Why is Hibernate searches the same column 4 times? Help 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 params = new HashMap();
}< br />
@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;
}

/* 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 params0_.
 params0_where 
 params0_.client_GENERATED_ID=?

My class looks like these. Why is the same column selected 4 times? What’s wrong 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 params = new HashMap();
}< br />
@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 query generated by select gets the 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 />ms0_ 
from
 PARAMS />ms0_ br /> params0_.client_GENERATED_ID=?

Note that using Hibernate 3.5.3. The remaining boilerplate code has been deleted as irrelevant.

You forgot to tell Hibernate what constitutes the key to the parameter map. Add the following comment to this map:

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

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