Add the role `"viewer"` to ALL users `permissions` arrays without duplicating. Return all users.

Problem Statement

<p>Add the role <code>"viewer"</code> to ALL <code>users</code> <code>permissions</code> arrays without duplicating. Return all <code>users</code>.</p>

Examples

Input: users collection: +-----+---------+--------------------+ | _id | name | permissions | +-----+---------+--------------------+ | 1 | Alice | ["admin","viewer"] | | 2 | Bob | ["editor"] | | 3 | Charlie | [] | +-----+---------+--------------------+

Output: +-----+---------+---------------------+ | _id | name | permissions | +-----+---------+---------------------+ | 1 | Alice | ["admin","viewer"] | | 2 | Bob | ["editor","viewer"] | | 3 | Charlie | ["viewer"] | +-----+---------+---------------------+

Explanation: The target document is modified according to the update operators and the updated document is returned.

Complexity

Time Complexity: -

Space Complexity: -

Hints

💡 Hint 1: Use db.<collection>.find(<filter>) to query the documents in the collection. 💡 Hint 2: Pass an empty object {} to retrieve all documents, or specify key-value pairs for exact matching. 💡 Hint 3: Chain .toArray() to resolve the MongoDB cursor into a JavaScript array: return db.<collection>.find(...).toArray();

Editorial & Approach

Problem Overview & Intuition

To solve "AddToSet on Multiple Documents", we query the MongoDB document store. The goal is to add the role `"viewer"` to all users `permissions` arrays without duplicating. return all users. Using a targeted find query, the database engine filters and structures the BSON documents efficiently.

Step-by-Step Approach

Identify Target Collection: Access the collection through the db instance.
Construct Query / Pipeline: Build the query filter with appropriate comparison operators.
Resolve Cursor: Invoke .toArray() to transform the query cursor into the required array of documents.

Optimal Implementation (MongoDB)

function solve(db) {
  db.users.updateMany({}, { $addToSet: { permissions: "viewer" } });
  return db.users.find({}).toArray();
}

Complexity Analysis

Time Complexity O(N) collection scan (O(log N) if index is present on filtered fields).

Space Complexity O(K) where K is the number of returned documents in memory.

Key Considerations & Edge Cases

Empty Collections: If no documents match, the query cleanly returns an empty array [].
Missing / NULL Fields: Missing fields in documents are handled safely without throwing runtime exceptions.
Type Coercion: BSON types (ObjectId, Numbers, Strings) are compared strictly according to MongoDB specifications.

AddToSet on Multiple Documents

Medium

Add the role "viewer" to ALL users permissions arrays without duplicating. Return all users.

Example Scenarios

1Example 1

Input:

users collection

_id	name	permissions
1	Alice	["admin","viewer"]
2	Bob	["editor"]
3	Charlie	[]

Output:

_id	name	permissions
1	Alice	["admin","viewer"]
2	Bob	["editor","viewer"]
3	Charlie	["viewer"]

Explanation:

The target document is modified according to the update operators and the updated document is returned.

MongoDB Editor

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Query Results (JSON)

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