Find all book loans where `returned` is `false` and `dueDate` is less than `20260715`. Sort by dueDate ascending.

Problem Statement

<p>Find all book loans where <code>returned</code> is <code>false</code> and <code>dueDate</code> is less than <code>20260715</code>. Sort by dueDate ascending.</p>

Examples

Input: loans collection: +-----+---------------+--------+----------+----------+ | _id | book | member | returned | dueDate | +-----+---------------+--------+----------+----------+ | 1 | MongoDB Guide | A | false | 20260710 | | 2 | Node.js | B | true | 20260712 | | 3 | React | C | false | 20260720 | | 4 | Python | D | false | 20260701 | +-----+---------------+--------+----------+----------+

Output: +-----+---------------+--------+----------+----------+ | _id | book | member | returned | dueDate | +-----+---------------+--------+----------+----------+ | 4 | Python | D | false | 20260701 | | 1 | MongoDB Guide | A | false | 20260710 | +-----+---------------+--------+----------+----------+

Explanation: Documents containing the matching array elements are selected from the collection.

Complexity

Time Complexity: -

Space Complexity: -

Hints

💡 Hint 1: Use comparison operators ($gt, $gte, $lt, $lte) to filter documents based on numeric or date ranges. 💡 Hint 2: Construct the filter condition: { fieldName: { $gt: value } } inside db.<collection>.find(...). 💡 Hint 3: Chain projection or sorting if requested, and invoke .toArray() to produce the result array.

Editorial & Approach

Problem Overview & Intuition

To solve "Library: Overdue Book Finder", we query the MongoDB document store. The goal is to find all book loans where `returned` is `false` and `duedate` is less than `20260715`. sort by duedate ascending. 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) {
  return db.loans.find({ returned: false, dueDate: { $lt: 20260715 } }).sort({ dueDate: 1 }).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.

Library: Overdue Book Finder

Hard

Find all book loans where returned is false and dueDate is less than 20260715. Sort by dueDate ascending.

Example Scenarios

1Example 1

Input:

loans collection

_id	book	member	returned	dueDate
1	MongoDB Guide	A	false	20260710
2	Node.js	B	true	20260712
3	React	C	false	20260720
4	Python	D	false	20260701

Output:

_id	book	member	returned	dueDate
4	Python	D	false	20260701
1	MongoDB Guide	A	false	20260710

Explanation:

Documents containing the matching array elements are selected from the collection.

MongoDB Editor

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Query Results (JSON)

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