Arrays of objects nested within knockout arrays

Question

Arrays of objects nested within knockout arrays

As a newcomer to knockout, I am excited to dive into it head first. Here's my issue: I'm attempting to access a list (array) of objects within another list of objects (array).

For example: (to keep it simple)

Teacher -> Students

Teacher #1
- Student 1
- Student 2
- Student 3
Teacher #2
- Student 1
- Student 2
- Student 3
Teacher #3
- Student 1
- Student 2
- Student 3

While I've successfully displayed the list of all teachers, when it comes to displaying the list of students, the last node (Teacher #3) shows all the students from Teachers (#1, #2, and #3); while Teacher #1 and #2 are blank.

var ViewModel = {
       Teachers: ko.observableArray([])
}

function LoadTeachers(....) //Here Teacher list is loaded successfully.>

ko.applyBindings(ViewModel);


function teacher(T){
 this.TeacherID:ko.observable(T.TeacherID);
 this.TeacherName: ko.observable(T.TeacherName);

 this.StudentArray = ko.observableArray([]);

 function student(s){
    this.StudentID=ko.observable(s.StudentID);
    this.Name = ko.observable(s.s.Name);
 }

$.getJson('...');  // here is where Student array is loaded. 

}

then I would have in my view page:

foreach: Teacher  
foreach: Student

Drawing on my C# knowledge and applying it to knockout, I suspect the issue lies in declaring the Student Array inside the teacher object, since each student belongs to a specific teacher. In C#, this is how I would approach it.

Is there a way to make this coding work? I hope so!

Thank you in advance

javascript arrays knockout.js

Answer 1

Answer №1

For now, I am setting aside the Knockout mapping plugin (which has its merits but lacks in certain areas). This decision is aimed at presenting you with a straightforward solution. While you did encounter some peculiarities with knockout, the main issue was actually related to a closure mistake. The crucial part of the code lies within var newTeacher = .... It is vital to have this within the nested ajax closure. Below is the updated code along with a link to the functional fiddle:

$(document).ready(function(){
    var ViewModel = {
        Teachers: ko.observableArray([])
    };

    // Using fake data instead of actual ajax calls for demonstration purposes
    var fakeTeacherData = [{TeacherID: 1, TeacherName: 'Dan'}, {TeacherID: 2, TeacherName: 'Marian'}];
    var fakeStudentData = [{StudentID: 1, Name: 'Student 1'}, {StudentID: 2, Name: 'Student 2'}];

    $.get('/echo/json', function(teacherData){
        // Actual data usage will replace this section
        ko.utils.arrayForEach(fakeTeacherData, function(T){
            var newTeacher = new teacher(T);
            ViewModel.Teachers.push(newTeacher);

            $.get('/echo/json', function(studentData){
                // Actual data usage will replace this section   
                ko.utils.arrayForEach(fakeStudentData, function(S){
                    newTeacher.Students.push(new student(S));
                });
            });
        });
    });
    ko.applyBindings(ViewModel);
});

function teacher(T){
    this.TeacherID = ko.observable(T.TeacherID);
    this.TeacherName = ko.observable(T.TeacherName);
    this.Students = ko.observableArray([]);
}

function student(S){
    this.StudentID = ko.observable(S.StudentID);
    this.Name = ko.observable(S.Name);
}

http://jsfiddle.net/kXQxA/

Answer 2

For now, I am setting aside the Knockout mapping plugin (which has its merits but lacks in certain areas). This decision is aimed at presenting you with a straightforward solution. While you did encounter some peculiarities with knockout, the main issue was actually related to a closure mistake. The crucial part of the code lies within var newTeacher = .... It is vital to have this within the nested ajax closure. Below is the updated code along with a link to the functional fiddle:

$(document).ready(function(){
    var ViewModel = {
        Teachers: ko.observableArray([])
    };

    // Using fake data instead of actual ajax calls for demonstration purposes
    var fakeTeacherData = [{TeacherID: 1, TeacherName: 'Dan'}, {TeacherID: 2, TeacherName: 'Marian'}];
    var fakeStudentData = [{StudentID: 1, Name: 'Student 1'}, {StudentID: 2, Name: 'Student 2'}];

    $.get('/echo/json', function(teacherData){
        // Actual data usage will replace this section
        ko.utils.arrayForEach(fakeTeacherData, function(T){
            var newTeacher = new teacher(T);
            ViewModel.Teachers.push(newTeacher);

            $.get('/echo/json', function(studentData){
                // Actual data usage will replace this section   
                ko.utils.arrayForEach(fakeStudentData, function(S){
                    newTeacher.Students.push(new student(S));
                });
            });
        });
    });
    ko.applyBindings(ViewModel);
});

function teacher(T){
    this.TeacherID = ko.observable(T.TeacherID);
    this.TeacherName = ko.observable(T.TeacherName);
    this.Students = ko.observableArray([]);
}

function student(S){
    this.StudentID = ko.observable(S.StudentID);
    this.Name = ko.observable(S.Name);
}

http://jsfiddle.net/kXQxA/

Answer 3

Answer №2

To showcase students grouped by teacher, you can try a setup similar to this example.

Teacher = function (data) {
    var self = this;
    self.Id = ko.observable(data.Id || 0);
    self.Name = ko.observable(data.Name || '');
    // Refer to JSFiddle for mapping details
    self.Students = ko.mapping.fromJS(data.Students, StudentMapping);
    return self;
};

Student = function (data) {
    var self = this;
    self.Id = ko.observable(data.Id || 0);
    self.Name = ko.observable(data.Name || '');
    return self;
};

StaffViewModel = function (data) {
    var self = this;
    // Check JSFiddle for mapping reference
    ko.mapping.fromJS(data, StaffMapping, self);
    return self;
};

I am utilizing the original Knockout mapping plugin in this scenario, but feel free to explore the viewmodel plugin as well.

If your preference is to display students and teachers separately, it might be better not to make students observable properties of 'Teacher'. Instead, you can include code within the ViewModel constructor to generate a distinct list of students. The mapping plugin will still provide assistance here, especially with the 'key' function to avoid duplicates.

Answer 4

To showcase students grouped by teacher, you can try a setup similar to this example.

Teacher = function (data) {
    var self = this;
    self.Id = ko.observable(data.Id || 0);
    self.Name = ko.observable(data.Name || '');
    // Refer to JSFiddle for mapping details
    self.Students = ko.mapping.fromJS(data.Students, StudentMapping);
    return self;
};

Student = function (data) {
    var self = this;
    self.Id = ko.observable(data.Id || 0);
    self.Name = ko.observable(data.Name || '');
    return self;
};

StaffViewModel = function (data) {
    var self = this;
    // Check JSFiddle for mapping reference
    ko.mapping.fromJS(data, StaffMapping, self);
    return self;
};

I am utilizing the original Knockout mapping plugin in this scenario, but feel free to explore the viewmodel plugin as well.

If your preference is to display students and teachers separately, it might be better not to make students observable properties of 'Teacher'. Instead, you can include code within the ViewModel constructor to generate a distinct list of students. The mapping plugin will still provide assistance here, especially with the 'key' function to avoid duplicates.

Arrays of objects nested within knockout arrays

Answer №1

Answer №2

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