Hibernate architecture introduction and environment construction (very detailed)

Catalog

1  Three layer architecture

2 hiberate summary

3 ORM thought

4 Hiberate Environment construction and various preparations ( Very detailed )

Basic preparation

Configure a correspondence

hibernate.cfg.xml Templates

Add operation steps

Test the whole code

Effect validation

5  Writing rules of entity classes

6  Primary key growth strategy

---

1  Three layer architecture

1、web layer ：struts2 frame

2、service layer ：spring frame

3、dao layer ：hiberate frame （ The database is crud operation ）

MVC thought ：model-view-controller

2 hiberate summary

stay javaEE In the three-tier architecture dao layer .

Hibernate The bottom is JDBC, Yes JDBC It was packaged , The advantage is that you don't need to write complex JDBC Code and SQL The statement implements .

Hibernate It's an open source 、 Lightweight （ It can be used directly without relying on other things 、 Import very few jar package ） Framework

Hibernate edition ：Hibernate3.x、4.x、5.x;4.x Is an over version

3 ORM thought

Hibernate Is an open source object relational mapping （orm-Object Relational Mapping） frame .

Hibernate This idea is used to crud operation .

Web Stage javaBean class , In the Framework phase, it is called Entity class .

Let entity classes and database tables have a one-to-one correspondence .

Attributes of a class -- The fields in the table correspond to

You don't need to directly manipulate database tables , The direct operation table corresponds to the entity class object .

Jdbc Code ：

Class.forName(“com.oracle.jdbc.driver”);

Connection = DriverManager.getConnection();

(url,username,password)

String sql=””;

ps = conn.prepareStatement(sql);

rs = ps.excuteQuery();

// Traversal result set 

// Release resources 

Entity class

Public class User{

Private int userid;

Private String username;

Private String password;

//set、get

}

Database table ：

Create table t_user(

Userid number not NULL AUTO_INCREATEMENT,

username varchar2(100),

password varchar2(100)

);

Use the configuration file to complete one-to-one correspondence

Hibernate Encapsulated objects Session：

User user = new User();

User.setUserName(“”);

Session.save(user); //session The method in 

4 Hiberate Environment construction and various preparations ( Very detailed )

Basic preparation

First step ： Import Hibernate Of jar package

require Folders and JPA In folder jar You have to import .

Because use Hibernate Log information is output from time to time ,Hibernate There is no log output in itself jar package , You need to import other logs jar The package supports these outputs .

2、 Create entity class

Hibernate Require an attribute in the entity class （ Such as id） Is the only one. .（ Such as the primary key in the table ）

private int userid;

3、 Create table （hibernate Automatically create ）

4、 Configure the mapping relationship between entity classes and database tables -- Configuration file implementation

establish xml The configuration file ： Configuration file name and location are not required , But it's usually called ：hbm.xml; The location is created under the package of the entity class .

First introduced xml constraint , Currently in hibernate Most of them are dtd constraint ; stay hibernate The constraint file for （hibernate-mapping-3.0.dtd） Copy the created from xml.

<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"

 "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd" >

Configure a correspondence

Create core profile

The location and name are fixed . Location --src Next ; name --hibernate.cfg.xml

hibernate.cfg.xml Templates

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-configuration PUBLIC
	"-//Hibernate/Hibernate Configuration DTD 3.0//EN"
	"http://www.hibernate.org/dtd/hibernate-configuration-3.0.dtd">

<hibernate-configuration>
	<session-factory>
	<!--1. Configuration database information  , There must be  -->
		<!--  Configure the dialect of the database , Such as ：MySQL The middle page is limit,oracle Medium is rownum; Give Way hibernate Identify statements or keywords in different databases  -->
		<property name="dialect">org.hibernate.dialect.OracleDialect</property>   
        <property name="hibernate.connection.driver_class">oracle.jdbc.driver.OracleDriver</property> 
        <property name="hibernate.connection.url">jdbc:oracle:thin:@127.0.0.1:1521:XE</property>  
        <property name="hibernate.connection.username">abc</property>  
        <property name="hibernate.connection.password">abc</property>  
		
	<!--2. To configure hibernate Information , There is nothing   -->
		<!--  Output bottom layer SQL -->
		<property name="hibernate.show_sql">true </property> 
		<!--  To the underlying SQL format , Formatting is not displayed on one line  -->
		<property name="hibernate.format_sql">true</property>
		
        <!--  Automatically generate or update database tables , Written words , The table will be created automatically  -->  
        <property name="hibernate.hbm2ddl.auto">update</property>  
    <!-- 3. Register map file  -->  
        <mapping resource="com/wl/entity/User.hbm.xml" />  <!--  With src For the relative path , If in src Next , Is directly User.hbm.xml -->
<!--  notes ：hibernate.hbm2ddl.auto The value of is create Indicates that a new table will be created each time ;
		 The value is create-drop It's closing SessionFactory Delete the fairy sword table ;
		 The value is update（ Common values ） If the first runtime database does not have a corresponding table , A new table will be created , But if there is a corresponding data table , No longer create the corresponding data table  -->
	</session-factory>
</hibernate-configuration>

Copy in dtd constraint ：

<?xml version='1.0' encoding='UTF-8'?>

<!DOCTYPE hibernate-configuration PUBLIC

          "-//Hibernate/Hibernate Configuration DTD 3.0//EN"

          "http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd"

hibernate In operation , Only the core configuration file... Will be loaded , Other configuration files will not load .

The following three parts are basically configured only once , After that, it is seldom modified .

The first part ： Configuration database information

The second part ： To configure hibernate Information

The third part ： Put the configuration file into the core configuration file

<property name="hibernate.dialect">org.hibernate.dialect.MySQLDialect</property>

<property name="hibernate.connection.driver_class">com.mysql.jdbc.Driver</property>

<property name="hibernate.connection.url">jdbc:mysql://localhost:3306/hibernate</property>

Add operation steps

First step ： load hibernate Core profile

The second step ： establish Sessionfactory Factory object

The third step ： Use Sessionfactory establish session object

Step four ： Open transaction , Manual creation is recommended

Step five ：curd operation

Step six ： Commit transaction

Step seven ： close resource

Change is only the fifth step , Other general purpose fixing .

Test the whole code

package com.wl.test;

import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.Transaction;
import org.hibernate.cfg.Configuration;
import org.junit.Test;

import com.wl.entity.User;
import com.wl.utils.HibernateUtils;

/*
 *  add to ：save()
 *  modify ：update()
 *  Delete ：delete()
 *  according to id Inquire about ：get()
 */
public class InsertDemo {

	
	/*
	 *  modify 
	 */
	@Test
	public void updateDemo(){
//		Configuration cfg = new Configuration();
//		cfg.configure();
		SessionFactory sessionFactory = HibernateUtils.getSessionFactory();
		Session session = sessionFactory.openSession();
		Transaction transaction = session.beginTransaction();
		User user = new User();
		user.setUserid(4);
		user.setUsername("rrr");
		user.setPassword("rrr");
		user.setAddress("AAAAA");
		session.update(user);
		transaction.commit();
		session.close();
		sessionFactory.close();
	}
	
	/*
	 *  Insert 
	 */
	@Test
	public void insertDemo1(){
		SessionFactory sessionFactory = HibernateUtils.getSessionFactory();
		Session session = sessionFactory.openSession();
		Transaction transaction = session.beginTransaction();
		User user = new User();
		user.setUsername("wl9");
		user.setPassword("000002");
		user.setAddress("XXXXX");
		session.save(user);
		transaction.commit();
		session.close();
		sessionFactory.close();
	}
	
	
	/*
	 *  Insert 
	 */
	@Test
	public void insertDemo(){
//		 First step ： load hibernate Core profile , Will be in src Look under hibernate.cfg.xml
		Configuration cfg = new Configuration();
		cfg.configure();
//		 The second step ： Read the contents of the core configuration file , To create Sessionfactory Factory object ; In the process , According to the mapping relationship , Create tables in the configuration database .
		SessionFactory sessionFactory = cfg.buildSessionFactory();
//		 The third step ： Use Sessionfactory establish session object , It's like connecting connection
		Session session = sessionFactory.openSession();
//		 Step four ： Open transaction , Manual creation is recommended 
		Transaction transaction = session.beginTransaction();
//		 Step five ：curd operation , Such as add operation 
		User user = new User();
		user.setUsername("123");
		user.setPassword("000002");
		user.setAddress("XX");
		// call session The method inside implements adding 
		session.save(user);
//		 Step six ： Commit transaction 
		transaction.commit();
//		 Step seven ： close resource 
		session.close();
		sessionFactory.close();
	}
	
}

Effect validation

1 Whether the table has been created ;

2 Whether records have been added .

Console ：

There are five sentences ：

Hibernate:

    update

        t_user

    set

        username=?,

        password=?,

        address=?

    where

        userid=?

Hibernate:

    select

        hibernate_sequence.nextval

    from

        dual

Hibernate:

    insert

    into

        t_user

        (username, password, address, userid)

    values

        (?, ?, ?, ?)

Hibernate:

    select

        hibernate_sequence.nextval

    from

        dual

Hibernate:

    insert

    into

        t_user

        (username, password, address, userid)

    values

        (?, ?, ?, ?)

In the database ：

select dbms_metadata.get_ddl('TABLE', ‘T_USER’) from dual;

  or desc see ：

5  Writing rules of entity classes

1. Property private , Provide get/set Method .
2. Have an attribute as the unique value , If you use id Distinguish between unique values .
3. For the data type of entity class, it is recommended to use the wrapper type of basic data type , Such as Integer,Character, Everything else is capitalized

If you use int Express score,int score=0; The score is 0 when , At this point, if you want to show that the students have not taken the exam, you can't realize , because int score=null; It's wrong. . It's time to use Integer score = null;

6  Primary key growth strategy

Primary key ： stay Hibernate Persistent classes in all have an identity attribute , Unique to identify the instance , This attribute maps to the primary key of the database table .

    key generator ：<generator class=" generation "/>

    The values of the generation method are ：

        increment： Indicates to obtain the maximum primary key value of the table in the database , and +1 As the new primary key .

        identity： Automatic growth , Mainly used in mysql,db2.

        Sequence：Hibernate Generate identifiers based on the underlying database sequence , The condition is that the database should support sequences . Applies to proxy primary keys .

        native：（ This method is generally selected during development ） Automatic growth ,Hibernate From the database identity,sequence( Sequence ),hilo( High low algorithm ) Select an appropriate method to generate a primary key , stay mysql Use identity, stay Oracle Select... In the middle sequence( Sequence ).

        uuid： Use UUID Algorithm generates string type primary key （ It is mainly used for distributed deployment ）.

Use uuid when , Change the primary key of the entity class to String type , Change the configuration file to uuid.

Run the encapsulated tool class , See the effect ：

Run the test data ：

in other words , When using uuid When a policy is generated as a primary key , You need to set the primary key to String type .