java - Spring 查询在整个对象上不同

Question

我正在使用 spring 数据并进行了以下查询:

@Query("SELECT DISTINCT u.pk.fleet.fleetName FROM FleetHasUser u WHERE u.pk.user.username = ?1")
List<FleetName> allFleetNameForUser(String username);

此查询的目的是查找特定用户的所有 FleetName。这是感兴趣的数据库模式的一部分:

FleetHasUser 类:

@Entity
@Table(name = "fleet_has_user", catalog = "dart")
@AssociationOverrides({
    @AssociationOverride(name = "pk.user", 
        joinColumns = @JoinColumn(name = "id_username")),
    @AssociationOverride(name = "pk.fleet", 
        joinColumns = @JoinColumn(name = "id_fleet")) })
public class FleetHasUser implements java.io.Serializable {

    /**
     * 
     */
    private static final long serialVersionUID = 1L;
    private FleetHasUserKeys pk = new FleetHasUserKeys();
    
    
    @EmbeddedId
    public FleetHasUserKeys getPk() {
        return pk;
    }

FleetHasUserKeys 类:

@Embeddable
public class FleetHasUserKeys implements Serializable {
    
    private static final long serialVersionUID = 1L;
    protected User user;
    protected Fleet fleet;

舰队类:

@Entity
@Table(name = "fleet", catalog = "dart")
public class Fleet implements java.io.Serializable {

    /**
     * 
     */
    private static final long serialVersionUID = 1L;
    private Integer idFleet;
    private Ecu ecu;
    private String application;
    private Cubic cubic;
    private Integer power;
    private String euroClass;
    private String engineType;
    private Traction traction;
    private String transmission;
    private String note;
    private FleetName fleetName;
    @JsonIgnore
    private Set<Car> cars = new HashSet<Car>(0);
    @JsonIgnore
    private Set<FleetHasUser> fleetHasUsers = new HashSet<FleetHasUser>(0);

如您所见，FleetName 是一个类。我尝试不使用 distinct 并且列表中有重复的元素，因此在创建子查询之前我插入了 distinct 仅用于测试并且它有效。我没有在谷歌上找到信息，但是可以在对象上使用 distinct 吗？它是如何工作的(检查主键字段)？

也许我什至可以创建一个像 findDistinctPkFleetFleetNameByPkUserUsername 这样的 Spring 数据查询？谢谢

Answer 1

据我所知，distinct 应用于查询而不是映射阶段，如您所见@Query doc注释仅执行 jpql 查询，因此 native 不同。

正如您所说，执行不同的其他选项是 Spring data Distinct

您不能将“Distinct”应用于对象，但您可以映射到 Set 上以避免重复，但更好的方法是正确过滤数据库中的数据。