Question

I have a legacy database which can’t be changed because it’s hooked up to a 3rd party application.

One of the queries I’m working with for a new application looks like the following:

SELECT COL1, COL2, COL3, CODE1, CODE2,
(SELECT CODE_DESC FROM CODETABLE WHERE CODE_TYPE='A' CODE=INCIDENT.CODE1) AS CODE_DESC1,
(SELECT CODE_DESC FROM CODETABLE WHERE CODE_TYPE='B' CODE=INCIDENT.CODE2) AS CODE_DESC2
FROM INCIDENT
WHERE...

I’m trying to figure out how to translate that query into a set of Hibernate entities, but I’m a Hibernate newbie. I have 3 questions:

1. How do I join an entity to another entity in a one-to-one relationship multiple times? (the sub-queries)
2. How do I join an entity to another entity in a one-to-one relationship using a, for lack of a better word, parameter that has a fixed value (CODE_TYPE=’A’)?
3. Is it possible to do either of the above using annotations (because I like those)?

Here’s what I’ve tried thus far that didn’t work:

Object 1:

@Entity
@Table (name="Incident")
public class Incident {
    private String col1;
    private String col2;
    private String col3;
    private String code1;
    private String code2;
    private Code code_desc1;
    //private String code_desc2;
    /**
     * @param code_desc1 the code_desc1 to set
     */
    public void setCode_desc1(Code code_desc1) {
        this.code_desc1 = code_desc1;
    }
    /**
     * @return the code_desc1
     */
    @OneToOne
    @JoinTable(name="Codes",
            joinColumns=@JoinColumn(name="code1", referencedColumnName="CODE"),
            inverseJoinColumns=@JoinColumn(name="CODE_TYPE", referencedColumnName="'A'")
    )
    public Code getCode_desc1() {
        return code_desc1;
    }
// Rest of Getters & Setters...
}

Object 2:

@Entity
@Table (name="CODETABLE")
public class Codes {
    @Column(name="CODE_DESC") 
    private String codeDesc;
    @Column(name="CODE_TYPE")
    private String codeType;
    @Column(name="CODE")
    private String code;
// Getters & Setters
}

Basically, when I run the program, it complains about “A” not being a column name in the Codes entity.
Thanks for helping!

Answer 1

You should create a view as the query you described and define an entity mapping to this view.

If you still need the “Code” entity mapped at “Incident”, check following example:

@Entity
@Table(name="incident")
public class Incident {
    @Id
    @Column(name="id")
    private Integer id;

    @OneToOne
    @JoinColumn(name="code1")
    private CodeA typeACode;
    @OneToOne
    @JoinColumn(name="code2")
    private CodeB typeBCode;

    public Incident() {}

    public CodeA getTypeACode() { return this.typeACode; }
    public CodeB getTypeBCode() { return this.typeBCode; }
}

The “CodeA” is an entity mapping to a view, which comply with CODE_TYPE=’A’.
The “CodeB” is same as above recipe.