Expose Association in Entity via Rest in Spring Boot - spring-boot

Question

I'm new in Spring Boot and a would like to add an association to the HTTP-Request.
Example:
// Transaction.java
#Entity
public class Transaction extends RepresentationModel<Transaction> {
// id;
#ManyToMany(cascade = CascadeType.ALL, fetch = FetchType.EAGER)
private List<Tag> tags;
}
// Tag.java
#Entity
public class Tag extends RepresentationModel<Transaction> {
// id;
// name..., and so on
}
Now I have two Repositories:
public interface TagRepository extends JpaRepository<Tag, Long> {
}
public interface TransactionRepository extends JpaRepository<Transaction, Long> {
}
When calling GET http://localhost:8080/transactions
I get:
{
"_embedded": {
"transactions": [
{
"date": "2021-01-01T01:01:11.000+00:00",
"and so on": "more fields" // but no "tags": [...]
"_links": {
"self": {"href": "http://localhost:8080/transactions/1"},
"tags": {"href": "http://localhost:8080/transactions/1/tags"}
}
}
]
},
"_links": {...},
"page": {...}
}
Is there any way to Modify the default Spring Endpoints to return an array of tags?
I would like to bypass create a custom Controller for this, because i need some parameters and filter methods.
The reason I need this function is, that I have a page which will load about 1k transactions and I don't want do make n+1 requests on GET /transactions/n/tags
Thanks for Help.

Answer 1

You need to add the join table annotation like this:
// Transaction.java
#Entity
public class Transaction extends RepresentationModel<Transaction> {
// id;
#ManyToMany(cascade = CascadeType.ALL, fetch = FetchType.EAGER)
#JoinTable(
name = "tag_transaction",
joinColumns = #JoinColumn(name = "transaction_id", referencedColumnName = "id"),
inverseJoinColumns = #JoinColumn(name = "tag_id", referencedColumnName = "id"))
private List<Tag> tags;
}
// Tag.java
#Entity
public class Tag extends RepresentationModel<Transaction> {
// id;
// name..., and so on
}