In this article we are going to continue our journey on getting a better grasp about Object Relations in Object Oriented Programming.
Let’s explore Aggregation.
We are speaking of an Aggregation when an Object is served as a container for a collection of other objects. For example, Imagine how a school department is served as a container for one or many teachers. At the same time, the very same school department can also be served as a container for one or many students.
The previous example helps us to get a better grasp on the following assumption:
Aggregation represents one to many or many to many relationships between objects.
However, in an Aggregation relationship objects can exist without their container object, for example a teacher and a student can exist without a specific school department. Keep in mind, objects of a container can be linked to multiple containers at the same time, for instance a teacher object can be an object of multiple departments.
And An Empty Diamond/ Squared Tail.
Object Department Knows About Object Teacher
Object Department Knows About Object Student
———-
Class Department Consists Of Teacher Object(s)
Class Department Consists Of Student Object(s)
Pseudo Code
//Student Class
class Student is
name: String
lastName: String
age: Integer
method constructor(String name, String lastName, Integer age) is
this.name = name
this.lastName = lastName
this.age = age
//Teacher Class
class Teacher is
name: String
lastName: String
age: Integer
method constructor(String name, String lastName, Integer age) is
this.name = name
this.lastName = lastName
this.age = age
//Software Department Class
class SoftwareDepartment is
private teachers: Array [Teacher]
private students: Array [Student]
method addTeacher(Teacher teacher) is
this.teachers.add(teacher)
method addStudent(Student student) is
this.students.add(student)
method getTeachers(): [Teacher] is
return this.teachers
method getStudents(): [Students] is
return this.students
//Design Department Class
class DesignDepartment is
private teachers: Array [Teacher]
private students: Array [Student]
method addTeacher(Teacher teacher) is
this.teachers.add(teacher)
method addStudent(Student student) is
this.students.add(student)
method getTeachers(): [Teacher] is
return this.teachers
method getStudents(): [Students] is
return this.students
Swift Code
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import Foundation class Student { let name: String let lastName: String let age: Int init(name: String, lastName: String, age: Int) { self.name = name self.lastName = lastName self.age = age } } class Teacher { let name: String let lastName: String let age: Int init(name: String, lastName: String, age: Int) { self.name = name self.lastName = lastName self.age = age } } class SoftwareDepartment { private var teachers: [Teacher] = [] private var students: [Student] = [] func addTeacher( _ teacher: Teacher) { self.teachers.append(teacher) } func addStudent( _ student: Student) { self.students.append(student) } func getStudent() -> [Student] { return self.students } func getTeacher() -> [Teacher] { return self.teachers } } class DesignDepartment { private var teachers: [Teacher] = [] private var students: [Student] = [] func addTeacher( _ teacher: Teacher) { self.teachers.append(teacher) } func addStudent( _ student: Student) { self.students.append(student) } func getStudent() -> [Student] { return self.students } func getTeacher() -> [Teacher] { return self.teachers } } //Object can exist without the container let student = Student(name: "Joseph", lastName: "Doe", age: 25) let teacher = Teacher(name: "Yasser", lastName: "Farahi", age: 34) //Objects can be linked to several containers at the same time let softwareDepartment = SoftwareDepartment() let designDepartment = DesignDepartment() //Adding Teacher to several departments softwareDepartment.addTeacher(teacher) designDepartment.addTeacher(teacher) //Adding Student to several departments softwareDepartment.addStudent(student) designDepartment.addStudent(student) print(softwareDepartment.getTeacher().first!.name, softwareDepartment.getTeacher().first!.lastName, softwareDepartment.getTeacher().first!.age) print(designDepartment.getTeacher().first!.name, designDepartment.getTeacher().first!.lastName, designDepartment.getTeacher().first!.age) print(softwareDepartment.getStudent().first!.name, softwareDepartment.getStudent().first!.lastName, softwareDepartment.getStudent().first!.age) print(designDepartment.getStudent().first!.name, designDepartment.getStudent().first!.lastName, designDepartment.getStudent().first!.age) |