Hibernate Framework Learning Note 4: Primary key generation policy, object state

Create an entity class:

 Packagedomain; Public classCustomer {PrivateLong cust_id; PrivateString Cust_name; PrivateString Cust_source; PrivateString Cust_industry; PrivateString Cust_level; PrivateString Cust_linkman; PrivateString Cust_phone; PrivateString Cust_mobile;  PublicLong getcust_id () {returncust_id; }     Public voidsetcust_id (Long cust_id) { This. cust_id =cust_id; }     PublicString Getcust_name () {returnCust_name; }     Public voidsetcust_name (String cust_name) { This. Cust_name =Cust_name; }     PublicString Getcust_source () {returnCust_source; }     Public voidSetcust_source (String cust_source) { This. Cust_source =Cust_source; }     PublicString getcust_industry () {returnCust_industry; }     Public voidsetcust_industry (String cust_industry) { This. Cust_industry =Cust_industry; }     PublicString Getcust_level () {returnCust_level; }     Public voidsetcust_level (String cust_level) { This. Cust_level =Cust_level; }     PublicString Getcust_linkman () {returnCust_linkman; }     Public voidSetcust_linkman (String cust_linkman) { This. Cust_linkman =Cust_linkman; }     PublicString Getcust_phone () {returnCust_phone; }     Public voidSetcust_phone (String cust_phone) { This. Cust_phone =Cust_phone; }     PublicString Getcust_mobile () {returnCust_mobile; }     Public voidsetcust_mobile (String cust_mobile) { This. Cust_mobile =Cust_mobile; } @Override PublicString toString () {return"Customer [cust_id=" + cust_id + ", cust_name=" + Cust_name + "]"; }}

View Code

ORM Meta-Data configuration file:

<?XML version= "1.0" encoding= "UTF-8"?><!DOCTYPE hibernate-mapping Public "-//hibernate/hibernate mapping DTD 3.0//en" "Http://www.hibernate.org/dtd/hib Ernate-mapping-3.0.dtd ">   <!--Configure the relationship between a table and an entity object -<hibernate-mapping>    <classname= "domain. Customer "Table= "Cst_customer" >        <IDname= "cust_id"  >            <!--Generator: Primary key generation Policy -            <Generatorclass= "Native"></Generator>        </ID>        < Propertyname= "Cust_name"column= "Cust_name" ></ Property>        < Propertyname= "Cust_source"column= "Cust_source" ></ Property>        < Propertyname= "Cust_industry"column= "Cust_industry" ></ Property>        < Propertyname= "Cust_level"column= "Cust_level" ></ Property>        < Propertyname= "Cust_linkman"column= "Cust_linkman" ></ Property>        < Propertyname= "Cust_phone"column= "Cust_phone" ></ Property>        < Propertyname= "Cust_mobile"column= "Cust_mobile" ></ Property>    </class></hibernate-mapping>

The primary key generation strategy here is native

With:

Primary key generation policy. Is the generation rule of the primary key when each record is entered. (7)

Identity: Primary key self-increment. The primary key value is maintained by the database. You do not need to specify a primary key when entering.

The primary key generation strategy in Sequence:oracle, where MySQL is used, temporarily does not introduce

Increment (not used, inefficient, and thread-safe issues): primary key self-increment. It is maintained by hibernate. The maximum ID value in the table is queried before each insert. +1 as the new primary key value.

Hilo (not used, understood): High-low algorithm, primary key self-increment. It is maintained by hibernate and is not used during development.

Native:hilo+sequence+identity automatic three-choice policy (detects the current database, using the appropriate policy)

UUID: Produces a random string that theoretically never repeats as a primary key. The primary key type must be of type string.

Assigned: Natural primary key generation strategy. Hibernate does not manage the primary key values, which are entered by the developer themselves.

Hibernate objects are divided into three states:

transient status : No ID, no session Association

Persistent state : with ID, associated with session

Free State ( managed state ): ID, not associated with session

 PackageState ;Importorg.hibernate.Session;Importorg.hibernate.SessionFactory;Importorg.hibernate.Transaction;Importorg.hibernate.cfg.Configuration;Importorg.junit.Test;ImportCn.itheima.domain.Customer;Importcn.itheima.utils.HibernateUtils;//three state of the test object Public classDemo {@Test//View three statuses     Public voidfun1 () {//1 Getting sessionSession session =hibernateutils.opensession (); //2 Control TransactionsTransaction tx =session.begintransaction (); //3 Performing ActionsCustomer C =NewCustomer ();//no ID, no associated with session--instantaneous stateC.setcust_name ("Lenovo");//instantaneous StateSession.save (c);//persistent state, with ID, associated//4 Commit the transaction. Close ResourceTx.commit (); Session.close ();//Free | Managed state, with ID, no association} @Test//three types of state features//Save Method: Actually can not understand to save. A method of translating transient state into a persistent state//PRIMARY Key increment: Executes the Save method in order to convert the object to a persisted state. ID values must be generated. Therefore, an INSERT statement generation is required. //If the primary key generation policy isIncrement: Executes the Save method in order to generate the ID. The SQL statement (select MAX (ID) from table) that executes the query ID maximum value .     Public voidfun2 () {//1 Getting sessionSession session =hibernateutils.opensession (); //2 Control TransactionsTransaction tx =session.begintransaction (); //3 Performing ActionsCustomer C =NewCustomer ();//no ID, no associated with session--instantaneous stateC.setcust_name ("Lenovo");//instantaneous StateSession.save (c);//persistent state, with ID, associated//4 Commit the transaction. Close ResourceTx.commit (); Session.close ();//Free | Managed state, with ID, no association} @Test//three types of state features//Persistence State feature: Any changes to the persisted state object are automatically synchronized to the database.     Public voidFun3 () {//1 Getting sessionSession session =hibernateutils.opensession (); //2 Control TransactionsTransaction tx =session.begintransaction (); //3 Performing ActionsCustomer C= Session.get (Customer.class, 1l);//persisted state ObjectC.setcust_name ("Microsoft Corporation"); //4 Commit the transaction. Close ResourceTx.commit (); Session.close ();//Free | Managed state, with ID, no association                    }}

Next, analyze Hibernate's additions and deletions from the state perspective:

Hibernate Framework Learning Note 4: Primary key generation policy, object state