Property Annotation

The Property annotation is used to explicitly mark a field of an entity as a persistable field. By default, all fields of entity are treated as persistable, as long as they -

• have an accessor and a mutator method
• do not have @Ignore annotation

The Property annotation allows for the following customization:

• Define the name of the property to be used in the Google Cloud Datastore. If a property name is not set explicitly, the field name will be used as the property name.
• Control whether or not a property is to be indexed. By default, all properties are indexed.
• Specify the optionality - whether or not to store the property if the value is null. By default, a property is always stored into the Datastore, even if its value is null.

Example

Person.java

In the example below -

• Field firstName is mapped to a property named fname. In addition, first name is not indexed.
• Field lastName is mapped to a property named lname.
• Field birthDate is mapped to a property named dob (date of birth).
• Field ethnicity is marked as optional. This means, if ethnicity is null, the entity manager does not write the ethnicity property to the Cloud Datastore.

import java.time.LocalDate;

import com.jmethods.catatumbo.Entity;
import com.jmethods.catatumbo.Identifier;
import com.jmethods.catatumbo.Ignore;
import com.jmethods.catatumbo.Property;

@Entity
public class Person {
  @Identifier
  private long id;
  @Property(name = "fname", indexed = false)
  private String firstName;
  @Property(name = "lname")
  private String lastName;
  @Property(name = "dob")
  private LocalDate birthDate;
  @Ignore
  private int age;
  @Property(optional = true)
  private String ethnicity;

  public long getId() {
    return id;
  }

  public void setId(long id) {
    this.id = id;
  }

  public String getFirstName() {
    return firstName;
  }

  public void setFirstName(String firstName) {
    this.firstName = firstName;
  }

  public String getLastName() {
    return lastName;
  }

  public void setLastName(String lastName) {
    this.lastName = lastName;
  }

  public LocalDate getBirthDate() {
    return birthDate;
  }

  public void setBirthDate(LocalDate birthDate) {
    this.birthDate = birthDate;
  }

  public int getAge() {
    return age;
  }

  public void setAge(int age) {
    this.age = age;
  }

  public String getEthnicity() {
    return ethnicity;
  }

  public void setEthnicity(String ethnicity) {
    this.ethnicity = ethnicity;
  }

}

PersonDAO.java

import com.jmethods.catatumbo.EntityManager;
import com.jmethods.catatumbo.EntityManagerFactory;

public class PersonDAO {

  private static PersonDAO instance = new PersonDAO();
  private EntityManager em;

  public static PersonDAO getInstance() {
    return instance;
  }

  private PersonDAO() {
    em = EntityManagerFactory.getInstance().createDefaultEntityManager();
  }

  public Person create(Person person) {
    return em.insert(person);
  }

  public Person update(Person person) {
    return em.update(person);
  }

  public void delete(Person person) {
    em.delete(person);
  }

  public Person read(long id) {
    return em.load(Person.class, id);
  }

}

CreatePerson.java

import java.time.LocalDate;

import com.jmethods.catatumbo.EntityManagerException;

public class CreatePerson {

  public static void main(String[] args) {
    Person person = new Person();
    person.setFirstName("John");
    person.setLastName("Doe");
    person.setBirthDate(LocalDate.of(1990, 2, 15));
    try {
      PersonDAO dao = PersonDAO.getInstance();
      person = dao.create(person);
      System.out.printf("Person entity with ID %d was created successfully", person.getId());
    } catch (EntityManagerException e) {
      e.printStackTrace();
    }
  }

}

The screenshot below illustrates the Person entity created in the Cloud Datastore:

Note that -

• Property names are not the same as field names, instead they are the names specified in the Property annotation.
• Column heading fname is grayed out to indicate that the fname property is not indexed
• The property ethnicity does not exist because ethnicity is null