Using Spring Query Methods JPA to efficiently query DB without multiple SELECT statements - spring

Question

I have an entity that has simple String columns as well as many ElementCollections (List and Map). I noticed looking at my postgres logs that PostGres when querying for this entity is doing a bunch of SELECT queries consecutively to get all the ElementCollections.
For efficiency, I would imagine doing one SELECT query with some inner JOINs might be better to avoid all of the individual SELECT queries. Is there a way to do that without writing a very verbose select query manually with all the INNER JOINs?
I have been looking around FetchTypes and Spring QueryData language, and DTO Projection but I imagine there might be a more straightforward way. The benefit I had been taking for granted is by explictly doing the JOINs if I add a new field then I will have to keep updating my query and if Spring is generating queries for me, then I wouldn't have to do anything.
// Person.java
#Entity
public Person {
#Id
long personId;
#Column
String firstName;
#Column
String lastName;
#ElementCollections
Set<String> someField;
#ElementCollections
Map<String, String> otherField;
#ElementCollections
Set<String> anotherField;
#ElementCollections
Map<String, String> yetAnotherField;
}
What is happening right now is
SELECT firstName, lastName FROM Person WHERE personId=$1
SELECT someField FROM Person_SomeField WHERE someField.personId=$1
SELECT otherField.key otherField.value FROM Person_OtherField WHERE otherField.personId=$1
And this continues for all of the ElementCollections tables which leads to a lot of queries.

Answer 1

Change your annotation to #ElementCollection(fetch = FetchType.EAGER).
It sounds like those fields are being lazily loaded (Hibernate is waiting until they are accessed to load them) which results in the N+1 queries you are seeing. LAZY loading is the default behavior for this type of member, which makes sense because loading it is not cheap. However, if you always want these members loaded, setting it to EAGER can make sense. Setting the fetch to EAGER will force Hibernate to load them along with the entity itself. This is the documentation for the fetch option on #ElementCollection:
(Optional) Whether the collection should be lazily loaded or must be
eagerly fetched. The EAGER strategy is a requirement on the
persistence provider runtime that the collection elements must be
eagerly fetched. The LAZY strategy is a hint to the persistence
provider runtime.