When JPA is used, the entity sub-generator can create relationships between entities.
Relationships only work when JPA is used. If you choose to use Cassandra or MongoDB, they won’t be available.
A relationship works between two entities, and JHipster will generate the code for:
As we use JPA, the usual one-to-many, many-to-one, many-to-many and one-to-one relationships are available:
Tip: the User
entity
Please note that the User
entity, which is handled by JHipster, is specific. You can do many-to-one
relationships to this entity (a Car
can have a many-to-one relationship to a User
). This will generate a specific query in your new entity repository, so you can filter your entity on the current security user, which is a common requirement.
Let’s start with two entities, a Owner
and a Car
. A owner can have many cars, and a car can have only one owner.
So this is a simple one-to-many relationship (one owner has many cars) on one side, and a many-to-one relationship (many cars have one owner) on the other side:
Owner (1) <-----> (*) Car
As the Car
table will need to have a foreign key on the Owner
table, we need to create the Owner
first. Here are the relevant JHipster questions for the Owner
:
yo jhipster:entity Owner
...
Generating relationships with other entities
? Do you want to add a relationship to another entity? Yes
? What is the name of the other entity? Car
? What is the name of the relationship? car
? What is the type of the relationship? one-to-many
? What is the name of this relationship in the other entity? owner
Please note that we selected the default options concerning the names of the relationships.
Now we can generate the Car
:
yo jhipster:entity Car
...
Generating relationships with other entities
? Do you want to add a relationship to another entity? Yes
? What is the name of the other entity? Owner
? What is the name of the relationship? owner
? What is the type of the relationship? many-to-one
? When you display this relationship with AngularJS, which field from 'Owner' do you want to use? id
That’s it, you now have a one-to-many relationship between those two entities!
In the previous example we had a bi-directionnal relationship: from a Car
instance you could find its owner, and from a Owner
instance you could get all of its cars.
A many-to-one uni-directional relationship means that the cars know their owner, but not the opposite.
Owner (1) <----- (*) Car
You would do that relationship for two reasons:
Owner
entity (as it won’t have to manage the collection of cars).In that case, you would still create the Owner
first, this time with no relationship:
yo jhipster:entity Owner
...
Generating relationships with other entities
? Do you want to add a relationship to another entity? No
And then the Car
entity, as in the previous example:
yo jhipster:entity Car
...
Generating relationships with other entities
? Do you want to add a relationship to another entity? Yes
? What is the name of the other entity? Owner
? What is the name of the relationship? owner
? What is the type of the relationship? many-to-one
? When you display this relationship with AngularJS, which field from 'Owner' do you want to use? id
This will work as in the previous example, but you won’t be able to add or remove cars from the Owner
entity.
A many-to-one uni-directional relationship means that the Owner
instance can get its collection of cars, but not the opposite. It is the opposite from the previous example.
Owner (1) -----> (*) Car
This type of relationship is not provided by default in JHipster at the moment, see #1569 for more information.
You have two solutions for this:
@OneToMany
annotationmvn liquibase:diff
to generate that table, see the documentation about using Liquibase diffA unidirectional one-to-one relationship means that the citizen
instance can get its passport, but the passport
instance can’t get to its owner.
Citizen (1) -----> (1) Passport
Generate the Passport
entity first, without any relationship to its owner:
yo jhipster:entity Passport
...
Generating relationships with other entities
? Do you want to add a relationship to another entity? No
Then, generate the Citizen
entity:
yo jhipster:entity Citizen
...
Generating relationships with other entities
? Do you want to add a relationship to another entity? Yes
? What is the name of the other entity? Passport
? What is the name of the relationship? passport
? What is the type of the relationship? one-to-one
? Is this entity the owner of the relationship? Yes
? What is the name of this relationship in the other entity? citizen
? When you display this relationship with AngularJS, which field from 'Passport' do you want to use? id
After doing this, a Citizen
possesses a passport, but no Citizen
instance is defined in Passport
.
For this example, a Person
can be the owner of many cars, and he can also be the driver of many cars:
Person (1) <---owns-----> (*) Car
Person (1) <---drives---> (*) Car
For this we need to use the relationship names, which we have left with their default values in the previous examples.
Generate the Person
entity, which has tow one-to-many relationships to the Car
entity:
yo jhipster:entity Person
...
Generating relationships with other entities
? Do you want to add a relationship to another entity? Yes
? What is the name of the other entity? Car
? What is the name of the relationship? ownedCar
? What is the type of the relationship? one-to-many
? What is the name of this relationship in the other entity? owner
...
Generating relationships with other entities
? Do you want to add a relationship to another entity? Yes
? What is the name of the other entity? Car
? What is the name of the relationship? drivedCar
? What is the type of the relationship? one-to-many
? What is the name of this relationship in the other entity? driver
Generate the Car
entity, which use the same relationship name has was configured in the Person
entity:
yo jhipster:entity Car
...
Generating relationships with other entities
? Do you want to add a relationship to another entity? Yes
? What is the name of the other entity? Person
? What is the name of the relationship? owner
? What is the type of the relationship? many-to-one
? When you display this relationship with AngularJS, which field from 'Person' do you want to use? id
...
Generating relationships with other entities
? Do you want to add a relationship to another entity? Yes
? What is the name of the other entity? Person
? What is the name of the relationship? driver
? What is the type of the relationship? many-to-one
? When you display this relationship with AngularJS, which field from 'Person' do you want to use? id
A Car
can now have a driver and a owner, which are both Person
entities.
A Driver
can drive many cars, but a Car
can also have many drivers.
Driver (*) <-----> (*) Car
At the database level, this means we will have a join table between the Driver
and the Car
tables.
For JPA, one of those two entities will need to manage the relationship: in our case, that would be the Car
entity, which will be responsible to add or remove drivers.
First generate the non-owning side of the relationship, the Driver
, with a many-to-many relationship:
yo jhipster:entity Driver
...
Generating relationships with other entities
? Do you want to add a relationship to another entity? Yes
? What is the name of the other entity? Car
? What is the name of the relationship? car
? What is the type of the relationship? many-to-many
? Is this entity the owner of the relationship? No
? What is the name of this relationship in the other entity? driver
Then generate the Car
, with the owning side of the many-to-many relationship:
yo jhipster:entity Car
...
Generating relationships with other entities
? Do you want to add a relationship to another entity? Yes
? What is the name of the other entity? Driver
? What is the name of the relationship? driver
? What is the type of the relationship? many-to-many
? Is this entity the owner of the relationship? Yes
? When you display this relationship with AngularJS, which field from 'Driver' do you want to use? id
In the user interface, you will be able to add/remove drivers from the Car
management page.
Following our example, a one-to-one relationship would mean that a Driver
can drive only one Car
, and a Car
can only have one Driver
.
Driver (1) <-----> (1) Car
First create the non-owning side of the relationship, in our case the Driver
:
yo jhipster:entity Driver
...
Generating relationships with other entities
? Do you want to add a relationship to another entity? Yes
? What is the name of the other entity? Car
? What is the name of the relationship? car
? What is the type of the relationship? one-to-one
? Is this entity the owner of the relationship? No
? What is the name of this relationship in the other entity? driver
Then generate the Car
, which owns the relationship:
yo jhipster:entity Car
...
Generating relationships with other entities
? Do you want to add a relationship to another entity? Yes
? What is the name of the other entity? Driver
? What is the name of the relationship? driver
? What is the type of the relationship? one-to-one
? Is this entity the owner of the relationship? Yes
? What is the name of this relationship in the other entity? car
? When you display this relationship with AngularJS, which field from 'Driver' do you want to use? id