Show only object id in OneToMany List - spring

Question

I have these two classes:
Quota Class
#Entity
#Data
#EqualsAndHashCode(callSuper=false)
#Table(name="quotas")
#Relation(collectionRelation = "quotas", itemRelation = "quota")
#JsonIdentityInfo(generator = ObjectIdGenerators.PropertyGenerator.class, property = "id")
public class Quota extends RepresentationModel<Quota> {
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
private int id;
#OneToMany(fetch = FetchType.LAZY, mappedBy = "quota")
#JsonIdentityReference(alwaysAsId = true)
private List<Customer> customers;
private String type;
private boolean flatrate;
#CreatedDate
private long createdDate;
#LastModifiedDate
private long lastModifiedDate;
And Customer:
#Entity
#Data
#EqualsAndHashCode(callSuper=false)
#Table(name = "customers")
#Relation(collectionRelation = "customers", itemRelation = "customer")
#JsonIdentityInfo(generator = ObjectIdGenerators.PropertyGenerator.class, property = "id")
public class Customer extends RepresentationModel<Customer> {
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
private int id;
private String name;
private String customerNumber;
#CreatedDate
private long createdDate;
#LastModifiedDate
private long lastModifiedDate;
#ManyToOne
#JoinColumn(name = "quota_id", referencedColumnName = "id")
#JsonProperty("quotaId")
#JsonIdentityReference(alwaysAsId = true)
private Quota quota;
}
What i get when i make a GET request on all Customers:
{
"_embedded": {
"customers": [
{
"id": 3,
"name": "Customer Test3",
"customerNumber": "45678",
"createdDate": 1596117132045,
"lastModifiedDate": 1596117132045,
"_links": {
"self": {
"href": "http://localhost:2502/seminars/3"
}
},
"quotaId": 1
},
{
"id": 1,
"name": "test3",
"customerNumber": "12345",
"createdDate": 1596111304535,
"lastModifiedDate": 1596186450456,
"_links": {
"self": {
"href": "http://localhost:2502/seminars/1"
}
},
"quotaId": 1
},
{
"id": 2,
"name": "Customer Test2",
"customerNumber": "23456",
"createdDate": 1596112131934,
"lastModifiedDate": 1596112131934,
"_links": {
"self": {
"href": "http://localhost:2502/seminars/2"
}
},
"quotaId": 2
},
{
"id": 4,
"name": "Customer Test4",
"customerNumber": "34567",
"createdDate": 1596117145795,
"lastModifiedDate": 1596117145795,
"_links": {
"self": {
"href": "http://localhost:2502/seminars/4"
}
},
"quotaId": 2
},
{
"id": 6,
"name": "Customer Test6",
"customerNumber": "12345",
"createdDate": 1596187250598,
"lastModifiedDate": 1596187250598,
"_links": {
"self": {
"href": "http://localhost:2502/seminars/6"
}
},
"quotaId": null
}
]
},
"_links": {
"self": {
"href": "http://localhost:2502/seminars?page=0&size=20&sort=quota,asc"
}
},
"page": {
"size": 20,
"totalElements": 5,
"totalPages": 1,
"number": 0
}
}
What i get when i make a GET request in all Quotas:
{
"_embedded": {
"quotas": [
{
"id": 1,
"customers": [
{
"id": 3,
"name": "Customer Test3",
"customerNumber": "45678",
"createdDate": 1596117132045,
"lastModifiedDate": 1596117132045,
"quotaId": 1
},
{
"id": 1,
"name": "test3",
"customerNumber": "12345",
"createdDate": 1596111304535,
"lastModifiedDate": 1596186450456,
"quotaId": 1
}
],
"type": "paid",
"createdDate": 1596111304535,
"lastModifiedDate": 1596111304535,
"flatrate": true,
"_links": {
"self": {
"href": "http://localhost:2502/quotas/1"
}
}
},
{
"id": 2,
"customers": [
{
"id": 2,
"name": "Customer Test2",
"customerNumber": "23456",
"createdDate": 1596112131934,
"lastModifiedDate": 1596112131934,
"quotaId": 2
},
{
"id": 4,
"name": "Customer Test4",
"customerNumber": "34567",
"createdDate": 1596117145795,
"lastModifiedDate": 1596117145795,
"quotaId": 2
}
],
"type": "demo",
"createdDate": 1596111304535,
"lastModifiedDate": 1596111304535,
"flatrate": true,
"_links": {
"self": {
"href": "http://localhost:2502/quotas/2"
}
}
}
]
},
"_links": {
"self": {
"href": "http://localhost:2502/quotas?page=0&size=10&sort=id,asc"
}
},
"page": {
"size": 10,
"totalElements": 2,
"totalPages": 1,
"number": 0
}
}
I am happy with the result from Customers, but the result from quotas i would want to look like this:
{
"_embedded": {
"quotas": [
{
"id": 1,
"customers": [3,1],
"type": "paid",
"createdDate": 1596111304535,
"lastModifiedDate": 1596111304535,
"flatrate": true,
"_links": {
"self": {
"href": "http://localhost:2502/quotas/1"
}
}
},
{
"id": 2,
"customers": [2,4],
"type": "demo",
"createdDate": 1596111304535,
"lastModifiedDate": 1596111304535,
"flatrate": true,
"_links": {
"self": {
"href": "http://localhost:2502/quotas/2"
}
}
}
]
},
"_links": {
"self": {
"href": "http://localhost:2502/quotas?page=0&size=10&sort=id,asc"
}
},
"page": {
"size": 10,
"totalElements": 2,
"totalPages": 1,
"number": 0
}
}
For json serialization i use 'com.fasterxml.jackson.annotation.*'
I already tried it with using the #JsonBackRefference, #JsonIgnore, #JsonIngoreProperties and #JsonIdentityReference annotations but never got the wanted result.

Answer 1

I would recommend you introduce DTOs to model this rather than trying to annotate the entity classes with JSON annotations. At some point you will probably have conflicting needs i.e. one use case needs a field and another doesn't and then you will have to think about abstracting this anyway.
Having said that, this is a perfect use case for Blaze-Persistence Entity Views.
Blaze-Persistence is a query builder on top of JPA which supports many of the advanced DBMS features on top of the JPA model. I created Entity Views on top of it to allow easy mapping between JPA models and custom interface defined models, something like Spring Data Projections on steroids. The idea is that you define your target structure the way you like and map attributes(getters) via JPQL expressions to the entity model. Since the attribute name is used as default mapping, you mostly don't need explicit mappings as 80% of the use cases is to have DTOs that are a subset of the entity model.
A DTO mapping for your model could look as simple as the following
#EntityView(Quota.class)
public abstract class QuotaDto extends RepresentationModel<QuotaDto> {
public abstract Integer getId();
#Mapping("customers.id")
public abstract List<Integer> getCustomers();
public abstract String getType();
public abstract boolean isFlatrate();
public abstract long getCreatedDate();
public abstract long getLastModifiedDate();
}
#EntityView(Customer.class)
public abstract class CustomerDto extends RepresentationModel<CustomerDto> {
public abstract Integer getId();
public abstract String getName();
public abstract String getCustomerNumber();
public abstract long getCreatedDate();
public abstract long getLastModifiedDate();
#Mapping("quota.id")
public abstract Integer getQuotaId();
}
Querying is a matter of applying the entity view to a query, the simplest being just a query by id.
CustomerDto dto = entityViewManager.find(entityManager, CustomerDto.class, id);
But the Spring Data integration allows you to use it almost like Spring Data Projections: https://persistence.blazebit.com/documentation/entity-view/manual/en_US/index.html#spring-data-features
You are in control of the structure and can map anything to the properties. It will only fetch the mappings that you tell it to fetch.