JPA video learning (1) add, delete, modify, and query

1. Dependent jar package:

2. configuration file:

 <? XML version = "1.0" encoding = "UTF-8" ?>  <  Persistence   Xmlns = Http://java.sun.com/xml/ns/persistence"      Xmlns : Xsi = Http://www.w3.org/2001/XMLSchema-instance"      Xsi : Schemalocation =Http://java.sun.com/xml/ns/persistence http://java.sun.com/xml/ns/persistence/persistence_1_0.xsd"   Version = "1.0"  >      <  Persistence - Unit   Name = "Hellojpapu"   Transaction - Type = "Resource_local"  >  < Provider  > Org. hibernate. EJB. hibernatepersistence </  Provider  >    <  Properties  >        <  Property   Name = "Hibernate. dialect"   Value = "Org. hibernate. dialect. mysql5dialect"  /> <  Property   Name = "Hibernate. Connection. driver_class"   Value = "Com. MySQL. JDBC. Driver"  />  <  Property   Name = "Hibernate. Connection. url"   Value = "JDBC: mysql: // localhost: 3306/JPA? Useunicode = true & amp; characterencoding = UTF-8"  /> <  Property   Name = "Hibernate. Connection. username"   Value = "Root"  />  <  Property   Name = "Hibernate. max_fetch_depth"   Value = "3"  />              <  Property  Name = "Hibernate. hbm2ddl. Auto"   Value = "Update"  />      </  Properties  >  </  Persistence -Unit >    </  Persistence  > 

3. Define the object Bean:

 Import Java. util. date;Import Javax. Persistence. Basic; Import Javax. Persistence. column; Import Javax. Persistence. entity; Import Javax. Persistence. enumtype; Import Javax. Persistence. enumerated; Import Javax. Persistence. fetchtype; Import Javax. Persistence. generatedvalue; Import Javax. Persistence. generationtype; Import Javax. Persistence. ID; Import Javax. Persistence. lob;Import Javax. Persistence. Table; Import Javax. Persistence. Temporal; Import Javax. Persistence. temporaltype; Import Javax. Persistence. Transient; @ entity Public   Class Person { Private Integer ID; Private String name; Private Date birthday; // 1988-02-01  Private Gender gender = gender. Man;Private String Info; Private Byte [] file; Private String imagepathstring; Public Person (){} Public Person (string name ){ This . Name = Name ;}@ ID @ generatedvalue (Strategy = generationtype. Auto) Public Integer GETID (){ Return ID ;} Public   Void Setid (integer ID ){ This . ID = ID;} @ column (length = 10, nullable =False ) Public String getname (){ Return Name ;} Public   Void Setname (string name ){ This . Name = Name ;}@ temporal (temporaltype. Date) Public Date getbirthday (){ Return Birthday ;} Public   Void Setbirthday (date birthday ){ This . Birthday = birthday;} @ Enumerated (enumtype. String)// Save the index value to the database @ Column (length = 5, nullable = False ) // Set the length  Public Gender getgender (){ Return Gender ;} Public   Void Setgender (gender Gender ){ This . Gender = gender;} @ lob // Description of the big data field, which is a big text type on the string  Public String getinfo (){ Return Info ;} Public  Void Setinfo (string info ){ This . Info = Info;} @ lob // Big data field description, which is used to store binary data @ Basic (fetch = fetchtype. Lazy) // Delayed loading. The get method that accesses this attribute is loaded from the database to the memory,                              // At this time, you must ensure that EM is in the open state; otherwise, a delayed loading error occurs.  Public Byte [] GetFile (){ Return File ;} Public   Void Setfile (byte [] File ){ This . File = file ;} Public   Void Setimagepathstring (string imagepathstring ){ This . Imagepathstring = imagepathstring;} @ transient // This attribute is not a persistent Field  Public String getimagepathstring (){ Return Imagepathstring ;}}

 
Enumeration class:
 

 
PackageCom. Persia. JPA;PublicEnum gender {Man, woman}
 

4. Add a Test method:

 Package JUnit. test; Import Java. util. date; Import Javax. Persistence. entitymanager; Import Javax. Persistence. entitymanagerfactory; Import Javax. Persistence. persistence; Import Org. JUnit. beforeclass; Import Org. JUnit. test; Import Com. Persia. JPA. person; Public   Class Persontest {@ beforeclass Public   Static   Void Setupbeforeclass () Throws Exception {} // @ Test  Public  Void Save () {entitymanagerfactory FAC = persistence. createentitymanagerfactory (" Hellojpapu "); // At this time, the database table has been created. If there is no table, it is likely that the object annotation has an error. Entitymanager em = FAC. createentitymanager (); em. gettransaction (). Begin (); // Start the transaction Person = New Person (" Linda "); Person. setbirthday ( New Date (); em. persist (person); em. gettransaction (). Commit (); // Submit the transaction Em. Close (); FAC. Close ();} // @ Test  Public  Void Getperson (){ // You do not need to enable the transaction for reading. Entitymanagerfactory FAC = persistence. createentitymanagerfactory (" Hellojpapu "); Entitymanager em = FAC. createentitymanager (); person P = em. Find (person. Class , 1 ); // If no data exists, null is returned. System. Out. println (P. getname (); em. Close (); FAC. Close ();} // @ Test  Public   Void Getperson2 (){ // You do not need to enable the transaction for reading. Entitymanagerfactory FAC = persistence. createentitymanagerfactory (" Hellojpapu "); Entitymanager em = FAC. createentitymanager (); person P = em. getreference (person. Class , 2 ); // Delayed initialization. No record is obtained from the database immediately, but a proxy object is obtained. System. Out. println (P. getname ()); // When we access the properties of this proxy object, we get records from the database. At this time, we must ensure that EM is on; otherwise, delayed loading exceptions will occur.                                  // If the object does not exist during access, the exception entitynotfoundexception is thrown. Em. Close (); FAC. Close ();} // @ Test  Public   Void Updateperson () {entitymanagerfactory FAC = persistence. createentitymanagerfactory (" Hellojpapu "); Entitymanager em = FAC. createentitymanager (); em. gettransaction (). Begin ();// Start the transaction Person P = em. Find (person. Class , 1); p. setname (" Helloworld "); // This can be updated at this time, mainly including:  /*** 1. associated with the current transaction * 2. the status of the Entity Bean is managed. ** the state of the entity: * 1. create new * 2. managed management * 3. free (unmanageable) * 4. delete */ Em. gettransaction (). Commit (); // Submit the transaction Em. Close (); FAC. Close ();} // @ Test  Public   Void Updateperson2 () {entitymanagerfactory FAC = persistence. createentitymanagerfactory (" Hellojpapu "); Entitymanager em = FAC. createentitymanager (); em. gettransaction (). Begin (); // Start the transaction Person P = em. Find (person. Class , 1); em. Clear (); // Change all objects in the Entity Manager to a free State. In this case, use merge to update objects. P. setname (" Hello3 "); // This can be updated at this time, mainly including: Em. Merge (P ); // Synchronize updates to the entity bean in the Free State to the database. Em. gettransaction (). Commit (); // Submit the transaction Em. Close (); FAC. Close () ;}@ Test Public   Void Delete () {entitymanagerfactory FAC = persistence. createentitymanagerfactory ("Hellojpapu "); Entitymanager em = FAC. createentitymanager (); em. gettransaction (). Begin (); // Start the transaction Person P = em. Find (person. Class , 1); em. Remove (P ); // Delete the managed Entity Bean Em. gettransaction (). Commit (); // Submit the transaction Em. Close (); FAC. Close ();}}