$slice - Amazon DocumentDB (original) (raw)

The $slice projection operator limits the number of array elements returned in a query result. It allows you to retrieve a specific number of elements from the start or end of an array field without loading the entire array.

Parameters

• field: The array field to project.
• count: Number of elements to return. Positive values return elements from the start, negative values from the end.

Example (MongoDB Shell)

The following example demonstrates how to use the $slice projection operator to return only the first two items from an array field.

Create sample documents

db.inventory.insertMany([
  { _id: 1, item: "notebook", tags: ["office", "school", "supplies", "writing"] },
  { _id: 2, item: "pen", tags: ["office", "writing"] },
  { _id: 3, item: "folder", tags: ["office", "supplies", "storage", "organization"] }
]);

Query example

db.inventory.find(
  {},
  { item: 1, tags: { $slice: 2 } }
)

Output

{ "_id" : 1, "item" : "notebook", "tags" : [ "office", "school" ] }
{ "_id" : 2, "item" : "pen", "tags" : [ "office", "writing" ] }
{ "_id" : 3, "item" : "folder", "tags" : [ "office", "supplies" ] }

Code examples

To view a code example for using the $slice projection operator, choose the tab for the language that you want to use:

Node.js

const { MongoClient } = require('mongodb');

async function example() {
  const client = await MongoClient.connect('mongodb://<username>:<password>@<cluster-endpoint>:27017/?tls=true&tlsCAFile=global-bundle.pem&replicaSet=rs0&readPreference=secondaryPreferred&retryWrites=false');
  const db = client.db('test');
  const collection = db.collection('inventory');

  const result = await collection.find(
    {},
    { projection: { item: 1, tags: { $slice: 2 } } }
  ).toArray();

  console.log(JSON.stringify(result, null, 2));
  await client.close();
}

example();

Python

from pymongo import MongoClient

def example():
    client = MongoClient('mongodb://<username>:<password>@<cluster-endpoint>:27017/?tls=true&tlsCAFile=global-bundle.pem&replicaSet=rs0&readPreference=secondaryPreferred&retryWrites=false')
    db = client['test']
    collection = db['inventory']

    result = list(collection.find(
        {},
        {'item': 1, 'tags': {'$slice': 2}}
    ))

    print(result)
    client.close()

example()