Hibernate Usage Important Notes

Hibernate API introduction:
Configuration class

SessionFactory interface: It is best to create only one factory (unless it is a multi-data source)

Transaction interface

Query, Criteria interface: execute the database query, act as Hibernate querier

Hibernate commonly used identity generator
[quote]assigned

hilo

increment

identity

sequence

native[/quote]

* MySQL and SQL Server prioritize identity
* Oracle prioritizes the use of sequence
** If you want to improve the portability of your application, choose a native generator for cross-platform applications.

Conversion of three states:
Temporary objects, persistent objects and free objects

[img]http://dl.iteye.com/upload/attachment/149492/2306e85e-e491-34f2-a5df-df529e9a0f30.gif[/img]

Figure 1:


Important methods about Session:

beginTransaction();

close();

Connection () : **** This method directly obtains the JDBC connection, bypassing Hibernate to directly access the database, the addition, deletion, and generally will be more efficient than Hibernate.

delecte();

Get( Class entityClass,Serializable id); If there is no corresponding instance, it will return null

Load( Class entityClass,Serializable id);//If there is no corresponding instance, it will throw an exception.

save(Object entity);

update(Object entity)

saveOrUpdate(Object entity)

isInitialized() and initialize() ;/// can solve the problem of lazy loading better.

QBC query method: (Query By Criteria )
* Common methods in the Restrictions class to set query conditions
* Order class Order.asc ascending order, Order.desc descending
* Projections class Statistics and grouping results (Projections.avg,..)

//1
  Criteria criteria  = session.createCriteria(User.class);
  List list = criteria.list();

//2 pagination
  criteria.add(Restriction.eq("id",new Integer(1)));
  criteria.setMaxResults(10);
    User user = (User) criteria.uniqueResult()//Load a single object

  criteria.addOrder(Order.desc("id");)

//3 joint query
  Criteria cusCriteria = session.createCriteria(Customer.class);//
  Criteria ordCriteria = cusCriteria.createCriteria("orders");//
  ordCriteria.add(Restrictions.gt("money",new Double(1000)));
  ...

//4 offline query (bind to the session only when the query is executed) (usually used to dynamically build query statements)
    / / In the presentation layer constructs the query statement
  DetachedCriteria dCritera = DetachedCriteria.forClass(Order.class);
  dCritera.add(Restrictions.gt("money",new Double(1000)));
  ....
  serviec.queryOrders(dCritertia);

  Session session = ....
    //In the business layer
   Critertia criteria = dCritertia.getExecutable(session);
   criteria.list();

Bulk insert:
Method 1: Set hibernate.jdbc.batch_size to 50 (integer) and recommend to turn off the second level cache.

 for(int i=0;i<1000;i++){
  ....
  session.save(customer);
  if(i%50 ==0 ){
          Session.flush () ;/ / synchronize this batch of data with the database
          Session.clear () ;/ / clear the buffer area, release memory to attack a batch of use
  }
 }

Method 2: Bypassing Hibernate using JDBC


Batch update
Method 1: Configuration

<property name="hibernate.query.facotry_class">  
                        org.hibernate.hql.ast.ASTQueryTranslatorFactory
</property>

Method two.; use JDBC

batch deletion:


Multi-data source application:
....