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This article introduces the knowledge of "what is Mybaits caching mechanism". In the operation of actual cases, many people will encounter such a dilemma, so let the editor lead you to learn how to deal with these situations. I hope you can read it carefully and be able to achieve something!

1. First-level cache

Local cach

The data queried during the same session as the database will be placed in the local cache

If you need to get the same data later, take it directly from the cache

First-level caching is automatically turned on. Here are four ways to invalidate the first-level cache

1.sqlSession is different

The same 2.sqlSession, but different query conditions

3.sqlSession is the same, adding and deleting operations are performed during the query.

4. Manually cleared the first-level cache

1.1 first experience of first-level caching

@ Test

Public void test1 () throws Exception {

SqlSessionFactory sqlSessionFactory = getSqlSessionFactory ()

SqlSession openSession = sqlSessionFactory.openSession ()

EmployMapper mapper = openSession.getMapper (EmployMapper.class)

Employee id = mapper.getId (2)

System.out.println (id)

Employee id1 = mapper.getId (2)

System.out.println (id1)

OpenSession.close ()

}

Because there is a level of cache, there is no need to call sqlSession.

1.2 level 1 cache invalidation

SqlSession is different

@ Test

Public void test1 () throws Exception {

SqlSessionFactory sqlSessionFactory = getSqlSessionFactory ()

SqlSession openSession = sqlSessionFactory.openSession ()

EmployMapper mapper = openSession.getMapper (EmployMapper.class)

Employee id = mapper.getId (2)

System.out.println (id)

SqlSession openSession1 = sqlSessionFactory.openSession ()

EmployMapper mapper1 = openSession1.getMapper (EmployMapper.class)

Employee id1 = mapper1.getId (2)

System.out.println (id1)

OpenSession.close ()

}

Due to the difference of SqlSession

So that there is no cache

The same 2.sqlSession, but different query conditions

3.sqlSession is the same, adding and deleting operations are performed during the query.

4. Manually cleared the first-level cache

The openSession.clearCache () method is executed

two。 Second-level cache

Global caching

Is based on namespace-level caching, one namespace to one secondary cache

1. Query a piece of data and put it in the first-level cache

two。 If the session is closed, from level 1 to level 2, the new session information will refer to the level 2 cache.

3. Different namespace will be placed in different map and in different secondary cache.

2.1 enable second-tier cache

Turn on the secondary cache

Test.java

@ Test

Public void test2 () throws Exception {

SqlSessionFactory sqlSessionFactory = getSqlSessionFactory ()

SqlSession openSession = sqlSessionFactory.openSession ()

SqlSession openSession1 = sqlSessionFactory.openSession ()

EmployMapper mapper = openSession.getMapper (EmployMapper.class)

EmployMapper mapper1 = openSession1.getMapper (EmployMapper.class)

Employee id = mapper.getId (3)

System.out.println (id)

OpenSession.close ()

Employee id1 = mapper1.getId (3)

System.out.println (id1)

OpenSession1.close ()

}

Note that you need to close and get the second one, otherwise the secondary cache will not be turned on, because only when the session is closed will the primary cache be converted to the secondary cache.

2.2 attributes of secondary cache

CacheEnabled= "true"

Turn on the secondary cache

CacheEnabled= "false"

The secondary cache is turned off, but the primary cache is not closed

UseCache= "false"

The secondary cache cannot be used, but the primary cache can also be used

If flushCache= "true", both primary and secondary caches will be cleared.

Default is false

3. Cache schematic diagram

Cache query order:

Second-level cache

First-level cache

Database

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