MongoDB 面试题与答案
问题 21. What is the role of the `$lookup` stage in MongoDB aggregation?
The `$lookup` stage is used in MongoDB aggregation to perform a left outer join between documents from the source and target collections based on a specified condition.
问题 22. How can you create an index in MongoDB?
You can create an index in MongoDB using the `createIndex` method. For example, `db.collection.createIndex({ field: 1 })` creates an ascending index on the specified field.
问题 23. What is the use of the `mongostat` command in MongoDB?
The `mongostat` command provides a real-time view of various MongoDB statistics, such as insert and query rates, memory usage, and more.
问题 24. What is the purpose of the `findOne` method in MongoDB?
The `findOne` method in MongoDB is used to retrieve a single document that satisfies the specified query criteria. It returns the first document that matches the query.
问题 25. How does MongoDB handle transactions?
MongoDB supports multi-document transactions starting from version 4.0. Transactions allow you to perform multiple operations on one or more documents and ensure atomicity and consistency.
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