Temporal

Databases support temporal data types such as DATE (calendar date), TIME (clock time), and DATETIME (combined date and time).

Practice Exercise

MySQL also has TIMESTAMP, which is Unix Epoch time (seconds since 01/01/1970). DATETIME is by far the better choice.

Map these to the appropriate java.time classes such as LocalDate, LocalTime, and LocalDateTime.

  @Column(name="create_date")
  private LocalDateTime createDate; 

Practice Exercise

JPA 2.1 was released before Java 8, so it didn’t support java.time.LocalTime or java.time.LocalDate.

The spec for JPA 2.2 was released August 2017 and included support for the Java8 time API. Hibernate 5.3 included full integration of JPA 2.2.

Prior to this, all database temporal data had to be mapped to java.util.Date or its subclass java.sql.Date, java.util.Calendar, etc. and required you annotate java.util.Date or java.util.Calendar fields with the @Temporal annotation, and specify a value from the TemporalType enumeration.

• The value can be TIMESTAMP, TIME or DATE.

@Entity
@Table(name="CustomerTable")
public class Customer {
  @Id
  @GeneratedValue(strategy = GenerationType.IDENTITY)
  private int id;

  @Column(name="create_date")
  @Temporal(TemporalType.DATE)
  private Date createDate;

  // ...
}

While you may see this in legacy code, all new entities can use java.time classes without further annotations.

Testing Temporal Values

The java.time classes have getters you can use to test their content.

  @Test
  void test_Rental_temporal_mapping() {
    assertNotNull(rental);
    assertNotNull(rental.getRentalDate());
    assertEquals(2014, rental.getRentalDate().getYear());
    assertEquals(9, rental.getRentalDate().getMonthValue());
    assertEquals(24, rental.getRentalDate().getDayOfMonth());
  }

• getMonth() returns a special enumeration type Month, while getMonthValue() returns a 1 to 12 month number.

• Note that, while a month number might be displayed as 09, it's just the number 9; in Java a literal with a leading 0 is considered to be octal, for which the values 08 and 09 are invalid.

This far more reliable than testing with the toString() value:

    assertEquals("2014-09-24T22:04:30.0", rental.getRentalDate());

Practice Exercise

When using LocalDateTime, teammates in different time zones may run into "off-by-a-day" errors for times near midnight.

Drill

1. Add a new field called createdAt of type java.time.LocalDateTime to your Customer entity.

Here is the Customer for reference:

+-------------+----------------------+------+-----+-------------------+-----------------------------+
| Field       | Type                 | Null | Key | Default           | Extra                       |
+-------------+----------------------+------+-----+-------------------+-----------------------------+
| id          | int(10) unsigned     | NO   | PRI | NULL              | auto_increment              |
| store_id    | smallint(5) unsigned | NO   | MUL | NULL              |                             |
| first_name  | varchar(45)          | NO   |     | NULL              |                             |
| last_name   | varchar(45)          | NO   | MUL | NULL              |                             |
| email       | varchar(50)          | YES  |     | NULL              |                             |
| address_id  | int(10) unsigned     | NO   | MUL | NULL              |                             |
| active      | tinyint(1)           | NO   |     | 1                 |                             |
| create_date | datetime             | NO   |     | NULL              |                             |
| last_update | timestamp            | NO   |     | CURRENT_TIMESTAMP | on update CURRENT_TIMESTAMP |
+-------------+----------------------+------+-----+-------------------+-----------------------------+

• Don’t forget to add get/set methods.

• Write a test for the createdAt mapping.

• Look at your CustomerTest class. In each of your tests you are likely using the method em.find to retrieve a Customer entity - and likely the same Customer entity each time. This isn't very DRY... how could you refactor your test class to fix this?

• Look at how you are retrieving/assigning the EntityManagerFactory and EntityManager as fields at the class level... could you do something similar with the Customer entity?

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