Unidirectional N: 1 no intermediate table ing

Relationship between employees and departments: if an employee can only belong to one department, the relationship between the employee and the Department is N: 1. If the employee can only find the department to which the employee belongs, instead of finding the corresponding employee from the Department, this becomes a one-way N: 1 Association.

Hibernate tool (simple test)

 Public   Class  Hibernateutil {  Private   Static   Final Sessionfactory = Buildsessionfactory ();  Private   Static  Sessionfactory buildsessionfactory (){  Try  { //  Create the sessionfactory from hibernate. cfg. xml          Return   New  Configuration (). Configure (). buildsessionfactory ();}  Catch  (Exception ex ){  //  Make sure you log the exception, as it might be swallowed System. Out. println ("Initial sessionfactory creation failed." + Ex );  Throw   New Exceptionininitializererror (Ex );}}  Public   Static  Sessionfactory getsessionfactory (){  Return  Sessionfactory ;}  Public   Static  Session getsession () {sessionfactory SF = Getsessionfactory ();  Return  SF. opensession ();}} 

Employee

Public class employee {private long ID; private string name; private department Department; public long GETID () {return ID;} public void setid (long ID) {This. id = ID;} Public String getname () {return name;} public void setname (string name) {This. name = Name;} public department getdepartment () {return Department;} public void setdepartment (Department) {This. department = Department ;}}
 

Employee configuration file

 <?  XML version = "1.0" encoding = "UTF-8"  ?>  <!  Doctype hibernate-mapping public "-// hibernate/hibernate mapping DTD 3.0 //" http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd"  > <  Hibernate-Mapping  >      <  Class  Name  = "Com. longtech. hibernate. domain. Employee"  Table  = "Employee"  >           <  ID  Name  = "ID"  Column  = "ID" Type  = "Java. Lang. Long"   >              <  Meta  Attribute  = "Field-description"  > Unique Identifier </  Meta  >              <  Generator  Class  = "Native"  />         </  ID  >          <  Property  Name  = "Name"  Type  = "Java. Lang. String"  Column  = "Name"  Length  = "20"  >              <  Meta  Attribute = "Field-description"  > Employee name </  Meta  >          </  Property  >          <  Allow-to-one  Name  = "Department"  Column  = "Dept_id"  Cascade= "All" > </  Allow-to-one  >      </  Class  >  </  Hibernate-Mapping  > 

Department

 Public   Class  Department {  Private  Long ID;  Private  String name; Public  Long GETID (){  Return  ID ;}  Public   Void  Setid (long ID ){  This . ID = ID ;}  Public  String getname (){  Return  Name ;}  Public   Void Setname (string name ){  This . Name = Name ;}} 

 

Department configuration file

 <?  XML version = "1.0" encoding = "UTF-8"  ?>  <!  Doctype hibernate-mapping public "-// hibernate/hibernate mapping DTD 3.0 //" http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd"  >  <  Hibernate-Mapping  >     <  Class  Name  = "Com. longtech. hibernate. domain. Department"  Table  = "Department"  >           <  ID  Name  = "ID"  Column  = "ID"  Type  = "Java. Lang. Long"   >             <  Meta  Attribute  = "Field-description"  > Unique Identifier </  Meta  >              <  Generator  Class  = "Native"  />          </  ID  >          < Property  Name  = "Name"  Type  = "Java. Lang. String"  Column  = "Name"  Length  = "20"  >              <  Meta  Attribute  = "Field-description"  > Department name </ Meta  >          </  Property  >      </  Class  >  </  Hibernate-Mapping  > 

Persistence class

Department dept =NewDepartment (); Dept. setname ("Department"); Employee emp1=NewEmployee (); emp1.setname ("Emp1"); Emp1.setdepartment (Dept); Session. Save (emp1 );
 

In the persistence class, when session. Save (emp1) is executed, if cascade = "all" is not specified, the org. hibernate. transientobjectexception exception is thrown during execution.

After the preceding operations, you can find thatProgramThe database generates two records.

The console will enter two records:

 
Hibernate: insert into Department (name) values (?) Hibernate: insert into employee (name, dept_id) values (?, ?)
 

If cassade = "all" is used, the database inserts the department record first, and then inserts the employee record. Otherwise, it reports an exception. In fact, this logic is the same as that used to operate databases through JDBC. If the Department is not inserted first, the foreign key cannot be referenced.