Query for documents where array size is greater than 1

How to Query for Documents Where Array Size is Greater Than 1 in MongoDB

Do you have a MongoDB collection with documents that contain arrays, and you want to query for documents where the array size is greater than 1? 🤔 In this blog post, we will address this common issue and provide you with easy solutions to get the results you need!

The Problem

Let's start by understanding the problem at hand. You have a MongoDB collection with documents in the following format:

{
  "_id" : ObjectId("4e8ae86d08101908e1000001"),
  "name" : ["Name"],
  "zipcode" : ["2223"]
},
{
  "_id" : ObjectId("4e8ae86d08101908e1000002"),
  "name" : ["Another ", "Name"],
  "zipcode" : ["2224"]
}

You want to query for documents where the name field has an array size greater than 1. You might naturally try the following query:

db.accommodations.find({ name : { $size : 2 }})

This works perfectly fine and returns the documents with 2 elements in the name array. However, when you try to use the $gt command to query for documents with a name array size greater than 1, you face an issue:

db.accommodations.find({ name : { $size: { $gt : 1 } }})

This query doesn't give the desired results, and you're left wondering how to select all documents with a name array of a size greater than one. And the cherry on top - you'd prefer not to modify the current data structure. 😫

The Solution

Don't worry! MongoDB has got you covered with the powerful aggregation framework! 🎉

To overcome the limitation of the $size operator, we can use the $expr operator along with the $gt operator in an aggregation pipeline. Here's how you can achieve this:

1. Use the $project stage to add a new field called nameSize that holds the size of the name array:

   db.accommodations.aggregate([ { $project: { _id: 1, name: 1, nameSize: { $size: "$name" } } } ])

   This will give you a result like this:

   { "_id" : ObjectId("4e8ae86d08101908e1000001"), "name" : ["Name"], "nameSize" : 1 }, { "_id" : ObjectId("4e8ae86d08101908e1000002"), "name" : ["Another ", "Name"], "nameSize" : 2 }

2. Add a $match stage to filter documents where nameSize is greater than 1:

   db.accommodations.aggregate([ { $project: { _id: 1, name: 1, nameSize: { $size: "$name" } } }, { $match: { nameSize: { $gt: 1 } } } ])

   This will give you the desired documents:

   { "_id" : ObjectId("4e8ae86d08101908e1000002"), "name" : ["Another ", "Name"], "nameSize" : 2 }

And voilà! You have successfully queried for documents where the name array has a size greater than 1 without modifying the current data structure. 🙌

Take It to the Next Level

Now that you know how to query for documents with an array size greater than 1, why not explore more about the MongoDB aggregation framework? You can unlock even more powerful querying capabilities and perform complex operations with ease.

Take a look at the official MongoDB documentation to dive deeper into the aggregation pipeline and unleash the full potential of MongoDB!

So what are you waiting for? Start querying those arrays and take control of your MongoDB data! Happy coding! 💻

Have any questions or additional tips? Share them in the comments below! Let's learn and grow together! 🚀