28-Transactions

Question 1

Propagations in Transactional

Answer 1

1. MANDATORY: throw an exception if no current txn
2. NESTED: create nested transaction if current txn exists, create new txn otherwise
3. NEVER: throws an exception if current txn exists
4. NOT_SUPPORTED: run without txn
5. REQUIRED: create new txn if not exist
6. REQUIRES_NEW: create new txn if not exist. Run in new independent txn otherwise
7. SUPPORTS: don’t create txn. Just use if exists

Question 2

Difference between Propagation.REQUIRED_NEW and Propagation.NESTED

Answer 2

REQUIRED_NEW: suspend current transaction, create a new transaction which won’t affect outer transaction if fails
NESTED: create a nested transaction if the current transaction exists. Failure in the nested transaction will roll back the current one.

Question 3

Isolations in Transactional

Answer 3

DEFAULT
READ_UNCOMMITTED
READ_COMMITTED
REPEATABLE_READ
SERIALIZABLE

Question 4

___means that none of the actions taken in a transaction violate any integrity constraints (e.g. foreign key constraint)

Answer 4

C in ACID

Question 5

Transaction APIs supported by Spring

Answer 5

JTA: java transaction API - distributed transaction
Hibernate
JPA
JDO

Question 6

What is D in ACID?

Answer 6

Committed changes are permanent

Question 7

Create JDBC transaction

Answer 7

conn = dataSource.getConnection()

conn. setAutoCommit(false)
conn. commit()
conn. rollback()

Question 8

Create JMS transaction

Answer 8

session = conn.createSession(true, 0)

session. commit()
session. rollback()

Question 9

Create JPA transaction

Answer 9

tx = entityManager.getTransaction()

tx. begin()
tx. commit()
tx. rollback()

Question 10

Create Hibernate transaction

Answer 10

tx = session.beginTransaction()

tx. commit()
tx. rollback()

Question 11

What is the difference between local and global transactions?

Answer 11

Local: single resource (e.g. db) & connection
Global: multiple resources (distributed transaction)

Question 12

What is the requirement for using JTA?

Answer 12

JTA implementation e.g.

1. Full application server (WebSphere, JBoss, WebLogic)
2. Standalone implementation (Atomikos, JTOM)

Question 13

What API does Spring use for the global and local transactions?

Answer 13

Use the same API

Question 14

What is the base interface that Spring uses to abstract transaction APIs?

Answer 14

PlatformTransactionManager

Question 15

Annotation to enable transaction in Spring. Where we should put it?

Answer 15

@EnableTransactionManager

Add it to a configuration class

Question 16

List down 6 implementations of PlatformTransactionManager?

Answer 16

1. DataSourceTransactionManager
2. JmsTransactionManager
3. JpaTransactionManager
4. JtaTransactionManager
5. WebLogicJtaTransactionManager
6. WebSphereUowTransactionManager

Question 17

Recommended bean name for transaction management bean?

Answer 17

transactionManager

Question 18

How to create a transaction manager from a data source?

Answer 18

new DataSourceTransactionManager(dataSource)

Question 19

Create a JTA transaction manager bean?

Answer 19

@Bean PlatformTransactionManager transactionManager() {
    return new JtaTransactionManager();
}

Question 20

Get the current transaction manually

Answer 20

DataSourceUtils.getConnection(dataSource);

Question 21

What happens if putting @Transactional to the interface?

Answer 21

Transaction will be applied for all methods

Question 22

What happens if putting @Transactional to the class?

Answer 22

1. Transaction will be applied for public methods only if it doesn’t implement an interface
2. Apply to all interface methods if it’s a bean of an interface. For this, putting annotation to class or interface takes the same effect

Question 23

Java’s @Transactional vs. Spring’s Transactional

Answer 23

1. Also supported by Spring but fewer options

2. Should use Spring’s Transactional instead

Question 24

What is the default for Transactional.propagation?

Answer 24

REQUIRED

Question 25

When does a transaction get rolled back?

Answer 25

When throwing RuntimeException e.g. DataAccessException, HibernateException, etc. or Error

Question 26

How to customize the rollback behavior?

Answer 26

@Transactional(rollbackFor=MyCheckedException.class, | noRollbackFor={JmxException.class, MailException.class})

Question 27

What happens if adding @Transactional to test methods/classes?

Answer 27

Transaction will be rolled back afterward | No need to clean up the database after testing

Question 28

How to persist data in 1 specific test method if its class is annotated with @Transactional?

Answer 28

``` Using @Commit for that method e.g. @Transactional class TestClass { @Test @Commit testMethod() {} } ```

Question 29

How to write transactional code manually?

Answer 29

``` return new TransactionTemplate(txManager).execute(status -> { try {} catch(SomeException e) { status.setRollbackOnly(); } }); ```

Question 30

When should use @Transactional(readOnly=true)?

Answer 30

To optimize performance if all queries inside are read, it will use 1 connection only.

Question 31

How to prevent modified data when reading?

Answer 31

@Transactional(readonly=true, isolation=REPEATABLE_READ) to prevent reading modified data until transaction commits

Question 32

In Spring test, how to run code before/after a transaction?

Answer 32

``` Using @BeforeTransaction e.g. class TestClass // run before and outside transaction @BeforeTransaction beforeTransaction() {} // run before and inside transaction @BeforeEach setup() {} @Test @Transactional void test() {} ```

Question 33

How to configure transaction with @Sql

Answer 33

Using @Sql(config=@SqlConfig(transactionMode=***))

Question 34

TransactionModes in @SqlConfig

Answer 34

1. ISOLATED: run @Sql script in a new transaction 2. INFERRED: get existing one or create new otherwise 3. DEFAULT: a. If it's set for method --> get from @SqlConfig in class level. Use INFERRED if there is no @SqlConfig in class level b. If it's set for class --> it's INFERRED

Question 35

Usage of @Primary

Answer 35

If there're multiple beans of the same type. The 1 with @Primary is the preference for @Autowired

Question 36

How to specify transaction manager in @Transactional if there's more than 1 txManager?

Answer 36

@Transactional("name-of-tx-manager") or | @Transactional(transactionManager="name-of-tx-manager")

Question 37

How global transaction works?

Answer 37

Two-phase commit

Question 38

How does @Sql work if not passing SQL file name?

Answer 38

Class level: ClassName.sql in the same package | Method level: ClassName.methodName.sql in the same package

Question 39

What are execution phases in @Sql?

Answer 39

@Sql(executionPhase=BEFORE_TEST_METHOD) | @Sql(executionPhase=AFTER_TEST_METHOD)

Question 40

How to config ErrorMode in @Sql

Answer 40

@Sql(config=@SqlConfig(errorMode=***))

Question 41

ErrorModes in @SqlConfig

Answer 41

1. DEFAULT: get from the parent (e.g. Class level), if not exist then FAIL_ON_ERROR 2. FAIL_ON_ERROR 3. CONTINUE_ON_ERROR 4. IGNORE_FAILED_DROPS: ignore all errors from "DROP IF EXISTS"

Question 42

What can we control with @SqlConfig?

Answer 42

1. errorMode 2. transactionMode 3. transactionManager: bean name 4. dataSource: bean name and some others

Question 43

Ways to run SQL scripts before each test?

Answer 43

1. Using @Sql 2. Create a bean of DataSourceInitializer a. Create ResourceDatabasePopulator b. ResourceDatabasePopulator.addScript("init.sql"); c. DataSourceInitializer. setDatabasePopulator(ResourceDatabasePopulator);

Question 44

Which of the following exceptions, when thrown, will cause a Spring transaction rollback by default?

Answer 44

If no custom rollback rules apply, the transaction will roll back on RuntimeException and Error but not on checked exceptions.