mongodb

name	mongodb
description	MongoDB — aggregation pipeline, indexes, schema design, Atlas Search, Mongoose ODM.

mongodb

Aggregation Pipeline

• Stages: $match (filter), $group (group by field), $sort, $project (shape docs).
• $lookup — join collections (left outer join with pipeline syntax).
• $unwind — deconstruct arrays; $addFields — computed fields.
• $facet — multi-faceted aggregation within a single pipeline.

Indexes

• Compound: db.collection.createIndex({ field1: 1, field2: -1 }).
• Text: createIndex({ content: "text" }) with $text search operator.
• Geospatial: 2dsphere indexes for GeoJSON queries.
• TTL indexes, sparse indexes, partial indexes for targeted workloads.

Schema Design

• Embedding for read-heavy, one-to-few relationships.
• Referencing for one-to-many/many-to-many with $lookup.
• Bucket pattern for time-series data; polymorphic pattern with discriminator fields.

Atlas Search / Vector

• $search aggregation stage — Lucene-based full-text search.
• Atlas Vector Search — $vectorSearch for semantic/kNN queries.
• Index configuration via Atlas UI or searchIndexes collection.

Mongoose ODM

• new Schema({ field: { type: String, required: true, index: true } }).
• Model.find(), .create(), .findByIdAndUpdate(), hooks (pre/post save).
• Virtuals, plugins, discriminators, custom validation.

Change Streams

• collection.watch() — real-time notifications on inserts, updates, deletes.
• Resume via resumeAfter token; use with $match filter for specific collections.

Transactions

• session.startTransaction() for multi-document ACID transactions.
• Retry logic on TransientTransactionError.