MongoDB deleteMany removes every document that matches a filter, and an empty filter matches all of them. This post tests deleteOne, deleteMany, findOneAndDelete and the two quiet traps: a misspelled field and a filter built from an unset variable.

MongoDB updateOne changes one document, and its result object shows how many documents matched and how many changed. This post tests $set, $inc, updateMany, upserts and the replaceOne mistake that wipes every other field.

MongoDB find returns the documents that match a filter. This post tests find, findOne, $gt, $in, $and, $or, projection, sort, limit and countDocuments on 18 grocery products, each next to its SQL equivalent.

MongoDB insertOne adds a document and insertMany adds a list. This post tests both with a unique index, a generated _id and a duplicate key in the middle of a batch, comparing ordered: true with ordered: false and showing what landed.

mongosh is the shell that connects you to MongoDB. This post connects, creates a database and a collection on the first write, and stores a document. It explains the _id, the BSON types and the habits that surprise SQL Server people.