Db4o Learning (7)-inheritance Association

1. Save inheritance

 // C # & JAVA Employee e1 = New Employee (" Michael "," 1234 "," Michael ", 101 ," 10/5/1975 "); Manager M1 = New Manager (" Sue "," 9876 "," Sue ", 102 ," 3/8/1982 "); Casualemployee C1 = New Casualemployee ("Tim "," 5544 "," Tim ", 103 ," 7/6/1986 "); Customer cu1 = New Customer (" Gary "," 408 123 4567 "," Gary@example.net ", New Address (" 1 First Street "," San Jose "," USA "));

// JavaDB. Set (E1); DB. Set (M1); DB. Set (C1); DB. Set (cu1 );
 

Save them separately.

 

2. query Manager

 
// JavaManager managerexample =NewManager (Null,Null,Null, 0,Null); Objectset Results = dB. Get (managerexample );
 

 

Query parent class employee:

 
// JavaEmployee employeeexample =NewEmployee (Null,Null,Null, 0,Null); Objectset Results = dB. Get (employeeexample );
 

Output itself and the inherited class:

Tim (casualemployee) Sue (manager) MICHAEL (employee)
 

 

Query abstract classes or interfaces to obtain all objects:

 
// JavaObjectset Results = dB. Get (abstractperson.Class);
 

 
Or
 

 
// JavaObjectset Results = dB. Get (person.Class);
 

 

Output:

 
Gary (customer) Tim (casualemployee) Sue (manager) MICHAEL (employee)
 

 

3. array attributes

 Public   Class Casualemployee Extends Employee { Double [] _ Timerecord;Final   Int Maxtimerecords = 10; Int Numberoftimerecords; Public Casualemployee (string name, string phonenumber, string email, Int Employeenumber, string DOB ){ Super (Name, phonenumber, email, employeenumber, DOB); _ timerecord = New   Double [Maxtimerecords]; numberoftimerecords = 0 ;} Public   Double [] Gettimerecord (){ Return _ Timerecord ;} Public   Void Settimerecord ( Double [] Timerecord) {_ timerecord = timerecord ;} Public   Void Addtimerecord ( Double Newrecord ){ If (Numberoftimerecords <maxtimerecords) {_ timerecord [numberoftimerecords] = newrecord; numberoftimerecords ++ ;}}Public String tostring (){ Return   Super . Getname () +" (Casualemployee) ";}}

 

Save:

// C # & JAVACasualemployee C1 =NewCasualemployee ("Tim","5544","Tim", 101 ,"7/6/1986"); Casualemployee C2 =NewCasualemployee ("Eva","4433","Eva", 102 ,"11/3/1984"); Round (2.5); c1.addtimerecord (4.0); c1.addtimerecord (1.5); Round (2.0); c2.addtimerecord (3.5); c2.addtimerecord (4.0); c2.addtimerecord (5.0 );
 

 
// JavaDB. Set (C1); DB. Set (C2 );
 

Query:

Casualemployee casempexample =NewCasualemployee (Null,Null,Null, 0,Null); Casempexample. settimerecord (New Double[] {4.0}); objectset Results = dB. Get (casempexample );
 

Or further:

 
// JavaCasualemployee casempexample =NewCasualemployee (Null,Null,Null, 0,Null); Casempexample. settimerecord (New Double[] {2.5, 4.0}); objectset Results = dB. Get (casempexample );
 

 

NQ query:

 
List <casualemployee> casemps = dB. Query (NewPredicate <casualemployee> (){Public BooleanMatch (casualemployee casemp ){ReturnArrays. binarysearch (casemp. gettimerecord (), 2.5)> = 0 & arrays. binarysearch (casemp. gettimerecord (), 4.0)> = 0 ;}
 

 

Soda query:

 
// JavaQuery query = dB. Query (); query. constrain (casualemployee.Class); Query valuequery = query. Descend ("_ Timerecord"); Valuequery. constrain (2.5); valuequery. constrain (4.0); objectset Results = query.exe cute ();
 

 

4. Update and delete array attributes

Update:

// JavaCasualemployee casempexample =NewCasualemployee ("Tim",Null,Null, 0,Null); Objectset Results = dB. get (casempexample); casualemployee Ce = (casualemployee) results. next (); ce. addtimerecord (6.0); ce. gettimerecord () [0] = 7.0; dB. set (CE );
 

For a numeric array, it is not necessary to set cascadeonupdate for this to work.

5. Set Operations:

 Public   Class Project {string _ name; string _ costcode; List <employee> _ employees; Public Project (string name, string costcode) {_ name = Name; _ costcode = costcode; _ employees = New Arraylist <employee> ();} Public Project (string name, string costcode, list <employee> employees) {_ name = Name; _ costcode = costcode; _ employees = employees ;} Public   Void Assignemployee (employee newemployee) {_ employees. Add (newemployee ); If (! Newemployee. Projects (). Contains ( This ) Newemployee. assigntoproject ( This );}Public List <employee> employees (){ Return _ Employees ;} Public String tostring (){ Return _ Name +" (Project) ";}}

 

Storage:

 // C # & JAVA Employee e1 = New Employee (" Michael "," 1234 "," Michael ", 101 ," 10/5/1975 "); Employee e2 = New Employee (" Anne "," 5432 "," Anne ", 102 ," 8/5/1980 "); Casualemployee C1 = New Casualemployee (" Tim "," 5544 "," Tim ", 103 ," 7/6/1986 "); Casualemployee C2 = New Casualemployee (" Eva ","4433 "," Eva ", 104 ," 11/3/1984 "); Project p1 = New Project (" Finance System "," P01 "); Project P2 = New Project (" Web Site "," PO2 ");

 
// JavaP1.assignemployee (E1); p1.assignemployee (C1); p2.assignemployee (C2); DB. Set (P1); DB. Set (P2 );
 

By storing a project, the employee is automatically stored.

 

Query:

When you retrieve a structured object, then by default you also get associated objects. This
Includes objects that are contained in a collection, so when you retrieve a project, you shoshould
Also retrieve the employees, if the activation depth allows it.

If the activation depth permits, You can query the employee ID at the same time.

 

 
Project projectexample =NewProject (Null,"P01"); Objectsset Results = dB. Get (projectexample );While(Results. hasnext () {project proj = (Project) results. Next (); system. Out. println (proj );For(Employee EMPL: proj. Employees) {system. Out. println (EMPL );}}
 

 
Query by set:
 

// JavaEmployee EMP =NewEmployee ("Anne",Null,Null, 0,Null); List <employee> emplist =NewArraylist <employee> (); emplist. Add (EMP); Project projectexample =NewProject (Null,Null, Emplist); objectset Results = dB. Get (projectexample );
 

If you only need to access the employee in the same project without other project attributes, you can:

Employee EMP =NewEmployee ("Anne",Null,Null, 0,Null); List <employee> emplist =NewArraylist <employee> (); emplist. Add (EMP); objectset Results = dB. Get (emplist );
 

 
NQ version:
 

List <project> projects = dB. Query (NewPredicate <project> (){Public BooleanMatch (Project proj ){For(Employee EMPL: proj. Employees ()){If(EMPL. getname (). Equals ("Michael")){Return True;}}Return False;}});
 

 

Soda version:

// JavaQuery query = dB. Query (); query. constrain (project.Class); Query empquery = query. Descend ("_ Employees"); Empquery. constrain (employee.Class); Query namequery = empquery. Descend ("_ Name"); Namequery. constrain ("Michael"); Objectset Results = query.exe cute ();
 

6. Update and delete collections

// JavaProject projectexample =NewProject (Null,"P02"); Objectset Results = dB. Get (projectexample );While(Results. hasnext () {project proj = (Project) results. Next ();For(Employee EMPL: proj. Employees () {EMPL. setemail (EMPL. getemail () +". Web");} DB. Set (proj );}
 

 
// JavaDB. Delete (proj. Employees (); DB. Delete (proj );
 

If only the project is deleted, and cascade deletion is not set, the employee will remain in the database.