[Fixed] Mongoose always returns an empty array []

Understanding the Error

When Mongoose returns an empty array, it generally indicates that it is unable to find any documents in the requested collection that match the query parameters. This can occur for several reasons such as an incorrect query, a mismatch between the model and the actual database schema, an empty dataset in the database, or even syntactical issues that might not be immediately obvious.

Solutions

Check the Database Connection

First, ensure that your database connection is established correctly. A failed connection may not necessarily throw an error but could result in an empty query result. Look for connection success messages or explicitly handle the connection error.

Verify Collection Name and Schema

Next, match the collection name in your database with the name defined within your Mongoose Schema. Mongoose pluralizes the model name to form the collection name unless specified otherwise. Similarly, ensure that the schema defined in your model represents the structure of documents within your actual MongoDB collection.

Inspect the Query Criteria

Carefully inspect the query that you are running. Subtle typo in field names or incorrect logic can affect the result set. Use debugging techniques, such as console.logging the query criterion, to ensure that it represents the intended logic to match with the existing database entries.

Making Sure The Dataset Exists

It is possible that your query is syntactically correct, yet the collection doesn’t hold matching documents. You may want to inject sample data into your database and test the query against it.

Utilize Async/Await for Asynchronous Operations

Node.js is inherently asynchronous, and using the async/await syntax provided by JavaScript can help you handle asynchronous database operations more neatly. Ensure your function that calls the Mongoose method is marked ‘async’, and you use ‘await’ to wait for the result of your query.

A Code Example

Let’s examine a working example to learn to avoid the error:

import mongoose from 'mongoose';

const userSchema = new mongoose.Schema({
    name: String,
    age: Number
});
const User = mongoose.model('User', userSchema);

const retrieveUsers = async () => {
    try{
        await mongoose.connect('mongodb://localhost:27017/mydatabase');
        const users = await User.find({});
        console.log(users);
        mongoose.disconnect();
    } catch (error) {
        console.error('An error occurred:', error);
    }
};

retrieveUsers();

The above example defines a model representing a user schema and attempts to retrieve users from the MongoDB database named ‘mydatabase’. Importantly, it utilizes the async/await pattern for operations that return promises, such as establishing the database connection and querying the database.