CODEWITHSUNDEEP
javaspringhibernatejpa
Ruslan Akhundov
Ruslan Akhundov

Reputation: 2216

Using JPA join via one column and return another one

I have table with two columns:

@Entity
@Table(name = "documents")
public class Document {
    @Id
    @Column(name = "key")
    public String key;
    @Lob
    @Column(name = "value")
    public byte[] value;
    ....some more data...
}

And I have another table, with some field where I have a reference to the Document table, via key column reference:

@Entity
@Table(name = "table")
public class Table {
     ...some values and id...
     @Nullable
     @ManyToOne(fetch = FetchType.LAZY, targetEntity = Document.class)
     @JoinColumn(name = "some_document_id", referencedColumnName = "key",
             foreignKey = @ForeignKey(name = "document_id_fk"))
     @Convert(converter = ByteArrayToStringConverter.class)
     public String documentValue; //join documents by key column and return value column
}

What I want, is to fetch not the whole Document with all fields when joining it from this table, but to fetch only one column named value, and then convert it from byte[] to String.

I understand that I can just call getter from java code, but I am curious if that is possible by Jpa/Hibernate API?

Upvotes: 2

Views: 2245

Answers (1)

CIPHER007
CIPHER007

Reputation: 376

You can create a method in your repository with @Query annotation like below code

@Repository
public interface TableRepository extends JpaRepository<User, Serializable>{

       @Query("select d.value from Table t LEFT JOIN t.documentValue d where d.key=:key")
       byte[] findValue(@Param("key") String key);
}

This method will return you a byte[] array that you can easily convert in String using String s = new String(byteArray)

Upvotes: 1

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