HQL and Criteria

HQL (Hibernate Query Language)

Object-oriented query language, unlike SQL, the object names in HQL are case-sensitive (except for Java classes and other parts of the property are not case-sensitive); HQL is the object, not the table, and the polymorphism is supported; HQL is mainly operated by query. How query is created:

Queryq = Session.createquery (HQL);

L from person

L from user User Whereuser.name=:name

L from user user where User.name=:nameand User.birthday <: Birthday

Criteria

Criteria is a more object-oriented query method than HQL; How to create criteria:

Criteriacrit = Session.createcriteria (Domainclass.class);

Simple attribute conditions such as: Criteria.add (Restrictions.eq (Propertyname,value)),

Criteria.add (Restrictions.eqproperty (propertyname,otherpropertyname))

Different queries that take advantage of name

1, HQL

Session s=null;

Try {

S=hibernateutil. getsession ();

From Useruser an alias of user to user. Name represents the name of a property in a class

Fromobject is the row of records in all tables, from user to all record rows in the user's corresponding table

String querystring= "from user user where user.name=:n";//query string,hibernate Query Language hql. Class names are case sensitive

Query Query=s.createquery (queryString);//Generate a Query object to query

Query.setstring (0, name);//subscript starting from 0

Query.setstring ("n", name);//with named parameters, you don't need to index the subscript position.

Implementing paged Queries

Query.setfirstresult (0);//starting from line No. 0

Query.setmaxresults (2);//up to 2 records per page

/*query.list ();//List all result sets that meet the criteria

Query.uniqueresult ();//Returns a row of result sets */

If more than one record of the condition is met

List<user> list=query.list ();

for (User u:list) {

System. out. println (U.getid () + ":" +u.getname ());

}

If you know exactly what's on the line

/*useruser= (User) Query.uniqueresult ();

System.out.println (User.getid () + ":" +user.getname ()); */

}finally{

if (s!=null) {

S.close ();

}

}

2. Criteria

Session s=null;

Try {

S=hibernateutil. getsession ();

Criteria C=s.createcriteria (User. Class);//Check the table according to the mapping type

C.add (restrictions. EQ("name", name));//The constraint is added, the name attribute in user is equal to the parameter name

C.add (Restrictions.le ("Birthday", value));//birthday is less than or equal to ...

The above two sentences are equivalent to the criteria C=s.createcriteria (User.class). C.add (Restrictions.eq ("name", name));

List<user> list=c.list ();

for (User user:list) {

System. out. println (User.getid () + ":" +user.getname () + ":" +user.getbirthday ());

}

}finally{

if (s!=null) {

S.close ();

}

}

SQL is a table, HQL is the object, HQL supports polymorphism

HQL and Criteria