Learning Node and MongoDb

app.js

/**
 * Created by hydee on 1/16/17.
 */
var Disease = require('./diseaseschema')
var disease;

var diseases = require('./getDiseases')
//saving to database.
diseases.diseaseDetails(function (diseaseData) {

    for (var i = 0; i < diseaseData.length; i++){
        disease = new Disease({
            _id: diseaseData[i].id,
            name: diseaseData[i].name,
            data_updated_at: diseaseData[i].data_updated_at,
            facts: diseaseData[i].facts,
            symptoms: diseaseData[i].symptoms,
            transmission: diseaseData[i].transmission,
            diagnosis: diseaseData[i].diagnosis,
            treatment: diseaseData[i].treatment,
            prevention: diseaseData[i].prevention,
            more: diseaseData[i].more
        });

        disease.save(function (err, response) {
            if(err){
                console.log(err);
            }else{
                console.log('Data Saved successfully');
            }
        })
    }
});

//retriving from database

diseaseschema.js

/**
 * Created by hydee on 1/16/17.
 */

const mongoose = require('mongoose');

mongoose.connect('mongodb://localhost/DiseaseDB');



var Disease = mongoose.model('Disease', {
    _id : Number,
    name: String,
    data_updated_at: String,
    facts: Array,
    symptoms: {
        type: String,
        default: null
    },
    transmission: {
        type: String,
        default: null
    },
    diagnosis: {
        type: String,
        default: null
    },
    treatment: {
        type: String,
        default: null
    },
    prevention: {
        type: String,
        default: null
    },
    more: {
        type: String,
        default: null
    }
});

module.exports = Disease

getDiseases.js

/**
 * Created by hydee on 1/16/17.
 */
const request = require('request');

var diseaseDetails = function(callback){

    request({
        url:'https://disease-info-api.herokuapp.com/diseases/',
        json:true
    }, function (error, response, body) {
        if (!error && response.statusCode == 200) {
            callback(body.diseases);
        }
    });
};

module.exports.diseaseDetails = diseaseDetails;

retrieve-data.js

var disease = require('./diseaseschema')


disease.findOne({name: "Rabies - WHO"}, function (err, response) {
    if(err){
        console.log(err);
    }else if(response){
        console.log(response);
    }else{
        console.log('Disease not found');
    }
});

I can't see your code ...

In app.js, the disease variable on line 5 is undefined initially. It could be defined and initialized within the for loop instead e.g.

for (var i = 0; i < diseaseData.length; i++){
        var disease = new Disease({
            _id: diseaseData[i].id,
            name: diseaseData[i].name,
            data_updated_at: diseaseData[i].data_updated_at,
            facts: diseaseData[i].facts,
            symptoms: diseaseData[i].symptoms,
            transmission: diseaseData[i].transmission,
            diagnosis: diseaseData[i].diagnosis,
            treatment: diseaseData[i].treatment,
            prevention: diseaseData[i].prevention,
            more: diseaseData[i].more
        });

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