CODEWITHSUNDEEP
javahibernatejpa
user1557654
user1557654

Reputation: 61

JPA multiple queries instead of one

I have two entities:

@Entity
@Table(name = "ACCOUNT")
@Cache(usage = CacheConcurrencyStrategy.READ_WRITE)
public class MyCloudAccount implements Serializable {

    ...

    @OneToMany(mappedBy = "account", cascade = CascadeType.ALL, fetch = FetchType.EAGER)
    private Set<ServerInstance> servers = new HashSet<ServerInstance>();

    ...
}

@Entity
@Table(name = "SERVER_INSTANCE")
public class ServerInstance implements Serializable {

    ...

    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "ACCOUNT_ID")
    private MyCloudAccount account;

    ...
}

I am getting all accounts by this code:

StringBuilder sql = new StringBuilder();
sql.append("SELECT e FROM ");
sql.append(persistentClass.getName());
sql.append(" e");
return entityManager.createQuery(sql.toString()).getResultList();

And this produces one query for the account and N queries for the servers instead of one with outer join. How to force JPA to make the query in optimal way?

Upvotes: 4

Views: 8513

Answers (1)

phoenix7360
phoenix7360

Reputation: 2907

I find it more convenient to use Java Persistence Query Language

you can do:

@NamedQueries{
    @NamedQuery(name="myQuery" query="SELECT a FROM MyCloudAccount JOIN FETCH a.servers")
}
public class MyCloudAccount{
    ...
}

then you can do

TypedQuery<MyCloudAccount> query = em.createNamedQuery("MyCloudAccount.myQuery", MyCloudAccount.class);
List<MyCloudAccount> results = query.getResultList();

EDIT You are actually already using JPQL. The key thing to your problem is using the JOIN FECTH command.

Upvotes: 2

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