Creating a query with a one-to-one relationship - spring-data-jpa

Question

I have two tables...a loan table and a customer table. A customer can make multiple loans but I would like to restrict the customer to one active loan at a time. They cannot create a second loan until the first loan is finished (loan.active=false)
I have set up my loan table like this :
#Entity
public class Loan implements Serializable {
private static final long serialVersionUID = 0x62B6DA99AA12AAA8L;
#Column #GeneratedValue(strategy = GenerationType.AUTO) #Id private Integer id;
#OneToOne(fetch = FetchType.LAZY)
private Customer customer;
#Column private String dateLoaned;
#Column private String dateToReturn;
#Column private String dateOfReturn;
#Column private Boolean active=false;
And the customer table like this :
#Entity
public class Customer implements Serializable {
private static final long serialVersionUID = 0x63A6DA99BC12A8A8L;
#Column #GeneratedValue(strategy = GenerationType.AUTO) #Id private Integer id;
#Column private String firstname;
#Column private String surname;
#Column private String address;
#Column private String town;
#Column private String postcode;
#Column (unique=true) private String personalnumber;
#Column (unique=true) private String emailaddress;
#OneToOne(fetch = FetchType.EAGER)
private Loan loan;
This allows me to create a new loan with the same customer. So far so good.
I would like to make a query that allows me to find if a customer already has an active loan.
My loan repository so far is :
#Query("select loan_id from Loan l where l.customer.id = :customerId and l.active = true")
Boolean customerHasActiveLoan(#Param("customerId") Integer customerId);
Is this the correct way to do this?

Answer 1

In spring-data-jpa you can both have #Query or write a method that generates a query. There is nothing wrong to have #Query but because your repository method is quite simple you can use also method name only
For the example the equivalent of:
//Will return the active loan, if exists, or null
#Query("select l from Loan l where l.customer.id = :customerId and l.active = true")
public Loan getActiveLoad(#Param("customerId") Integer customerId)
could be simplified as
public Local findOneByCustomerIdAndActiveIsTrue(Long id)
Sometimes method name approach can generate long method name, and for this reason, if you prefer, you can use #Query annotation