Gain insights into MongoDB's core concepts, including queries, CRUD operations, aggregation, and more. Discover how to build applications with hands-on experience and interactive widgets.

mongo.tar.gz

MongoDB is an open-source NoSQL database and stores data in the form of documents. It can be used as an alternative to traditional relational databases. NoSQL databases are schema-less and useful for working with large sets of distributed data. 

In this course, you will learn the core concepts of MongoDB including queries, documents, embedded documents, and operators with advanced features like CRUD operations, bulk write operations, GridFS, indexing, aggregation pipeline, authorization, and more.

You will have plenty of hands-on experience with the help of interactive widgets, and by the end you will have a strong understanding of how to build MongoDB-based applications.

MongoDB: The Complete Guide

## `$lookup` stage

We use the **`$lookup`** stage to perform the join operations with other collections. This stage performs a left outer join for each input document, and adds a new `array` field where the results for the join are added. Next, the transformed documents are sent to the next stage.

We use the below syntax to define the `$lookup` stage.

```bash
{
    $lookup: {
        from: <target collection to join to>,
        localField: <field of the source document>,
				foreignField: <field of the target collection>,
        let: <variables to use in pipeline>,
        pipeline: <pipeline result is returned on out field>,
        as: <output field name>
    }
 }
```

To perform the `$lookup` stage, we need another collection that will have some referenced data in it. We insert some data into the `users` collection.

# `$lookup` stage

We use the **`$lookup`** stage to perform the join operations with other collections. This stage performs a left outer join for each input document, and adds a new `array` field where the results for the join are added. Next, the transformed documents are sent to the next stage.

We use the below syntax to define the `$lookup` stage.

```bash
{
    $lookup: {
        from: <target collection to join to>,
        localField: <field of the source document>,
				foreignField: <field of the target collection>,
        let: <variables to use in pipeline>,
        pipeline: <pipeline result is returned on out field>,
        as: <output field name>
    }
 }
```

To perform the `$lookup` stage, we need another collection that will have some referenced data in it. We insert some data into the `users` collection.

# `＄lookup` stage

We use the **`＄lookup`** stage to perform the join operations with other collections. This stage performs a left outer join for each input document, and adds a new `array` field where the results for the join are added. Next, the transformed documents are sent to the next stage.

We use the below syntax to define the `＄lookup` stage.

```bash
{
    $lookup: {
        from: <target collection to join to>,
        localField: <field of the source document>,
				foreignField: <field of the target collection>,
        let: <variables to use in pipeline>,
        pipeline: <pipeline result is returned on out field>,
        as: <output field name>
    }
 }
```

To perform the `＄lookup` stage, we need another collection that will have some referenced data in it. We insert some data into the `users` collection.

Learn and practice the $project, $limit, and $sort aggregation pipelines stages.

Introduction to Database and MongoDB

Create Database and Authorization

Performing CRUD Operations on MongoDB - Part 1

Performing CRUD Operations on MongoDB - Part 2

MongoDB Query and Database Performance

Learn Additional MongoDB Topics

Appendix

Aggregation Pipeline: Part 2

`$lookup` stage