db-mongodb

# AI Skill: MongoDB Engineering and Administration (db-mongodb) This skill guides the artificial intelligence to act as a specialist in the document-oriented **MongoDB** database, grounded in the official documentation ([mongodb.com/pt-br/docs](https://www.mongodb.com/pt-br/docs/)). It covers advanced schema-modeling strategies, the WiredTiger storage engine, consistency guarantees (Write/Read Concern), index optimization, the Aggregation Framework, Replica Sets, and Sharded Clusters. --- ## 🧭 Document-Oriented Data Modeling In MongoDB, modeling is driven by the application's access patterns (read and write queries together), rather than by strict normalization: ### 1. Embedding vs. Referencing - **Embed (Denormalization - Preferred)**: - Use when there are 1:1 or 1:N relationships (where N is bounded and small, e.g. a customer's addresses). - Guarantees write atomicity and high-performance reads in a single I/O operation. - **Reference (Normalization)**: - Use when there are 1:N relationships (where N is unbounded or very large, e.g. audit logs) or N:M relationships. - Avoids the maximum BSON document size limit (16 MB). ### 2. Schema Design Patterns - **Subset Pattern**: Keeps only the N most recent or most accessed data in the main document and the rest in a separate collection. - **Bucket Pattern**: Groups time-series data or IoT metrics into time windows (e.g. 1 hour) to reduce the number of documents and optimize indexes. - **Outlier Pattern**: Handles exceptionally large documents separately without penalizing the majority of standard documents. --- ## 🛠️ Advanced Indexing and Query Optimization ### 1. Index Types in MongoDB - **Compound Index**: Follow the ESR rule (**Equality, Sort, Range**): - 1st: Exact-equality fields (`$eq`). - 2nd: Fields used for sorting (`sort()`). - 3rd: Range fields (`$gte`, `$lte`, `$in`). - **Multikey Index**: Created automatically when indexing fields that contain arrays. - **TTL Index**: Automatically deletes documents after a specified time: ```javascript db.sessions.createIndex({ "createdAt": 1 }, { expireAfterSeconds: 3600 }); ``` - **Geospatial (`2dsphere`)**: For proximity queries (`$near`, `$geoWithin`). ### 2. Analysis with `explain()` Always run the explanation in `executionStats` mode to diagnose collection scans (*COLLSCAN*): ```javascript db.orders.explain("executionStats").find({ status: "COMPLETED", createdAt: { $gte: ISODate("2026-01-01") } }); ``` --- ## 🔍 Native Aggregation Framework Use aggregation pipelines for complex data transformations natively and in parallel: ```javascript db.orders.aggregate([ // 1. Initial filtering using an index { $match: { status: "COMPLETED", orderDate: { $gte: ISODate("2026-01-01") } } }, // 2. Join with the customers collection { $lookup: { from: "customers", localField: "customerId", foreignField: "_id", as: "customer_details" } }, // 3. Flatten the array generated by the lookup { $unwind: "$customer_details" }, // 4. Grouping and metric calculation { $group: { _id: "$customer_details.segment", totalRevenue: { $sum: "$totalAmount" }, averageOrderValue: { $avg: "$totalAmount" }, totalOrders: { $count: {} } } }, // 5. Sorting the result { $sort: { totalRevenue: -1 } } ]); ``` --- ## ⚙️ Concurrency, Consistency, and High Availability ### 1. Consistency and Durability Guarantees - **Write Concern**: Controls write acknowledgment by the cluster: - `w: "majority"`: Guarantees the write was persisted to the journal of the majority of Replica Set nodes (prevents *rollback* on failover). - **Read Concern**: - `rc: "majority"`: Returns only data confirmed by the majority of nodes. - `rc: "linearizable"`: Guarantees strictly real-time reads (avoids stale reads). ### 2. Production Architecture - **Replica Sets**: A minimum of 3 voting nodes (1 Primary and 2 Secondary) to automate election and failover without downtime. - **Sharded Cluster**: For horizontal scalability across multiple terabytes of data. Choose the **Shard Key** carefully to avoid *jumbo chunks* or write hotspots. --- ## 🔒 Hardening and Security Compliance (OWASP ASVS & CIS MongoDB Benchmark) - **Mandatory Authentication and TLS**: - Enable access-control authentication (`security.authorization: enabled`). - Require encrypted TLS 1.3/1.2 connections (`net.tls.mode: requireTLS`). - **Internal Cluster Authentication**: Use X.509 certificates or a keyfile for communication between Replica Set or Shard nodes. - **Client-Side Field Level Encryption (CSFLE)**: Encrypt sensitive data (PII, card numbers) on the client side using KMS keys before transmission to the database. - **Schema Validation (`$jsonSchema`)**: Apply Schema Validation on the collection to prevent NoSQL operator injection (`$where`, `$gt: ""`). --- ## 🔗 Integration with Other Skills - To integrate MongoDB into Node.js/TypeScript or Python APIs, see [backend-developer](../../roles/backend-developer/SKILL.md), [lang-typescript](../../languages/lang-typescript/SKILL.md), and [lang-python](../../languages/lang-python/SKILL.md). - For general administration guidelines for NoSQL and SQL databases, see [dba-database-administrator](../../roles/dba-database-administrator/SKILL.md). - For data security and compliance validation (V8/V14), see [appsec-owasp-asvs](../../security/appsec/appsec-owasp-asvs/SKILL.md), [cis-controls](../../security/grc/cis-controls/SKILL.md), and [security-privacy](../../security/grc/security-privacy/SKILL.md).