Delete all expired sessions (`expired: true`) from the `sessions` collection. Return remaining sessions.

Problem Statement

<p>Delete all expired <code>sessions</code> (<code>expired: true</code>) from the <code>sessions</code> collection. Return remaining <code>sessions</code>.</p>

Examples

Input: sessions collection: +-----+--------+---------+ | _id | userId | expired | +-----+--------+---------+ | 1 | u1 | false | | 2 | u2 | true | | 3 | u3 | true | | 4 | u4 | false | +-----+--------+---------+

Output: +-----+--------+---------+ | _id | userId | expired | +-----+--------+---------+ | 1 | u1 | false | | 4 | u4 | false | +-----+--------+---------+

Explanation: The matching documents are removed from the collection and the remaining count is verified.

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 "Delete Many Documents (deleteMany)", we query the MongoDB document store. The goal is to delete all expired sessions (`expired: true`) from the `sessions` collection. return remaining sessions. 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.sessions.deleteMany({ expired: true });
  return db.sessions.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.

Delete Many Documents (deleteMany)

Easy

Delete all expired sessions (expired: true) from the sessions collection. Return remaining sessions.

Example Scenarios

1Example 1

Input:

sessions collection

_id	userId	expired
1	u1	false
2	u2	true
3	u3	true
4	u4	false

Output:

_id	userId	expired
1	u1	false
4	u4	false

Explanation:

The matching documents are removed from the collection and the remaining count is verified.

MongoDB Editor

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Query Results (JSON)

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