C100DEV Data Modeling Practice Question
Exhibit
{
"_id": "order_101",
"customer_name": "John Doe",
"shipping_address": "123 Main St",
"tax_rate": 0.08,
"total_price": 108.00
}Refer to the exhibit. Which design pattern is used to store 'total_price' in the document?
⚠ Common exam trap
Candidates often assume totals or aggregations should always be calculated dynamically on read, forgetting the heavy performance toll in read-heavy systems.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The Computed pattern.
This is the Computed pattern. By storing the final total in the document, the application avoids recalculating it during every read request. This is particularly valuable in heavy read-heavy applications where the cost of performing arithmetic aggregations across multiple documents is significantly higher than the cost of updating a pre-computed value during the initial write operation. It optimizes read performance at the expense of write complexity.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
The Subset pattern.
Why it's wrong here
The Subset pattern involves keeping only a small amount of data in the main document to ensure it stays small. While the exhibit is small, the presence of a calculated total suggests a focus on performance optimization for reads rather than just keeping document size under control.
- ✓
The Computed pattern.
Why this is correct
The Computed pattern stores calculated results directly in the document, which speeds up read operations. By avoiding complex aggregations during queries, the application serves data much faster. This pattern is commonly used for values like totals, averages, or counts that are derived from other fields in the document.
- ✗
The Polymorphic pattern.
Why it's wrong here
The Polymorphic pattern is used when documents in a collection have similar but not identical structures. The exhibit shows a standard order document; there is no evidence of different document types being handled within the same collection or a need to support flexible schemas in the way described.
- ✗
The Schema Versioning pattern.
Why it's wrong here
The Schema Versioning pattern involves adding a version field to documents to manage updates to the schema over time. The exhibit lacks a version field and does not show any signs of a migration strategy, focusing instead on a specific field calculation, which is not the purpose of versioning.
About these practice questions
This C100DEV question is part of Courseiva's 259-question bank — original exam-style content with full explanations and wrong-answer analysis, never real exam questions or exam dumps. Learn why practice questions differ from exam dumps →
JA
Written and reviewed by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
Last reviewed September 2026 · checked against the official MongoDB exam blueprint
This C100DEV practice question is part of Courseiva's free MongoDB certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the C100DEV exam.