Example test hibernate with H2

The main rule when testing hibernate

After adding the data and before you get this data for testing, you need to run the code:

session.flush();
session.clear();

• "Flush" - forcibly writes all entities to the database.
• "Clear" - (clear 1st level cache) Completely clear the session. Evict all loaded instances and cancel all pending saves, updates and deletions

Why is this so important? Since there may be cases when we have in the persistent state two objects with the same id

Example:

// 1. insert/create
User userCreated = getUserByDefault();
int idUserForUpdate = userRepository.createUser(userCreated);

// 2. flush and clear
flushAndClearSession();

// 3. get data and assert
User userExpected = UserUtil.createUserWithoutId("second", "second", "second", "123");
userExpected.setId(idUserForUpdate);
userRepository.updateUser(userExpected);

User actualUser = userRepository.getUser(idUserForUpdate);
assertThat(actualUser, equalTo(userExpected));

Without flushAndClearSession() will throw: org.hibernate.NonUniqueObjectException: A different object with the same identifier value was already associated with the session

Tests

When you run tests in the console, the display sql using lib "p6spy" - with params in sql:)

The log file test.log contains the sql requests generated using standard tools of hibernate.

Testing inheritance in Hibernate

No inheritance

This strategy is used if we want to share Java code between entity classes.
Use @MappedSuperclass in base class

see dir: /src/test/java/org/example/inheritance/no_inheritance

Single table

The Single Table strategy creates one table for each class hierarchy. This is also the default strategy chosen by JPA if we don’t specify one explicitly.

see dir: /src/test/java/org/example/inheritance/single_table

Table Per Class

The Table Per Class strategy maps each entity to its table which contains all the properties of the entity, including the ones inherited.
Like "No inheritance"

see dir: /src/test/java/org/example/inheritance/table_per_class

Joined

Using this strategy, each class in the hierarchy is mapped to its table.

see dir: /src/test/java/org/example/inheritance/joined

Testing relations in Hibernate

OneToMany by joinColumn

• Without cascade:
  see dir: /src/test/java/org/example/entity/relations/OneToMany/JoinColumn/NotCascade