Query with a lot of fields and joins

I have to map a legacy database with tables that have a lot of fields and relations. For example (simplified code), 

@Entity @Table(name = "VISIT") public class VisitEntity {    @Id    private Integer Id;     @ManyToOne    @JoinColumn(name = "CD_COMPANY")    private CompanyEntity company;     @ManyToOne    @JoinColumn(name = "CD_EMPLOYEE")    private EmployeeEntity employee;     @ManyToOne    @JoinColumn(name = "CD_VISIT_TYPE")    private VisitTypeEntity visitType;     // A lot more fields and relations }

All other entityes used in the VisitEntity also have a lot of fields and more relations. For example, the EmployeeEntity is mapped as follows:

@Entity @Table(name = "EMPLOYEE") public class EmployeeEntity {    @Id    private Integer Id;     @Column(name = "EMP_NAME")    private String empName;     @ManyToOne    @JoinColumn(name = "CD_DEPARTMENT")    private DepartmentEntity department;     @ManyToOne    @JoinColumn(name = "CD_CITY")    private CityEntity city;     @ManyToOne    @JoinColumn(name = "CD_CATEGORY")    private CategoryEntity category;     // A lot more fields and relations }

With this classes, a simple find() in the VisitEntity will generate a query with more than 400 columns and more than 40 joins. I’m affraid that, in the future, this will represent a performance problem. I see two ways of reducing this number (assuming that when I use a VisitEntity I only need the field Id and name from the EmployeeEntity:

  1. Insted of using the find method of the entityManager use a TypedQuery referencing only a subset of the filed of the relation tables. For example:
SELECT v, e.id, e.empName, <more subsets from other tables> FROM VisitEntity v LEFT JOIN EmplooyEEEntity e WHERE v.id = :id

Even using query with a smaller list of fields, I think the JPA will have to create all the main entities.

  1. Use auxiliary entities. For example instead of unsing an EmployeeEntity I’ll create a VisitEmployeeEntity with the fields Id and Name only. This way, the find() method will query only the 2 fields of the EMPLOYEE table.

I appreciate more the second approach, even if it represent that I have to create more small classes.

Since I’m also new to the ORM world, what is your experience/opinon in this matter?