JPA supports three types of inheritance, In this article will try
"single table inheritance using EJB datacontrol". For more information on JPA inheritance go through the
link.
In single table inheritance, a single table is used to store all of the instances of the entire inheritance hierarchy. The table will have a column for every attribute of every class in the hierarchy. A discriminator column is used to determine which class the particular row belongs to, each class in the hierarchy defines its own unique discriminator value.
Table Structure: -
Model Diagram:-
In the above example the discriminator column (SEX) is added to the table to distinguish between the Men and Women instances.
You can
download the sample workspace from here
[Runs with Oracle JDeveloper 11.1.2.2.0 + HR Schema]
Note: - You can find the sql file in application JPASingleTableApp/etc/ folder
Implementation Steps:-
Lets create a Fusion Web Application with Entities based on Person, edit the Person.java entity and remove the menAttr, womenAttr attributes. Add the below annotation in Person entity.
@Table(name="PERSON")
@Inheritance(strategy=InheritanceType.SINGLE_TABLE)
@DiscriminatorColumn(name="SEX", discriminatorType=DiscriminatorType.STRING,length=1)
Create an entity Men by extending the Person and add the below code.
@Entity
@Table(name = "PERSON")
@DiscriminatorValue("M")
@NamedQueries( { @NamedQuery(name = "Men.findAll", query = "select o from Men o") })
public class Men extends Person implements Serializable {
@Column(name = "MEN_ATTR")
private String menAttr;
public Men() {
}
public String getMenAttr() {
return menAttr;
}
public void setMenAttr(String menAttr) {
this.menAttr = menAttr;
}
}
Create an entity Women by extending the Person and add the below code.
@Entity
@Table(name = "PERSON")
@DiscriminatorValue("W")
@NamedQueries( { @NamedQuery(name = "Women.findAll", query = "select o from Women o") })
public class Women extends Person implements Serializable {
@Column(name = "WOMEN_ATTR")
private String womenAttr;
public Women() {
}
public String getWomenAttr() {
return womenAttr;
}
public void setWomenAttr(String womenAttr) {
this.womenAttr = womenAttr;
}
}
Next create a Session Bean and data control for the Session Bean and in ViewController project create a jspx page and drop menFindAll, womenFindAll as separate Table->ADF Read only Table. Run the jspx page and web page will be displayed as shown in below image, table bound to menFindAll should display only men records and table bound to womenFindAll should display only women records.
