Lookup (Joins)

Perform lookups (joins) on your collections.

Before we get started, please review the Lookup Pipeline documentation.

Method Signature

public lookup(options: LookupPipelineOptions): this;

Where LookupOptions is:

export type LookupPipelineOptions = {
  from: string;
  localField?: string;
  foreignField?: string;
  as?: string;
  single?: boolean;
  pipeline?: (Pipeline | GenericObject)[];
  let?: GenericObject;
};

Example

Let's see a basic example, let's see we need to load posts with the updated data of the authors from users collection.

const posts = await new Aggregate("posts")
  .lookup({
    from: "users",
    localField: "author.id",
    foreignField: "id",
    as: "author",
    single: true,
  })
  .get();

By adding single option, it will return the first document in the array.

Lookup with multiple documents

Let's load posts with their comments.

const posts = await new Aggregate("posts")
  .lookup({
    from: "comments",
    localField: "id",
    foreignField: "postId",
    as: "comments",
  })
  .get();

This will load with each post all the comments that belong to it.

Lookup with pipeline

Let's load posts with their comments, but we want to load only the comments that have more than 10 likes.

const posts = await new Aggregate("posts")
  .lookup({
    from: "comments",
    localField: "id",
    foreignField: "postId",
    as: "comments",
    pipeline: [
      {
        $match: {
          likes: {
            $gt: 10,
          },
        },
      },
    ],
  })
  .get();

Calling MongoDB Aggregate stages

Most of MongoDB Aggregate stages are exported separately, so we can use them directly in the pipelines.

Let's load posts with their comments, but we want to load only the comments that have more than 10 likes.

import { wherePipeline, parsePipelines } from "@mongez/monpulse";

const posts = await new Aggregate("posts")
  .lookup({
    from: "comments",
    localField: "id",
    foreignField: "postId",
    as: "comments",
    pipeline: parsePipelines([wherePipeline("likes", ">", 10)]),
  })
  .get();

Available stages to use

Here are the available stages to use with parsePipelines function:

• wherePipeline: Receives same arguments as where method.
• limitPipeline: Receives same arguments as limit method.
• skipPipeline: Receives same arguments as skip method.
• sortPipeline: Receives same arguments as sort method.
• sortByPipeline: Receives same arguments as sortBy method.
• sortRandomPipeline: Receives same arguments as random method.
• selectPipeline: Receives same arguments as select method.
• deselectPipeline: Receives same arguments as deselect method.
• groupByPipeline: Receives same arguments as groupBy method.
• lookupPipeline: Receives same arguments as lookup method.
• orWherePipeline: Receives same arguments as orWhere method.
• unwindPipeline: Receives same arguments as unwind method.

Lookup with let

Let's load posts with their comments, but we want to load only the comments that have more than 10 likes.

const posts = await new Aggregate("posts")
  .lookup({
    from: "comments",
    localField: "id",
    foreignField: "postId",
    as: "comments",
    let: {
      postId: "$id",
    },
    pipeline: [
      {
        $match: {
          $expr: {
            $and: [
              {
                $eq: ["$postId", "$$postId"],
              },
              {
                $gt: ["$likes", 10],
              },
            ],
          },
        },
      },
    ],
  })
  .get();

This is just the native MongoDB syntax, you can use it directly in the pipeline option.