Personal study record: hibernate framework study notes (2) -----hibernate query method
1. Hibernate query classification:
The hibernate framework is a fully automated, object-oriented framework. Its query methods or statements can be divided into the following three types:
1. hql query: hibernate query language, which is a unique query language of the hibernate framework, providing richer, more flexible and more powerful query capabilities
2. Criteria query: Criteria is a completely object-oriented and extensible conditional query API. It is the core query object of the Hibernate framework that does not need to consider how the underlying database is implemented and how SQL statements are written.
3. Native sql query: It is inconvenient to use hql or criterion query for some complex query requirements, such as multi-table query, so a hibernate framework can still support native sql for query.
Second, the usage of three kinds of queries
1. hql query:
//The encapsulated hibernate tool class is used to obtain the session
public class HibernateUtils {
private static SessionFactory sf ;
static{
// get the configuration object
Configuration conf = new Configuration().configure();
//Get the session factory
sf = conf.buildSessionFactory();
}
public static Session openSession(){
//create new session
return sf.openSession();
}
public static Session getCurrentSession(){
//Get the session of the current thread
return sf.getCurrentSession();
}
}
public void fun1(){
Session session = HibernateUtils.openSession();
Transaction tr = session.beginTransaction();
//hql query
//-------------------------
//1, write hql statement
String hql = "from Customer";//------->Complete query
//2. Obtain the query object according to the statement
Query query = session.createQuery(hql);
//3. Obtain a collection or a single object according to the query object
List<Customer> list = query.list();
//-------------------------
tr.commit();
session.close();
for(Customer c : list){
System.out.println(c);
}
}
Note that the above hql specification statement should be select * from xx.xx.domain.Customer, and select * can be omitted for full query. If you want to query the number of rows in the table, you can use select count(*), and you cannot write the corresponding database table after from. Instead, you should write the complete persistent entity class name (object-oriented). If the entity class name is unique, the path can be omitted.
@Test
public void fun2(){
Session session = HibernateUtils.openSession();
Transaction tr = session.beginTransaction();
//hql query
//-------------------------
//1, write hql statement
String hql = "from Customer where cust_id = 3";//-------> conditional query
//2. Obtain the query object according to the statement
Query query = session.createQuery(hql);
//3. Obtain a collection or a single object according to the query object
Customer c = (Customer)query.uniqueResult();
//-------------------------
tr.commit();
session.close();
System.out.println(c);
}
@Test
public void fun3(){
Session session = HibernateUtils.openSession();
Transaction tr = session.beginTransaction();
//hql query
//-------------------------
//1, write hql statement
String hql = "from Customer where cust_id = ?";//-------> conditional query with placeholder
//2. Obtain the query object according to the statement
Query query = session.createQuery(hql);
//query.setLong (0, 3L);
// placeholder position and value
query.setParameter(0, 3L);
//3. Obtain a collection or a single object according to the query object
Customer c = (Customer)query.uniqueResult();
//-------------------------
tr.commit();
session.close();
System.out.println(c);
}
@Test
public void fun4(){
Session session = HibernateUtils.openSession();
Transaction tr = session.beginTransaction();
//hql query
//-------------------------
//1, write hql statement
String hql = "from Customer where cust_id = :cust_id";//-------> conditional query, with anonymous placeholder
//2. Obtain the query object according to the statement
Query query = session.createQuery(hql);
//query.setLong (0, 3L);
// placeholder position and value
query.setParameter("cust_id", 2L);
//3. Obtain a collection or a single object according to the query object
Customer c = (Customer)query.uniqueResult();
//-------------------------
tr.commit();
session.close();
System.out.println(c);
}
The above is a conditional query
@Test
public void fun5(){
//Paging query
Session session = HibernateUtils.openSession();
Transaction tr = session.beginTransaction();
//hql query
//-------------------------
//1, write hql statement
String hql = "from Customer";//------->Complete query
//2. Obtain the query object according to the statement
Query query = session.createQuery(hql);
query.setFirstResult(0);//---->limit 0,3
query.setMaxResults(3);
//3. Obtain a collection or a single object according to the query object
List<Customer> list = query.list();
//-------------------------
tr.commit();
session.close();
for(Customer c : list){
System.out.println(c);
}
}
The above is a pagination query
2. Criteria query:
/**
* criteria no statement query
*/
@Test
public void fun6(){
Session session = HibernateUtils.openSession();
Transaction tr = session.beginTransaction();
//--------------------
Criteria criteria = session.createCriteria(Customer.class);//----->Query all
List<Customer> list = criteria.list();
//--------------------
tr.commit();
session.close();
for(Customer c:list){
System.out.println(c);
}
}
criteria is completely object-oriented, it does not need to write any sql statement when querying, but calls its encapsulation method
Conditional query
Paging query
The total number of queries
3. Native sql query
There are two forms of basic query, one is to generate Object[] array collection, the other is to generate object collection, generally use the second
Conditional query is similar to hql query
Paging query
