JPA: create constraint between primary key column in one table and a non-primary column in another? - jpa

Question

I’m using JPA and trying to figure out how to create a unique constraint between a primary key column in one table and a non-primary key column in another. I have two tables:
Customer (
id character varying(32) NOT NULL,
customer_name character varying(50)
)
and
Account (
id character varying(32) NOT NULL,
account_name character varying(50)
)
There is a unidirectional, one-to-many relationship between Customer and Account with a constraint that Account.account_name is unique per Customer. The code looks like so:
#Entity
public class Customer {
#Id
#Column(length=32)
private String id;
#Column(unique=true, length=50)
private String customer_name;
#OneToMany
private List<Account> accounts;
...
}
and
#Entity
public class Account {
#Id
#Column(length=32)
private String id;
#Column(length=50)
private String account_name;
...
}
A join table is created by default:
CUSTOMER_ACCOUNTS (
customer_id character varying(32),
accounts_id character varying(32)
)
How do I create the unique constraint to ensure an Account.account_name is unique per Customer?

Answer 1

Add a JoinColumn annotation to the Customer class::
#Entity
public class Customer {
#Id
#Column(length=32)
private String id;
#Column(unique=true, length=50)
private String customer_name;
#OneToMany(mappedBy="customer")
#JoinColumn(name="CUSTOMER_ID", referencedColumnName="ID")
private List<Account> accounts;
...
}
Referenced column name points to the primary key of the Customer table, while name points to the foreign key field of the Account table.
You should also add a CUSTOMER_ID field and a composite unique constraint to the account entity:
#Entity
#Table(
uniqueConstraints=
#UniqueConstraint(columnNames={"CUSTOMER_ID", "ACCOUNT_NAME"})
)
public class Account {
#Id
#Column(length=32)
private String id;
#Column(length=50)
private String account_name;
#Column(name="CUSTOMER_ID")
private String customer_id;
...
}