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Example 2 : POJO What is it? Example 3 : HIBERNATE Development process Example 4 : one-many How to configure Example 5 : many-one How to configure Example 6 : many-many How to configure Example 7 : get With load The difference between Example 8 : Common query 3 Two ways Example 9 : Three states Example 10 : openSession With getCurrentSession The difference between Example 11 : 1 Level cache Example 12 : 2 How to configure level cache
HIBERNATE It's a lightweight ORM Implementation of , Yes JDBC A package for .
ORM It means Mapping between objects and relational databases Object Relation Database Mapping.
POJO My full name is plain old java object
amount to JAVA BEAN, Also called entity class entity bean
One
complete hibernate Development process Include the following steps
1. to configure Hibernate.cfg.xml It contains database connection information , Which? HBM, Whether to use 2 Level cache , Show SQL, Dialects, etc 2. to configure hbm File Which class corresponds to which table , Property corresponds to what field , Various relationship mapping , For example ONE-MANY,MANY-ONE,MANY-MANY 3. use HIBNERATE Through Configuration Get SessionFactory, Then get it Session, Then carry out a series of database related business operations
With Category and Product One to many is an example
1. Category One of them set of products 2. stay Category.hbm.xml There must be a one to many mapping in <set name="products" lazy="false"> <key column="cid" not-null="false" /> <one-to-many class="Product" /> </set> Detailed reference Hibernate Realize one to many
Or with Product and Category take as an example
1. Product One of them category attribute 2. stay Product.hbm.xml In conduct many-to-one to configure <many-to-one name="category" class="Category" column="cid" /> Detailed reference Hibernate Realize many to one
With User and Product As an example
1. User There are products attribute 2. Product There are users attribute 3. Use the following to configure <set name="products" table="user_product" lazy="false"> <key column="uid" /> <many-to-many column="pid" class="Product" /> </set> For details, please refer to Hibernate Realize many to many
Through id obtain Product Objects have two ways , namely get and load
The difference between them is 1. Delayed loading 2. For id When it doesn't exist For details, please refer to Hibernate GET and LOAD The difference between
Entity class object in Hibernate There are 3 Kind of state
They are instantaneous , Persistence and disconnection instantaneous It means no and hibernate Any relationship , There is no corresponding record in the database , Once JVM end , The object disappears lasting It refers to an object and hibernate Contact , Have corresponding session, And there is a corresponding record in the database Off the pipe It refers to an object, although there is a corresponding record in the database , But it corresponds to session It's closed Code demonstration reference Hibernate Three states of objects instantaneous lasting Off the pipe
Hibernate There are two ways to get session, namely ：
OpenSession and getCurrentSession The difference between them is 1. Whether the obtained is the same session Object OpenSession Every time I get a new Session Object getCurrentSession In the same thread , Get the same... Every time Session Object , But what is obtained in different threads is different Session Object 2. The necessity of transaction submission openSession Only in increasing , Delete , Transactions are required when modifying , Not required for query getCurrentSession Yes, all operations must be carried out in a transaction , And after the transaction is committed ,session It turns off automatically , Can no longer be closed Code demonstration reference resources Hibernate OpenSession With GetCurrentSession The difference between
hibernate By default, the L1 cache is enabled , The L1 cache is stored in session Go ahead
Code demonstration reference What is? Hibernate L1 cache for
Hibernate The first level cache is Session Go ahead , L2 cache is in SessionFactory Go ahead
collocation method ： To be in hibernate.cfg.xml Middle opening <property name="hibernate.cache.use_second_level_cache">true</property> <property name="hibernate.cache.provider_class">org.hibernate.cache.EhCacheProvider</property> Example reference ： How Hibernate of ehcache L2 cache configuration
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