iOS Development Made Simple!

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.

Aggregation On A UML Diagram Is Shown With A Simple Arrow In front
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

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)
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