MongoDB Associate Developer Study Guide Flashcards

Vocabulary flashcards covering core MongoDB concepts, BSON data types, CRUD operations, query operators, indexing, aggregation, data modeling, and driver usage.

BSON (Binary JSON)

A binary-encoded serialization format used by MongoDB to store documents, serving as a superset of JSON with more precise data types.

Double (BSON Type)

BSON's floating-point numerical data type; note that BSON refers to this type specifically as Double and not Float.

Decimal128

A BSON data type representing an exact decimal value, designated specifically for storing monetary values.

Date (BSON Type)

A BSON data type stored internally as milliseconds since the Unix epoch, represented in MQL as ISODate.

ObjectId

The default BSON type for the _id field, consisting of a 12-byte value that is roughly sortable by creation time.

MinKey / MaxKey

Special BSON types that compare lower or higher than all other BSON values, primarily utilized in database sharding.

Schema Flexibility

A MongoDB feature allowing individual documents within the same collection to contain different fields unless restricted by a $jsonSchema validator.

insertMany()

A CRUD insert method that takes an array of document objects to write into a collection, operating in ordered mode by default.

Ordered Insert

The default execution mode of insertMany(), where an error inserting a document halts processing for all remaining documents in the array unless { ordered: false } is set.

Full Document Replacement

The outcome of updating a document using replaceOne() or passing a bare document object without $ update operators, which completely replaces all fields except _id.

$set

A surgical update operator that modifies or adds only the specified fields or path names while preserving all untouched fields in the document.

$inc

An update operator used to increment or decrement a numeric field by a specified value.

$addToSet

An update operator that appends a value to an array field only if the specified value does not already exist in the array.

Upsert

An update option ({ upsert: true }) that updates a matching document, or creates a new document combining the filter's equality fields and the update fields if no match exists.

findOneAndUpdate()

An atomic find-and-modify operation that performs matching and updating in a single indivisible step, preventing concurrency issues like race conditions.

deleteOne() vs. deleteMany()

deleteOne() removes only the first document that satisfies the given filter, whereas deleteMany() removes all documents matching the filter.

$elemMatch

A query operator that evaluates array elements, requiring at least one single array element to satisfy all specified query conditions.

Implicit AND

Query evaluation where multiple field conditions specified within a single filter object are automatically combined with logical AND logic.

$or

A logical query operator that takes an array of expressions and matches documents satisfying at least one of those conditions.

Projection

A query parameter controlling field visibility in output documents, where mixing 1s (inclusion) and 0s (exclusion) in a single projection is invalid except when excluding _id.

countDocuments() vs. estimatedDocumentCount()

countDocuments() returns an exact count of documents matching a filter, whereas estimatedDocumentCount() provides a fast estimate based on collection metadata without supporting filters.

$search

An aggregation pipeline stage used for MongoDB Atlas Search full-text queries, which must be positioned as the pipeline's first stage and requires an Atlas Search Index.

$group

An aggregation pipeline stage that separates documents into groups according to a specified _id expression and computes aggregate accumulator values ($sum, $avg, $max, $min, $push) per group.

$lookup

An aggregation stage performing an equality left outer join between documents from an input collection and an unjoined collection, outputting matching documents as an array.

$out

An aggregation pipeline stage that writes pipeline output documents to a target collection, completely replacing any existing data in that destination collection.

COLLSCAN vs. IXSCAN

Execution plan stages in explain() output where COLLSCAN indicates a full collection scan and IXSCAN indicates an indexed scan.

Embed vs. Reference

Data modeling strategies where child data is placed inside the main document as sub-documents/arrays (Embed) or stored separately in a different collection linked via _id (Reference).

Unbounded Array Anti-Pattern

A database design anti-pattern where an array field grows indefinitely, risking exceeding MongoDB's 16MB document size limit and causing degraded performance.

mongodb+srv://

A connection URI protocol scheme that performs DNS SRV lookups to establish connections to MongoDB Atlas clusters.

MQL vs. Aggregation Framework

MQL find() processes a single filter object to filter, project, sort, and limit documents, while aggregate() uses an array of stage objects to perform complex operations like grouping and joins.