Some examples of Hibernate's HQL query

Hibernate is equipped with a very powerful query language, that is, HQL (Hibernate query Language), hql look like SQL, but just similar to the syntax structure, HQL is an object-oriented query, he can understand the concepts of inheritance, polymorphism.

HQL are case-sensitive, and SQL statement keywords (such as SELECT, From,where, and so on) are case insensitive.

Suppose we now have two tables, the book, and the Category:

Requirement 1: Query all titles in the Book Table:

Session session=hibernateutil.getsession (); // The list () method returns the result of the query // The type of the returned result is determined by the column of the query, where the Name property is queried, because the Name property is a string type, and all the resulting collection is a string type List<string> list=session.createquery ("Select name from book"). List ();  for (String s:list) {    System.out.println (s);}

Requirement 2: Query the Book table for all titles and authors (query multiple columns):

Method 1:

Session session=hibernateutil.getsession ();             // The list () method returns the    result of the query // A collection of arrays is returned when querying multiple properties, where name, and author are all string types, so the resulting list<object[]> list = Session.createquery ("Select Name,author from Book"). List ();  for (object[] o:list) {    System.out.println (o[0]+ "----" +o[1]);}    

Method 2:

1. In the book entity class, create a new constructor with the parameter name and author, (be careful not to forget the parameterless constructor);

2:

Session session=hibernateutil.getsession ();     // The list () method returns the result of the query and returns a collection of book types.
If you want to query all the book columns, the HQL statement is written directly as "from book". cannot be written as "select * from book".
Aliases can also be used in HQL statements, if aliases can also be written, "Select B from book B";
The following statement can also be writtenas follows: Select new Book (B.name,b.author) from book B;

list<book> list = Session.createquery ("Select New Book (Name,author) from book"

 for (book book:list) {System.out.println (book);}

Printing results are:

Book [Id=0, Name= Ding Lu Kee, price=0.0, Author= Jin Yong, pubdate=null, Category=null]
Book [Id=0, Name= Bucket, price=0.0, author= potatoes, pubdate=null, category=null]
Book [Id=0, Name= engulfing the stars, price=0.0, author= tomato, pubdate=null, category=null]
Book [Id=0, Name= Liang Jian, price=0.0, Author= Liang, Pubdate=null, Category=null]
Book [Id=0, Name= evil awe-inspiring, price=0.0, author=-eared, Pubdate=null, Category=null]

Requirement 3: Conditional query, query all book of 2<id<5:

Session session=hibernateutil.getsession ();     // The list () method returns the result of the query, which returns a collection     of book types // because the ID here is of type int, you can also write the Setparameter method as Setinteger, the first parameter: 0 for the first question mark list<book> list = Session.createquery ("From book where ID <? and ID;? "). Setparameter (0, 5). Setparameter (1, 2). List ();    for (book book:list) {         System.out.println (book);  }

Printing results are:

Book [id=3, Name= engulfing the stars, price=27.35, author= tomato, pubdate=2016-03-06 09:25:41.0, [email protected]
Book [id=4, Name= Liang Jian, price=42.35, Author= Liang, pubdate=2016-03-06 09:25:41.0, [email protected]

Requirement 4: Query all book with category "Fantasy class":

list<category> list = Session.createquery ("from Category where name =: Name"). Setparameter ("name", "Fantasy Class"). List (); Set<Book> books = list.get (0). Getbooks (); Iterator<Book> it =while (It.hasnext ()) {          System.out.println (It.next ());  }

Printing results are:

Book [id=2, Name= Bucket, price=22.35, author= potatoes, pubdate=2016-03-06 09:25:41.0, [email protected]
Book [id=3, Name= engulfing the stars, price=27.35, author= tomato, pubdate=2016-03-06 09:25:41.0, [email protected]

Demand 5: Paging query:

list<book> list = Session.createquery ("from book")                          . Setfirstresult (0)// start recording the following table ( currentPage-1) *pagesize)                           . Setmaxresults (3)// Set the number of records per page pageSize                            for  (book book:list) {         System.out.println (book);  }

Printing results are:

Book [Id=1, Name= Ding Lu Kee, price=12.35, Author= Jin Yong, pubdate=2016-03-06 09:25:41.0, [email protected]
Book [id=2, Name= Bucket, price=22.35, author= potatoes, pubdate=2016-03-06 09:25:41.0, [email protected]
Book [id=3, Name= engulfing the stars, price=27.35, author= tomato, pubdate=2016-03-06 09:25:41.0, [email protected]

If the parameter of Setfilrstresult () is changed to 3: It will be displayed:

Book [id=4, Name= Liang Jian, price=42.35, Author= Liang, pubdate=2016-03-06 09:25:41.0, [email protected]
Book [Id=5, Name= evil awe-inspiring, price=12.35, author=, pubdate=2016-03-06 09:25:41.0, [email protected]

Some examples of Hibernate's HQL query