Retrieve a Random Document in MongoDB Using $sample

How to Retrieve a Random Document from MongoDB?

To retrieve a random document from a MongoDB collection, you can use the aggregation pipeline with the $sample stage. The $sample stage allows you to select a specified number of random documents from a collection, making it ideal for scenarios where you need a randomized subset or a single random record.

In MongoDB, you can fetch a random document by using the $sample stage in an aggregation pipeline. The $sample stage randomly selects a specified number of documents from the collection, providing an efficient and easy way to retrieve a random record. This approach is particularly useful for sampling data, showing a random item, or testing purposes.

Syntax:

To get a random record from a MongoDB collection, use the following syntax:

db.<collection>.aggregate([
  { $sample: { size: 1 } }
])

Explanation:

• <collection>: The collection from which you want to retrieve a random document.
• size: The number of random documents you want to return. Set size to 1 to retrieve a single random document.

Example:

Suppose you have a products collection and want to fetch a single random product document:

Code:

// Use the aggregation pipeline to retrieve one random document from the products collection
db.products.aggregate([
  { $sample: { size: 1 } } // Select a single random document
])

Explanation:

• db.products.aggregate(...)
  This command initiates an aggregation pipeline on the products collection, which allows for advanced data processing and transformations.
• { $sample: { size: 1 } }
  The $sample stage is used to retrieve random documents. The size parameter is set to 1, indicating that we want one random document. Increasing size will fetch more random documents as a sample from the collection.

The aggregation pipeline processes this query and returns a randomly selected document from the products collection. This approach is efficient because $sample is optimized for random selection, making it suitable for large collections as well.

Additional Options:

If you need more than one random document, simply adjust the size parameter. For example, setting { size: 5 } will retrieve five random documents.

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