A brief talk on Hibernate--hibernate inquiry (query Language) (GO)

1. Querying Objects: Query has Org.hibernate.query and Javax.persistence.query,Use the following


If you search by criteria



2. Placeholder: such as the following example: Min and: Max, and Query.setparameter (Key,value);


Chained can also be, while here Setparameter ("", "") is automatically set the value of the parameter, if you know the incoming type can be setinteger.



3. Pagination Effect：
Remove records between M~n by Query.setmaxresult (n). Setfirstresult (M)

Setfirstresult (M): Choose to start from the first few lines, the default is Row0
Setmaxresult (n): Determines how many records to remove, by default all rows


Same as the following common QL statement implementation


4. Get Child properties
Query Query=session.createquery ("from score s where s.xxx.id= ...")


You can also take a temporary object out of it and put it in an object or a helper class that you build.
1.Query query=session.createquery ("Select S.name,c.name from Student s,course C where s.id=.. and c.id=. ")
2.Query query=session.createquery ("Select New Vobj (s.name,c.name) from Student s,course C where s.id=. and c.id=. ")

It is undesirable to take out some of the attributes that are encapsulated into a new object, preferably taking the entire attribute out to ensure the relevance of his logic；
If you want to remove it, take it.



5. Single Object Matching
If you know that the only object is taken out, then you do not need to query.list (), use Query.uniqueresult (); High efficiency



COUNT (*) returns a long type


Inch


Group by
Select AVG (s.age) from Student Group by S.col;

Having
Select COUNT (*) from Student s where group by S.col have Count (*) >3;
Null value empty: Below is the Student Class (Student) has set<course> courses attribute (Student selected course) Choose which courses are empty students


Like:% more; _ A


Distinct





6. The QL statements can be put together in order to maintain the modification with @namedqueries and @namedquery, when called with Session.getnamedquery (queryname)




7. Using the database's own language
If you can not solve the problem with HQL, then use the SQL language to solve, through Createsqlquery () to search the table, and Addentity (xx. Class) into an object


Of course, this can also be used with a named query



8. Bulk Delete: by Query.executequery (); return an int type, returns the number of successful rows for update and delete

A brief talk on Hibernate--hibernate inquiry (query Language) (GO)