Hibernate Query Method (ii)

The 1.HQL query (Hibernate query Language) operates on entity classes and attributes

* Check all records

// The query object is used by the 1.HQL lookup operation //   (1) write the SQL statement to create the query object,    String hql = "from Student";    // From behind is the entity class name   Query query = session.createquery ("hql"); // (2) Call method to get results list<student> list = query.list (); // (3) traversing output  for (Student student:list) {  syso (Student.getid ()+ ":::" +student.getname ());}

2. Conditional query

*****1.

//The query object is used by the 1.HQL lookup operation//(1) write the SQL statement to create the query object,String hql = "from Student where id=? and name=? "; Query Query= Session.createquery ("HQL");//set a condition value//What is the first parameter? The position type is int the second parameter is the set valueQuery.setparameter (0,1); Query.setparameter (1, "Zhang San");//(3) Call method to get resultslist<student> list =query.list ();//(4) Traversing output for(Student student:list) {syso (Student.getid ()+":::"+student.getname ());}

2. Fuzzy condition Query

//The query object is used by the 1.HQL lookup operation//(1) write the SQL statement to create the query object,String HQL ="from Student where is name like?""; Query Query= Session.createquery ("HQL");//set a condition value//What is the first parameter? The position type is int the second parameter is the set value//query for names that begin with ZhangQuery.setparameter(0, "Zhang%");//(3) Call method to get resultslist<student> list =query.list ();//(4) Traversing output for(Student student:list) {syso (Student.getid ()+":::"+student.getname ());}

3. Sort Queries

// The query object is used by the 1.HQL lookup operation //   (1) write the SQL statement to create the query object, Ascending query ASC descending query desc;     ORDER BY CID ASC " ;      = Session.createquery ("hql"); // (3) Call method to get results list<student> list = query.list (); // (4) Traversing output  for (Student student:list) {  syso (Student.getid ()+ ":::" +student.getname ());}

4. Paging Query

implementing paging using the keyword limit in MySQL

SELECT * from Student  LIMIT 0,5//0 is the starting position 5 is the maximum number of records displayed

Two methods are encapsulated in hibernate to implement paged query operations

// The query object is used by the 1.HQL lookup operation //   (1) Write SQL statement query all create query object,    String hql = "from Student";      = Session.createquery ("hql"); //Set paging data query.setfirstresult (0); Query.setmaxresults (5); // (3) Call method to get results list<student> list = query.list (); // (4) Traversing output  for (Student student:list) {  syso (Student.getid ()+ ":::" +student.getname ());}

5. Projection Query

Query for all values of a field in a table

// The query object is used by the 1.HQL lookup operation //   (1) write the SQL statement to create the query object,    String hql = "Select  name from Student";      = Session.createquery ("hql"); // (3) Call the method to get the type of the result generic here can be a string if the type of multiple fields is not the same as can be written objectlist<object> list = query.list (); // (4) Traversing output  for (Object object:list) {  Syso (object);}

6. Aggregation function

Several common aggregation functions are count avg min Max sum;

Show the number of records in the query table here

// The query object is used by the 1.HQL lookup operation //   (1) write the SQL statement to create the query object,    String hql = "Select COUNT (*) from Student";      = Session.createquery ("hql"); // (3) Call method to get results here, using the Query object method directly returns the object form without a list Object obj =  query.uniqueresult (); SYSO (obj); <--Note that the above method return type is object if you want to return an int or other type  we first consider a strong turn of the type, but here we will output an exception  . The exception type is a type conversion exception (ClassCastException) so we will first convert the object type to a long type in the conversion to an integer type; long LongO = (long) obj; int count = Longo.intvalue (); Syso (count);  -

Hibernate Query Method (ii)