Java - JPA @Basic and @Embedded annotations

Question

I am learning JPA from this tutorial.

I have some confusions in understanding the following annotations:

• @Basic
• @Embedded

Answer 1

@Basic

The Basic annotation can be applied to a persistent property or instance variable of any of the following types:

Java primitive types, wrappers of the primitive types, String, java.math.BigInteger, java.math.BigDecimal, java.util.Date, java.util.Calendar, java.sql.Date, java.sql.Time, java.sql.Timestamp, byte[], Byte[], char[], Character[], enums, and any other type that implements java.io.Serializable.

The use of the Basic annotation is optional for persistent fields and properties of these types. If the Basic annotation is not specified for such a field or property, the default values of the Basic annotation will apply.

Example:

@Basic
protected String name;

and

@Basic(fetch=LAZY)
protected String getName() { 
    return name; 
}

---

@Embedded

Specifies a persistent field or property of an entity whose value is an instance of an embeddable class. The embeddable class must be annotated as Embeddable.

Example 1:

@Embedded    
@AttributeOverrides({
       @AttributeOverride(name="startDate", column=@Column("EMP_START")),
       @AttributeOverride(name="endDate", column=@Column("EMP_END"))    
})        
public EmploymentPeriod getEmploymentPeriod() { ... }

Example 2:

@Entity
public class Project {
    @EmbeddedId ProjectId id;
    //other fields
}


@Embeddable
Class ProjectId {
    int departmentId;
    long projectId;
}

JSR Persistence Specification and Source reference