CODEWITHSUNDEEP
hibernatejpa-2.0
Ram
Ram

Reputation: 2387

Why is Hibernate selecting same columns 4 times? Help with Mapping?

My classes look like these. Why does the same column get selected 4 times? What is problem with the mapping?

@Entity @Table(name="CLIENTS")
public class Client implements Serializable {

  @Id @GeneratedValue   @Column(name="GENERATED_ID")
  private Long id;

  @Column(name="NAME")
  private String name;

  @OneToMany(cascade=CascadeType.ALL, mappedBy="client", fetch=FetchType.EAGER)
  private Map<ParamPK, Param> params = new HashMap<ParamPK, Param>();
}

@Entity @Table(name="PARAMS")
public class Param implements Serializable {

  @EmbeddedId
  private ParamPK paramPK;

  @Column(name="VALUE")
  private String value;

  @ManyToOne @MapsId("clientId")
  private Client client;
}

@Embeddable
public class ParamPK implements Serializable {

  @Column(name="PARAM_KEY")
  private String key;

  @Column(name="CLIENT_GENERATED_ID")
  private Long clientId;
}

The queries generated by select gets same column 4 times.

/* from Client */ 
select
    client0_.GENERATED_ID as GENERATED1_1_,
    client0_.NAME as NAME1_ 
from
    CLIENTS client0_

/* load one-to-many Client.params */ 
select
    params0_.client_GENERATED_ID as client3_1_1_,
    params0_.client_GENERATED_ID as client3_1_,
    params0_.PARAM_KEY as PARAM1_1_,
    params0_.CLIENT_GENERATED_ID as CLIENT3_1_,
    params0_.client_GENERATED_ID as client3_0_0_,
    params0_.PARAM_KEY as PARAM1_0_0_,
    params0_.VALUE as VALUE0_0_ 
from
    PARAMS params0_ 
where
    params0_.client_GENERATED_ID=?

Note using Hibernate 3.5.3. Rest boilerplate code has been removed as irrelevant.

Upvotes: 4

Views: 694

Answers (1)

JB Nizet
JB Nizet

Reputation: 691635

You forgot to tell Hibernate what constitutes the key of the map of parameters. Add the following annotation to this map:

@OneToMany(cascade=CascadeType.ALL, mappedBy="client", fetch=FetchType.EAGER)
@MapKey(name = "paramPK")
private Map<ParamPK, Param> params = new HashMap<ParamPK, Param>();

This tells Hibernate that the paramPK property of the Param entity is the key of the map.

Upvotes: 3

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