Replace the entire config document `_id: 1` with `{ _id: 1, theme: "dark", lang: "en" }`. Return all configs.

Problem Statement

<p>Replace the entire config document <code>_id: 1</code> with <code>{ <code>_id</code>: 1, theme: "dark", lang: "en" }</code>. Return all configs.</p>

Examples

Input: configs collection: +-----+-------+------+----------+ | _id | theme | lang | fontSize | +-----+-------+------+----------+ | 1 | light | fr | 14 | | 2 | dark | en | 16 | +-----+-------+------+----------+

Output: +-----+-------+------+----------+ | _id | theme | lang | fontSize | +-----+-------+------+----------+ | 1 | dark | en | null | | 2 | dark | en | 16 | +-----+-------+------+----------+

Explanation: The query retrieves all documents from the collection that satisfy the specified filter criteria.

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 "Replace a Document (replaceOne)", we query the MongoDB document store. The goal is to replace the entire config document `_id: 1` with `{ _id: 1, theme: "dark", lang: "en" }`. return all configs. 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.configs.replaceOne({ _id: 1 }, { theme: "dark", lang: "en" });
  return db.configs.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.

Replace a Document (replaceOne)

Easy

Replace the entire config document _id: 1 with { _id: 1, theme: "dark", lang: "en" }. Return all configs.

Example Scenarios

1Example 1

Input:

configs collection

_id	theme	lang	fontSize
1	light	fr	14
2	dark	en	16

Output:

_id	theme	lang	fontSize
1	dark	en	null
2	dark	en	16

Explanation:

The query retrieves all documents from the collection that satisfy the specified filter criteria.

MongoDB Editor

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Query Results (JSON)

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