Hibernate Learning (vi) HQL

HQL Sentence Learning:

(1) Preliminary understanding of HQL

① HQL is the object-oriented query language, which uses the class name and the property name when querying,and theSql query uses the table name and the field name .

② Case Sensitive

③ Package Name: If the class name is not duplicated, do not write the package name, if the different packages have the same class, then you need to add a package name.

(2) hql Use

A. getting unique values

String hql= "SELECT COUNT (*) from Student";

Query q=session.createquery (HQL);

Number number= (number) Q.uniqueresult ();//Returns a piece of data

System.out.println (Number.intvalue ());

B. getting all the fields of a table

String sqlstring= "from Student";

Query query=session.createquery (sqlString);

List list=query.list ();

for (int i=0;i<list.size (); i++)

{

Student student= (Student) list.get (i);

System.out.println (Student.getname () + "ID:" +student.getid ());

}

C. returning a table section field

String hqlstring= "Select S.sno,s.name from Student S";

Query query=session.createquery (hqlstring);

List<object[]> list=query.list ();

for (int i=0;i<list.size (); i++)

{

Object[] Objects=list.get (i);

System.out.println (objects[0]+ "---" +objects[1]);

}

d. Two table connection queries (e.g., one-to-one relationship)

String hqlstring= "Select C.name,c.addressid.city,c.addressid.country from Companyxml C";

Query query=session.createquery (hqlstring);

List<object[]> list=query.list ();

for (int i=0;i<list.size (); i++)

{

Object[] Objects=list.get (i);

System.out.println (objects[0]+ "---" +objects[1]);

}

E. using map to encapsulate a row of records (alias, equivalent to a key name)

String hqlstring= "Select New Map (c.name as name,c.addressid.city as city,c.addressid.country as country) from Companyxml C ";

Query query=session.createquery (hqlstring);

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

for (int i=0;i<list.size (); i++)

{

Map Map=list.get (i);

System.out.println (Map.get ("name") + "---" +map.get ("City");

}

F. javabean encapsulation (get partial fields) can be encapsulated by a constructor function

String sqlstring= "Select New Student (S.sno,s.name,s.schoolname) from Student S";

Query query=session.createquery (sqlString);

List list=query.list ();

for (int i=0;i<list.size (); i++)

{

Student student= (Student) list.get (i);

System.out.println (Student.getname () + "ID:" +student.getschoolname ());

}

G. usage criteria query for the WHERE clause

String hqlteststring= "from Student s where s.name=? ";//Search by location, parameter index starting from 0

String hqlteststring= "from Student s where s.name=:name";//dynamic binding is bound by name

Query query=session.createquery (hqlteststring);

Query.setstring ("name", "Ytt");

List list=query.list ();

for (int i=0;i<list.size (); i++)

{

Student student= (Student) list.get (i);

System.out.println (Student.getname () + "ID:" +student.getschoolname ());

}

H. paging query

String sqlstring= "from Student";

Query query=session.createquery (sqlString);

Query.setfirstresult (0);//starting from the first few

Query.setmaxresults (10);//How many bars are displayed on a page

List list=query.list ();

for (int i=0;i<list.size (); i++)

{

Student student= (Student) list.get (i);

System.out.println (Student.getname () + "ID:" +student.getid ());

}

I. inner Connection, outer connection

String hqljoin= "Select S.name,b.picture from Student s, book B";//if using join will cause an exception

Query query=session.createquery (Hqljoin);

List<object[]> list=query.list ();

for (int i=0;i<list.size (); i++)

{

Object[] Object=list.get (i);

System.out.println (object[0]+ "--" +object[1]);

}

(3) Use of SQL statements

Native SQL (Use SQL statements directly in line and database, use sqlquery when querying)

String sqlstring= "Select S.sno,s.name from Student s where S.name=:name";

SQLQuery sqlquery=session.createsqlquery (sqlString);

Sqlquery.setstring ("name", "Ytt");

Sqlquery.addentity (Student.class);//equivalent to from Student, the result can be compared with the data in the Student table, directly through the JavaBean get the property can

List<object[]> list1=sqlquery.list ();

for (int i=0;i<list1.size (); i++)

{

Object[] Object=list1.get (i);

System.out.println (object[0]+ "--" +object[1]);

}

Hibernate Learning (vi) HQL