Hibernate Chapter 2: Association ing

Document directory

• 1. Copying-to-one
• 2. ont-to-memory

1. Copying-to-one

I was going to write it, but I can only write one-to-one, one-to-one, and one-to-one. Sorry.

In chapter 1, we have a perceptual knowledge of hibernate. Understand the lifecycle of an object.

Http://blog.csdn.net/wiksys/article/details/7934380

In this chapter, we will learn the associations between objects.

First, recall. How do we deal with associations in the database? The foreign key )! By the way, it is the foreign key. So how can we establish a relationship between the object-oriented model and the database relational model? With this problem in mind, let's start this chapter.

Before learning associations, let's first understand the relationships between entities?

Association: Implemented by an instance where one object holds another object

Generalized relationship: this is achieved through inheritance between objects.

Small experience: Association is an important feature of object relationship ing, but it may cause lower performance. So pay attention to the design.

 

Direction-to-one: one-to-many Association

 

Case: Students and dormitories

One dormitory for multiple students: Multiple to one.

Class Diagram

 

We practice inserting a dormitory record into the table and then adding a student record to the dormitory record.

SQL script

create table dorm(    id number primary key,    name varchar2(20) not null);Create table student(    id number primary key,    dorm_id number,    name varchar2(20) not null,    foreign key(dorm_id) references dorm(id));create sequence hibernate_sequence start with 1;insert into dorm values(hibernate_sequence.nextval,'101');insert into dorm values(hibernate_sequence.nextval,'102');insert into student values(hibernate_sequence.nextval,21,'wiksys');commit;

Entity class: dormitory :( dorm. Java)

Package Org. wiksys. chap02.bean;/*** dormitory table * @ author wiksys **/public class dorm implements Java. io. serializable {private long ID; private string name; public long GETID () {return ID;}/*** setter and getter .... */}

Ing file: dorm. HBM. xml

<? XML version = "1.0"?> <! Doctype hibernate-mapping public "-// hibernate/hibernate DTD ing DTD 3.0 // en" "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd"> 
Entity: Student (student. Java)
Package Org. wiksys. chap02.bean;/*** student class ** @ author wiksys **/public class student implements Java. io. serializable {private long ID; private dorm; private string name;/*** setter and getter */}
Ing file: Student. HBM. xml
<? XML version = "1.0"?> <! Doctype hibernate-mapping public "-// hibernate/hibernate DTD ing DTD 3.0 // en" "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd"> 
 
Common attributes of sequence-to-one elements:


  

 
   
 
    
 
     
Attribute
 
     
Meaning and function
 
     
Required?
 
     
Default Value
 
    
 
    
 
     
Name
 
     
Name of the ing Class Property
 
     
Y
 
     
 
    
 
    
 
     
Class
 
     
Fully Qualified name of the associated class
 
     
N
 
     
 
    
 
    
 
     
Column
 
     
Associated Fields
 
     
N
 
     
 
    
 
    
 
     
Not-Null
 
     
Set whether the associated field is empty
 
     
N
 
     
False
 
    
 
    
 
     
Lazy
 
     
Load Policy
 
     
N
 
     
Proxy
 
    
 
    
 
     
Fetcj
 
     
Capture Policy
 
     
N
 
     
Select
 
    
 
   

  
Test: insert data:
Package Org. wiksys. chap02.test; import Org. hibernate. hibernateexception; import Org. hibernate. session; import Org. hibernate. sessionfactory; import Org. hibernate. transaction; import Org. hibernate. cfg. configuration; import Org. wiksys. chap02.bean. dorm; import Org. wiksys. chap02.bean. student; public class hibernatetest {/*** @ author wiksys * @ return test * @ Param ARGs */public static void main (string [] ARGs) {student = new student (); dorm = new dorm (); dorm. setname ("104"); student. setname ("Jerry"); student. setdorm (dorm); sessionfactory Sf = NULL; Session session = NULL; transaction Tx = NULL; try {Sf = new configuration (). configure (). buildsessionfactory (); Session = SF. opensession (); Tx = session. begintransaction (); Session. save (dorm); Session. save (student); Tx. commit ();} catch (hibernateexception e) {Tx. rollback (); E. printstacktrace ();} finally {session. close (); SF. close ();}}}
 
2. ont-to-memory
One-to-one association: one-way multi-to-one Association
Case: dormitory and students
Multiple students in one dormitory
Is multiple-to-one. Add a record for the same exercise
The SQL script is the same as the preceding one.
Dormitory class: dorm. Java
Package Org. wiksys. chap02.bean2; import Java. util. hashset; import Java. util. set;/*** dormitory table * @ author wiksys **/public class dorm implements Java. io. serializable {private long ID; private string name; // set to save private set <student> students = new hashset <student> ();/*** setter and getter */}
Ing file: dorm. HBM. xml
<? XML version = "1.0"?> <! Doctype hibernate-mapping public "-// hibernate/hibernate DTD ing DTD 3.0 // en" "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd"> 
Set attribute in One-to-pair


   

 
    
 
     
 
      
Attribute
 
      
Meaning and definition
 
      
Required
 
      
Default Value
 
     
 
     
 
      
Name
 
      
Name of the ing file Property
 
      
Y
 
      
 
     
 
     
 
      
Table
 
      
Target database table of association class
 
      
Y
 
      
 
     
 
     
 
      
Lazy
 
      
Specify whether the associated object uses a delayed loading policy
 
      
N
 
      
Proxy
 
     
 
     
 
      
Fetch
 
      
Capture Policy
 
      
N
 
      
Select
 
     
 
    

   
 
Student: Student. Java
Package Org. wiksys. chap02.bean2;/*** student table * @ author wiksys **/public class student implements Java. io. serializable {private long ID; private long dormid; private string name;/*** setter and getter */}
Ing file: Student. HBM. xml
<?xml version="1.0"?><!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN""http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
By the way, you must register the ing file in hibernate. cfg. xml:
<! -- Chapter 2 many-to-one --> <! -- <Mapping Resource = "org/wiksys/chap02/bean/dorm. HBM. XML "/> <Mapping Resource =" org/wiksys/chap02/bean/student. HBM. XML "/> --> <! -- Chapter two: one-to-many --> <Mapping Resource = "org/wiksys/chap02/bean2/dorm. HBM. XML "/> <Mapping Resource =" org/wiksys/chap02/bean2/student. HBM. XML "/>
 
Test one to multiple:
Package Org. wiksys. chap02.test; import Org. hibernate. hibernateexception; import Org. hibernate. session; import Org. hibernate. sessionfactory; import Org. hibernate. transaction; import Org. hibernate. cfg. configuration; import Org. wiksys. chap02.bean2. dorm; import Org. wiksys. chap02.bean2. student; public class hibernatetest2 {/*** @ author wiksys * @ return test * @ Param ARGs */public static void main (string [] ARGs) {student = new student (); student. setname ("Jerry"); dorm = new dorm (); dorm. setname ("104"); dorm. getstudents (). add (student); sessionfactory Sf = NULL; Session session = NULL; transaction Tx = NULL; try {Sf = new configuration (). configure (). buildsessionfactory (); Session = SF. opensession (); Tx = session. begintransaction (); Session. save (dorm); Session. save (student); Tx. commit ();} catch (hibernateexception e) {Tx. rollback (); E. printstacktrace ();} finally {session. close (); SF. close ();}}}
 
Source code: http://download.csdn.net/detail/wiksys/4545505
Related jar files: http://download.csdn.net/detail/wiksys/4545524