How to get an array from an array in Meteor.js

Question

everyone. I would like the students who enroll a subject are shown in a table when this subject is selected in a dropdown list. The ID of these students is stored in an array. The problem is that this ID array retrieved from the document looks kind of strange. seem like there is an array in an array. Like this shown in the console: shown in console

 {enrollment: Array(2)}
     enrollment: Array(2)
     0: "b1602231"   
     1: "B1560124"   
     length: 2 
     __proto__: Array(0)
     __proto__: Object

And it throwed an error: Exception in template helper: Error: $in needs an array

So how could I solve this? I would really appreciate it if someone can give me some idea.

Below is the event handler and helper.

Template.subject.events({
  ‘change #dropdown’: function(event, template) {
    var selectedValue = $(event.target).val();
    var array = subject.findOne( { subjectCode:selectedValue }, { fields:{ _id:0, enrollment:1 } } );
    Session.set(‘studentEnrolled’,array);
  }
});

Template.student.helpers({
  student: function() {
    var listOfStudent = Session.get( ‘studentEnrolled’ );
    return student.find( { studentID: { $in:listOfStudent } } );
  }
});

//HTML

<template name="student">
        {{#each student}}
        <tr>
          <td>{{name}}</td>
        </tr>
        {{/each}}
</template>

Are you sure there's an array within an array? From what I can see it looks like there is just a single array in the console output. — Leafyshark
– Leafyshark, Commented Mar 29, 2020 at 13:03
@Leafyshark I am not sure about that. Because that __proto__ attribute confuses me. — BlueNut
– BlueNut, Commented Mar 29, 2020 at 13:48
please can you edit your post with a screenshot of the console.log instead of copy/paste? — Leafyshark
– Leafyshark, Commented Mar 29, 2020 at 14:00

coagmano · Accepted Answer · 2020-03-30 00:08:54Z

1

Copying my answer from the forums:

First of all, you are taking the whole subject document (and after the first answer, wrapping that array into another array) here:

Session.set('studentEnrolled',[array]);

Which means when you search here:

return student.find({studentID:{$in:listOfStudent}});

You are passing an array with a document in it, instead of the enrollments array.

What you want to do is store the enrollments in the session:

Session.set('studentEnrolled', array.enrollments);

I'd also recommend renaming the variable array since it's not an array, and that probably contributed to your confusion

answered Mar 30, 2020 at 0:08

coagmano

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xdeepakv · Accepted Answer · 2020-03-29 14:22:20Z

1

Find get one records from data. u can convert in array using [data]

var array = subject.findOne({subjectCode:selectedValue}, {fields:{_id:0, enrollment:1}});
Session.set(‘studentEnrolled’,[array]);
}

// For async update More: https://blog.meteor.com/using-promises-and-async-await-in-meteor-8f6f4a04f998

Template.hello.onCreated(function helloOnCreated() {
  this.list = new ReactiveVar([]);
  Meteor.call('getHobbits', (error, result) => {
    this.list.set(result);
  });
});

Template.hello.helpers({
  hobbits() {
    return Template.instance().list.get();
  },
});

edited Mar 29, 2020 at 14:22

answered Mar 29, 2020 at 13:04

xdeepakv

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4 Comments

BlueNut Over a year ago

Thanks.That error is fixed. But students are not showing in the table. Any idea?

BlueNut Over a year ago

Thanks, I will check it out.

xdeepakv Over a year ago

Ig helps. please upvoate :-D

BlueNut Over a year ago

I wish I could but I have to earn enough reputation to upvote :( Sorry about that.

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