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JPA Example

Examples prepared to explain the below concepts.

  1. Use Lazy loading

  2. Usage of java.time.localdate.

  3. Enum usage with converter

Lazy loading

Always advised to use lazy loading. Lazy loading fetches data only when it is really required. This example uses FetchType Lazy, the invited guests will be loaded only on demand.

A SELECT query applied for fetching booking or bookings will not fetch any invited guests. The below statement fetches all guests for a particular booking. It executes a SELECT query with booking id as arguement. BookingEntity.getInvitedGuests()

Enum

Using Converter annotation convert an entity attribute to a database value and vice versa. In this example, enum defined as BOOKED("B"), and NOTBOOKED("N") and CANCELED ("C"). This helps to make sure the code is not broken by refactorings.

The other two ways to deal with enums are by their Ordinal or by name. Ordinal may not be a good choice, if someone changes the places of the items in enum, wrong integer value may be stored.

LocalDateTime

java.time.LocalDateTime used instead of java.util.date, major benefits are:

  • LocalDateTime API has its own format/parse methods.

  • Addition/subtraction operation are easier (minusMinutes,plusDays etc.)