JPA Entity: direct reference to field … used in equals instead of getter

For fields with a mapping annotation like @OneToMany, @ManyToOne or @ManyToMany, you might run into this error:

JPA Entity: direct reference to field employee used in equals
  instead of getter getEmployee.

This error occurs when the field is used directly in equals or hashCode:

@ManyToOne
private Employee employee;

public boolean equals(Object other) {
    // ...
    return Objects.equals(employee, that.employee);
}

This is problematic, because the field employee might not be materialized yet. In other words, JPA may not have queried the employee yet and the reference could still be null. This might lead to incorrect results when calling equals or hashCode. JPA will materialize the field when the getter is called, but not when the field is referenced directly. Therefore, the field should always be referenced through its getter, in equals and hashCode:

public boolean equals(Object other) {
    // ...
    return Objects.equals(getEmployee(), that.getEmployee());
}

public int hashCode() {
    return Objects.hash(getEmployee());
}

If you have a reason, you can disable this check by suppressing Warning.JPA_GETTER. Also, EqualsVerifier assumes you use the JavaBeans convention to name your fields and getters. If you use a different convention, you can use #withFieldnameToGetterConverter() to override that.

See the manual page about JPA entities, specifically the section on Materialized fields, for more details.