JPA video learning (3) bidirectional one-to-Multiple Association Configuration

1. Persistence. xml 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 = "Jpaonetomanypu"   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  > 

 

2. Configuration entity:

Order entity:
ImportJava. util. hashset;
ImportJava. util. Set;

ImportJavax. Persistence. cascadetype;
ImportJavax. Persistence. column;
ImportJavax. Persistence. entity;
ImportJavax. Persistence. fetchtype;
ImportJavax. Persistence. ID;
ImportJavax. Persistence. oneto133;
ImportJavax. Persistence. Table;

@ Entity
@ Table (name ="Orders")
Public ClassOrder {
/**
* In a bidirectional one-to-multiple relationship, multiple parties are the maintenance end of the relationship.
* The maintenance end of The Link updates the foreign key field (record;
* The maintenance end of the link does not have the power to update the foreign key field (record.
*/

PrivateString orderid;
PrivateFloat amount = 0f;
PrivateSet <orderitem> items =NewHashset <orderitem> ();

@ ID// Assign values manually
@ Column (length = 12)
PublicString getorderid (){
ReturnOrderid;
}
Public VoidSetorderid (string orderid ){
This. Orderid = orderid;
}

@ Column (nullable = False )
Public Float getamount (){
Return Amount;
}
Public Void Setamount (float amount ){
This . Amount = amount;
}
Public Void Setitems (set <orderitem> items ){
This . Items = items;
}
/**
* Cascadetype. Refresh, cascadetype. persist, cascadetype. merge, cascadetype. Remove
* There are application conditions, that is, it is valid to call em. Refresh, Em. persist, Em. merge, Em. Remove.
* If query is used for update, deletion and addition are invalid.
*
* Refresh is the latest entity obtained from the database:
* Because the entity obtained in Em. Find may be different from the actual processing time,
* During these times, the entity may be updated to the database by other methods, but the EM cache has not changed,
* Therefore, you must use refresh to obtain the latest object.
*
* // Delayed loading must ensure that EM is on
// If tomany is used, loading is delayed by default.
// If it is toone, it is loaded immediately by default.
// Use mappedby to declare the maintenance end of the link. This indicates which attribute of the orderitem class maintains the link.
// In which class mappedby is displayed, the object indicates that the link is maintained.
*/
@ Onetosh (cascade = {cascadetype. Refresh, cascadetype. persist
, Cascadetype. merge, cascadetype. Remove}
, Fetch = fetchtype. Lazy
, Mappedby ="Order ")
Public Set <orderitem> getitems (){
Return Items;
}

// Establish link Maintenance
Public VoidAddorderitem (orderitem ){
Orderitem. setorder (This);// Set orderitem on the Link maintenance end to maintain the link
This. Items. Add (orderitem );
}
}

Orderitem entity:

 Import Javax. Persistence. cascadetype; Import Javax. Persistence. column; Import Javax. Persistence. entity; Import Javax. Persistence. generatedvalue; Import Javax. Persistence. ID; Import Javax. Persistence. joincolumn; Import Javax. Persistence. manytoone; @ entity Public   Class Orderitem { /*** In a bidirectional one-to-multiple relationship, multiple parties are the maintenance end of the link. * The maintenance end of the link is responsible for updating the foreign key field (record); * The maintenance end of the link is not authorized to update the foreign key field (record. */  Private Integer ID; Private String productname; Private Float pricefloat = 0f;Private Order order; Public Orderitem (){} Public Orderitem (string, Float F ){ This . Pricefloat = F; This . Productname = string ;} Public   Void Setid (integer ID ){ This . ID = ID;} @ ID @ generatedvalue Public Integer GETID (){ Return ID ;} Public  Void Setproductname (string productname ){ This . Productname = productname;} @ column (length = 40, nullable = False ) Public String getproductname (){ Return Productname ;} Public   Void Setpricefloat (float pricefloat ){ This . Pricefloat = pricefloat;} @ column (nullable = False ) Public Float getpricefloat (){ Return Pricefloat ;}Public   Void Setorder (order ){ This . Order = order ;} // Update the total price @ Manytoone (cascade = {cascadetype. merge, cascadetype. Refresh}, optional = False ) // Set the foreign key name @ Joincolumn (name =" Orderid ") Public Order getorder (){ Return Order ;}}

3. JUnit test:

 Package JUnit. test; Import Javax. Persistence. entitymanager; Import Javax. Persistence. entitymanagerfactory; Import Javax. Persistence. persistence; Import Org. JUnit. beforeclass; Import Org. JUnit. test; Import Com. Persia. Bean. Order; Import Com. Persia. Bean. orderitem; Public   Class Manytoonetest {@ beforeclass Public   Static   Void Setupbeforeclass ()Throws Exception {} // @ Test  Public   Void Save () {entitymanagerfactory FAC = persistence. createentitymanagerfactory (" Jpaonetomanypu "); // 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 (); Order order = New Order (); Order. setamount (34f); Order. setorderid (" 999 "); Order. addorderitem ( New Orderitem (" Football ", 90f); Order. addorderitem (New Orderitem (" Basketball ", 100f); em. persist (order); em. gettransaction (). Commit (); em. Close (); FAC. Close ();} // @ Test  Public   Void Getorder (){ // You do not need to enable the transaction for reading. Entitymanagerfactory FAC = persistence. createentitymanagerfactory (" Jpaonetomanypu "); Entitymanager em = FAC. createentitymanager (); order o = em. Find (Order. Class ," 999 "); // If no data exists, null is returned. System. Out. println (O. getorderid () +": "+ O. getamount (); em. Close (); FAC. Close ();} // @ Test  Public   Void Getorderitemsbyorder (){ // You do not need to enable the transaction for reading. Entitymanagerfactory FAC = persistence. createentitymanagerfactory (" Jpaonetomanypu "); Entitymanager em = FAC. createentitymanager (); order o = em. Find (Order. Class ," 999 "); // If no data exists, null is returned. System. Out. println (O. getorderid () +" : "+ O. getamount ()); For (Orderitem OTM: O. getitems () system. Out. println (OTM. getproductname () +" : "+ OTM. getpricefloat (); em. Close (); FAC. Close ();} // @ Test  Public   Void Getorderitems (){ // You do not need to enable the transaction for reading. Entitymanagerfactory FAC = persistence. createentitymanagerfactory (" Jpaonetomanypu "); Entitymanager em = FAC. createentitymanager (); orderitem OTM = em. Find (orderitem. Class , 1 ); // If no data exists, null is returned. System. Out. println (OTM. getproductname () +" : "+ OTM. getpricefloat (); system. Out. println ("Order ID: "+ OTM. getorder (). getorderid (); em. Close (); FAC. Close ();} // @ Test  Public   Void Updateorder () {entitymanagerfactory FAC = persistence. createentitymanagerfactory (" Jpaonetomanypu "); Entitymanager em = FAC. createentitymanager (); em. gettransaction (). Begin (); // Start the transaction Order order = em. Find (Order. Class ," 999 "); Order. setamount (1000f); em. Merge (order ); // Synchronize updates to the entity bean in the Free State to the database. Em. gettransaction (). Commit (); // Submit the transaction Em. Close (); FAC. Close ();} /// @ Test // cascade update  Public   Void Updateordercascade () {entitymanagerfactory FAC = persistence. createentitymanagerfactory (" Jpaonetomanypu "); Entitymanager em = FAC. createentitymanager (); em. gettransaction (). Begin (); // Start the transaction Order order = em. Find (Order. Class ," 999 "); Order. setamount (2000f ); For (Orderitem OTM: Order. getitems () {OTM. setpricefloat (300f);} em. Merge (order ); // Synchronize updates to the entity bean in the Free State to the database. Em. gettransaction (). Commit ();// Submit the transaction Em. Close (); FAC. Close () ;}@ Test // Cascading Deletion  Public   Void Deleteorder () {entitymanagerfactory FAC = persistence. createentitymanagerfactory (" Jpaonetomanypu "); Entitymanager em = FAC. createentitymanager (); em. gettransaction (). Begin (); // Start the transaction Order order = em. Find (Order. Class ," 999 "); Em. Remove (order); em. gettransaction (). Commit (); // Submit the transaction Em. Close (); FAC. Close ();}}