How to query data in mongodb

MongoDB data query can use the following commands: find(): query documents based on conditions. Query conditions: Specify conditions, such as document attributes, arrays, etc. Projection: Specify the return field, such as { title: 1, author: 1 }. Sorting: Specify the sorting field and order, such as { publishedDate: 1 }. Limit: Specify the number of documents returned, such as limit(5).

MongoDB data query

Data query in MongoDB can be performed through the following command:

find()

find() command is used to search for documents that meet specific conditions. The syntax is:

<code>db.collection.find({ <查询条件> })</code>

Query conditions

Query conditions specify the conditions of the document to be found. Query conditions can be document attributes, arrays, nested documents, or other complex conditions.

Example:

Find documents whose title contains "MongoDB":

<code>db.articles.find({ title: /MongoDB/ })</code>

Find documents whose author is "John Doe":

<code>db.articles.find({ author: "John Doe" })</code>

Projection

Projection specifies the fields contained in the document to be returned. The syntax is:

<code>db.collection.find({ <查询条件> }, { <投影条件> })</code>

Projection conditions

Projection conditions specify the fields to be returned or excluded.

Example:

Return only the fields of title and author:

<code>db.articles.find({}, { title: 1, author: 1 })</code>

Sort

Sort specified The field by which to sort the documents. The syntax is:

<code>db.collection.find({ <查询条件> }).sort({ <排序条件> })</code>

Sort conditions

Sort conditions specify the sort order of fields. 1 means ascending order, -1 means descending order.

Example:

Sort in ascending order by release date:

<code>db.articles.find({}).sort({ publishedDate: 1 })</code>

Limitations

Limitations specify what to return number of documents. The syntax is:

<code>db.collection.find({ <查询条件> }).limit(<数量>)</code>

Example:

Limit the first 5 documents returned:

<code>db.articles.find({}).limit(5)</code>

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