NodeJS RESTful API Import/Require dilemma

Question

I'm currently working on my first node.js/express rest API and I ran into an issue.

I use mongoose to build Schemas, and one of those Schemas requires data (for validation porpuses) from its origin DataBase.

Now I have an import dilemma because at the time I import the Schemas, there is not yet a binding to the DataBase. I tried to import the models from server.js to request Data from the DB. However, I got an error that the model I tried to import is undefined. Hence the Connection to the DB in server.js is not yet established at the time of import.

This here is my server.js , I require the Schemas from ./api/models/newsClassificationHubModel As you can see at the time I import the Schemas I didn't establish the required connection.

//server.js

const express = require("express"),
    app = express(),
    port = process.env.PORT || 3000,
    mongoose = require("mongoose"),
    schemas = require("./api/models/newsClassificationHubModel"),
    bodyParser = require("body-parser");

// mongoose instance connection url
mongoose.Promise = global.Promise;
TagHubClusterConnection = mongoose.createConnection("mongodb+srv://admin:##########@cluster0.yzl7d.mongodb.net/textClassHub?retryWrites=true&w=majority\n",
    { useNewUrlParser: true, useUnifiedTopology: true });

// export models with custom connections
exports.devSentence = TagHubClusterConnection.model("newSentence_DB", schemas.registerNewSentence)
exports.devTagBase = TagHubClusterConnection.model("baseTag_DB", schemas.registerNewBaseTag)
exports.devTagChild = TagHubClusterConnection.model("childTag_DB", schemas.registerNewChildTag)

app.use(bodyParser.urlencoded({extended: true}));
app.use(bodyParser.json());

const routes = require("./api/routes/newsClassHubRoutes");
routes(app); // register the route

app.listen(port, "localhost",function() {
    console.log("server is listening on http://localhost:" + port)
})

Here you can see a shortened version of the Schema defenition in ./api/models/newsClassificationHubModel , At this point, I would need to do a request to the DB to get the valid tags from the DB

// newsClassificationHubModel.js (Schemas) 

const mongoose = require("mongoose");
const Schema = mongoose.Schema;

// get validTags from DB
let validTags = []


// Schema definition
const registerNewChildTag = new Schema({
    tagID: {
        type: String,
        required: true
    },
    tagName: {
        type: String,
        required: true
    },
    description: {
        type: String,
        validate: [lengthValidator, "Please enter a description with min 30 characters"],
        required: true
    },
    childTag: {
        type: String,
        enum: {
            values: validTags,
            message: "Please enter a valid tagID"
        },
        required: true
    }
});

exports.registerNewChildTag = mongoose.model("childTag_DB", registerNewChildTag);

I believe I could use A promise to solve that problem, yet I don't know how to do it exactly.

I appreciate any hint from anyone, and If something is unclear please don't hesitate to ask for a better explanation

BreadBerry

Answer 1

The problem you have here is that when you import the schema file tries to create a model but there is no connection yet for the app. I think it will work if you move your import down after creating the connection. also importing your models inside the server file is not the best practice.