How to Use MongoDB's $week Operator in Conjunction with Java's Calendar.WEEK_OF_YEAR

What is the relationship between MongoDB's $week operator and Java's Calendar.WEEK_OF_YEAR?

// Java code example for getting the week of the year
Calendar calendar = Calendar.getInstance();
calendar.set(2023, Calendar.JANUARY, 1);
int weekOfYear = calendar.get(Calendar.WEEK_OF_YEAR); // Returns 52 for 2023

This guide explains how MongoDB's $week aggregation operator relates to Java's Calendar.WEEK_OF_YEAR constant, detailing their usage in applications that require date manipulation.

// MongoDB query example to extract week of year from date
db.collection.aggregate([
  { $project: { weekOfYear: { $week: '$dateField' } } }
]);

Causes

• MongoDB uses $week to extract the week number from date objects.
• Java's Calendar class utilizes the WEEK_OF_YEAR constant to retrieve the week number of a specified date.

Solutions

• When extracting week numbers from date entries, ensure both systems follow the same week-start conventions (e.g., Monday vs. Sunday).
• Utilize the same date formats and time zones in both MongoDB queries and Java applications to maintain consistency.

Mistake: Not aligning the week start day between MongoDB and Java, leading to discrepancies in week numbers.

Solution: Use the same settings in both MongoDB and Java for week start to prevent inconsistencies.

Mistake: Using different date formats in MongoDB and Java applications, which may produce unexpected results.

Solution: Always standardize date formats (e.g., ISODate) across both platforms.