=:newName ,c.termsCanHaveChildren=:canHaveChdrn where c.name=:oldName
it's return with foreign key constraint error while i have put Cascade All in child field
Cannot delete or update a parent row: a foreign key constraint fails (`terms`.`term`, CONSTRAINT `FKaykenypxci167nqioh4xx9p3a` FOREIGN KEY (`cat_name`) REFERENCES `category` (`name`))

The problem lays at the constraint being generated by your persistence provider (hibernate), for the #JoinColumn(name = "cat_name") at the child table (and not with the CascadeType that you're defining)...
The generated constraint should indicated that when the PK of Category is Updated, any reference to such column should be updated also...
I believe this configuration should work (but you need to test it first, because I always generated my database model using scripts and not using hibernate features):
#ManyToOne
#JoinColumn(
name = "cat_name",
foreignKey = #ForeingKey(
name = "fk_child_category",
foreignKeyDefinition = "FOREIGN KEY (cat_name) REFERENCES category ON UPDATE CASCADE"
)
)
private Category category;
Also you need to check if your database supports "ON UPDATE CASCADE"... According to this link, oracle does not... (What database are you using?)
If this does not work, try the suggestion of Michelle...

That's expected: you are changing the Primary Key (#Id), that's used in a Foreign Key (#JoinColumn).
Use a surrogated immutable primary key.

Hibernate - How to use a generator to create a primary key for a reference table?

I'am struggling to get Hibernate (with MySQL) to generate the primary key for a reference table from a "main table". My problem is that I got a big table with 25 mil rows and now I need to add multiple additional columns and because in the future where will be even more columns to add I choose the way to work with reference tables instead of adding the columns to the main table (the rebuild takes hours... :)
So there is a main table and a reference table. In my conception the primary key of the reference table should be generated from the primary key of the main table. I could first insert an entry into the main table, then select it and use its primary key for the insert into the reference table, but this seems not to be the best way to me. So I would like to use Hiibernate's generators, but I can't figure out how.
Here's the main table:
#Entity
#Table
public class Task {
#Id
#GeneratedValue
#Column()
private Integer id;
// ...
#OneToOne(mappedBy = "task_ref", orphanRemoval=true, fetch = FetchType.LAZY, cascade = CascadeType.ALL)
private Stuff stuff;
// ...
}
And the reference table:
#Entity
#Table
public class Stuff {
#Id
#Column(name = "stuff_id")
#GeneratedValue()
private Integer stuff_id;
// ...
#OneToOne(orphanRemoval=true, fetch = FetchType.LAZY, cascade = CascadeType.ALL)
#PrimaryKeyJoinColumn
private Task task_ref;
// ...
}
So.. how can I use a generator to create the primary key for the table Stuff from the primary key of the table Task ?
Any suggestions or other solutions are highly welcome!
Thanks!

This is how you should map your bidirectional OneToOne association with a shared primary key:
#Entity
#Table
public class Task {
#Id
#GeneratedValue
private Integer id;
// ...
#OneToOne(mappedBy = "task_ref", orphanRemoval=true, fetch = FetchType.LAZY, cascade = CascadeType.ALL)
private Stuff stuff;
// ...
}
#Entity
#Table
public class Stuff {
#Id
#Column(name = "stuff_id")
private Integer stuff_id;
// ...
#OneToOne(fetch = FetchType.LAZY)
#MapsId
#JoinColumn(name = "stuff_id")
private Task task_ref;
// ...
}
Only the parent needs to cascade to the Child entity, not the other way around.
The Parent only has an "inverse" side of the association.
The shared primary key is both a primary key and a foreign key in the Child entity
The MapsId annotation allows you to share the primary key for both the #Id and the OneToOne association

You could use the Task object as your id, see EmbeddedId or IdClass for an example. In case Stuff represents a subclass of the Task entity in your domain model, you should model this entity as such, in which you will have to represent the Stuff entity as a Joined Subclass of the Task entity. In both cases the extra Id in the Stuff entity is not needed anymore.

JPA #JoinTable - Three ID Columns

I have a situation that is quite similar to the one outlined in this question's diagram: JPA. JoinTable and two JoinColumns, although with different issues.
I have three tables: Function, Group, and Location. Currently, I have a join table set up between Location and Group using #JoinTable. It is #ManyToMany on both sides, and works perfectly fine.
I am attempting to add the constraint that no Location should be associated with more than one Group that has the same Function. So I added a column for Function to my join table in my SQL schema and a uniqueness constraint across the Location and Function columns, like so:
create table function_table (
id varchar(50),
primary key(id)
);
create table group_table (
id varchar(50),
function_id varchar(50) not null,
primary key(id)
);
alter table group_table add constraint FK_TO_FUNCTION foreign key (function_id) references function_table;
create table location_table (
id varchar(50),
primary key(id)
);
create table group_location_join (
location_id varchar(50) not null,
group_id varchar(50) not null,
function_id varchar(50) not null,
primary key(location_id, group_id, function_id),
unique(location_id, function_id)
);
alter table group_location_join add constraint FK_TO_LOCATION foreign key (location_id) references location_table;
alter table group_location_join add constraint FK_TO_GROUP foreign key (group_id) references group_table;
alter table group_location_join add constraint FK_TO_FUNCTION foreign key (function_id) references function_table;
I then attempted to set up the following in my model entities:
#Entity
#Table(name = "function_table")
public class Function {
#Id
#Column(name = "id", length = 50)
private String id;
}
#Entity
#Table(name = "group_table")
public class Group {
#Id
#Column(name = "id", length = 50)
private String id;
#ManyToOne
#JoinColumn(name = "function_id", referencedColumnName = "id", nullable = false)
private Function function;
#ManyToMany
#JoinTable(name = "group_location_join",
joinColumns = {#JoinColumn(name = "group_id", referencedColumnName = "id"),
#JoinColumn(name = "function_id", referencedColumnName = "function_id")},
inverseJoinColumns = #JoinColumn(name="location_id", referencedColumnName = "id"))
private Set<Location> locations;
}
#Entity
#Table(name = "location_table")
public class Location {
#Id
#Column(name = "id", length = 50)
private String id;
#ManyToMany
#JoinTable(name = "group_location_join",
joinColumns = #JoinColumn(name="location_id", referencedColumnName = "id")
inverseJoinColumns = {#JoinColumn(name = "group_id", referencedColumnName = "id"),
#JoinColumn(name = "function_id", referencedColumnName = "function_id")})
private Set<Group> groups;
}
(Obviously, there is more to these entities, but I stripped them down to only the parts relevant to this question.)
This does not work. When I write a simple test to create a Location associated with a Group that is associated with a Function, the minute I try to flush the session to commit the transaction, Hibernate gives me this:
java.lang.ClassCastException: my.package.Group cannot be cast to java.io.Serializable
I think what's happening is that Hibernate is getting confused, throwing up its hands, and saying "I'll just serialize it, send it to the database, and hope it knows what's going on."
When I add implements Serializable and add a serialVersionUID to Group, I then get this:
org.hibernate.exception.SQLGrammarException: user lacks privilege or object not found: FUNCTION_ID
I'm not really sure how to proceed at this point, or if perhaps I have already proceeded too far down the wrong path. Maybe I'm not thinking about the SQL correctly, and there is a much easier way to ensure this constraint that doesn't involve all this ridiculousness.
Edit: In my system, the DAOs for the tables involved have no save capabilities. Which means that as long as my constraint is set up in the database, my application doesn't care; it can't insert things that violate the constraint because it can't insert things at all.
Edit 2: I never originally solved the stated problem, and instead simply added a third column in my database schema without touching the Java code, as stated in my first Edit section above. But I have since experimented with creating an explicit join table object with an #Embedded compound key, and it seems to work.

You are trying to create a composite primary key. In Hibernate you can do it using the #Embeddable annotation. In the example below you can find the way to use a composite key for two entities.
I believe you can move forward with this example and create your own version of primary key.
Mapping ManyToMany with composite Primary key and Annotation:

Persisting set of Enums in a many-to-many unidirectional mapping

I'm using Hibernate 3.5.2-FINAL with annotations to specify my persistence mappings. I'm struggling with modelling a relationship between an Application and a set of Platforms. Each application is available for a set of platforms.
From all the reading and searching I've done, I think I need to have the platform enum class be persisted as an Entity, and to have a join table to represent the many-to-many relationship. I want the relationship to be unidirectional at the object level, that is, I want to be able to get the list of platforms for a given application, but I don't need to find out the list of applications for a given platform.
Here are my simplified model classes:
#Entity
#Table(name = "TBL_PLATFORM")
public enum Platform {
Windows,
Mac,
Linux,
Other;
#Id
#GeneratedValue
#Column(name = "ID")
private Long id = null;
#Column(name = "NAME")
private String name;
private DevicePlatform() {
this.name = toString();
}
// Setters and getters for id and name...
}
#Entity
#Table(name = "TBL_APP")
public class Application extends AbstractEntity implements Serializable {
private static final long serialVersionUID = 1L;
#Column(name = "NAME")
protected String _name;
#ManyToMany(cascade = javax.persistence.CascadeType.ALL)
#Cascade({org.hibernate.annotations.CascadeType.SAVE_UPDATE})
#JoinTable(name = "TBL_APP_PLATFORM",
joinColumns = #JoinColumn(name = "APP_ID"),
inverseJoinColumns = #JoinColumn(name = "PLATFORM_ID"))
#ElementCollection(targetClass=Platform.class)
protected Set<Platform> _platforms;
// Setters and getters...
}
When I run the Hibernate hbm2ddl tool, I see the following (I'm using MySQL):
create table TBL_APP_PLATFORM (
APP_ID bigint not null,
PLATFORM_ID bigint not null,
primary key (APP_ID, PLATFORM_ID)
);
The appropriate foreign keys are also created from this table to the application table and platform table. So far so good.
One problem I'm running into is when I try to persist an application object:
Application newApp = new Application();
newApp.setName("The Test Application");
Set<DevicePlatform> platforms = EnumSet.of(Platform.Windows, Platform.Linux);
newApp.setPlatforms(platforms);
applicationDao.addApplication(newApp);
What I would like to happen is for the appropriate rows in the Platform table to created, i.e. create a row for Windows and Linux, if they don't already exist. Then, a row for the new application should be created, and then the mapping between the new application and the two platforms in the join table.
One issue I'm running into is getting the following runtime exception:
2010-06-30 13:18:09,382 6613126-0 ERROR FlushingEventListener Could not synchronize database state with session org.hibernate.TransientObjectException: object references an unsaved transient instance - save the transient instance before flushing: com.example.model.Platform
Somehow, the platform set is not being persisted when I try to persist the application. The cascade annotations are supposed to take care of that, but I don't know what's wrong.
So my questions are:
Is there a better way to model what I want to do, e.g. is using an Enum appropriate?
If my model is alright, how do I properly persist all of the objects?
I've been struggling with this for hours, and I've tried to recreate all of the code above, but it might not be complete and/or accurate. I'm hoping someone will point out something obvious!

You should decide whether your Platform is an entity or not.
If it's an entity, it can't be an enum, because list of possible platforms is stored in the database, not in the application. It should be a regular class with #Entity annotation and you will have a normal many-to-many relation.
If it isn't an entity, then you don't need TBL_PLATFORM table, and you don't have a many-to-many relation. In this case you can represent a set of Platforms either as an integer field with bit flags, or as a simple one-to-many relation. JPA 2.0 makes the latter case simple with #ElementCollection:
#ElementCollection(targetClass = Platform.class)
#CollectionTable(name = "TBL_APP_PLATFORM",
joinColumns = #JoinColumn(name = "APP_ID"))
#Column(name = "PLATFORM_ID")
protected Set<Platform> _platforms;
-
create table TBL_APP_PLATFORM (
APP_ID bigint not null,
PLATFORM_ID bigint not null, -- the ordinal number of enum value
primary key (APP_ID, PLATFORM_ID)
);
and enum Platform without annotations.

Simple use below mapping on your entity. Suppose that we have:
public enum TestEnum { A, B }
Then in your Entity class:
#ElementCollection(targetClass = TestEnum.class)
#CollectionTable(
name = "yourJoinTable",
joinColumns = #JoinColumn(name = "YourEntityId")
)
#Column(name = "EnumId")
private final Set<TestEnum> enumSet= new HashSet<>();

The following example shows what the situation is when Module is an entity and Langue is an enum.
#Entity
public class Module {
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
private Long id;
private String libelle;
#ElementCollection(targetClass = Langue.class, fetch = FetchType.EAGER)
#CollectionTable(name = "link_module_langue",
joinColumns = #JoinColumn(name = "module_id", referencedColumnName = "id"))
#Enumerated(EnumType.STRING)
#Column(name = "langue")
private Set<Langue> langues;
}
public enum Langue {
FRANCAIS, ANGLAIS, ESPAGNOLE
}
You should create link_module_langue table, please see the following sql code :
CREATE TABLE `link_module_langue` (
`module_id` BIGINT(20) NOT NULL,
`langue` VARCHAR(45) NOT NULL,
PRIMARY KEY (`module_id`, `langue`),
CONSTRAINT `module_fk`
FOREIGN KEY (`module_id`)
REFERENCES `module` (`id`)
ON DELETE CASCADE
ON UPDATE CASCADE);
NB: Langue is not an entity and would not have its own table.