Brief introduction to MongoDB conditional query instances

For example, you can query users whose age is greater than or equal to 20 and whose age is less than 30.

Example

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Db. user. find ({"age": {"$ gte": 20, "$ lt": 30 }})

Or query. To query multiple values of a key, for example, if the age is, you can use the $ in operator:

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Db. user. find ({"age": {"$ in": [18, 20]});

If $ nin is used above, it means that age is not equal to 18 or 20.
To match multiple keys, you need the $ or operator, for example, query age = 18 or sex = female.

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Db. user. find ({"$ or": [{"age": 18 },{ "sex": "female"}]});

$ Mode is a special operator. For example, to retrieve all users with snakes, the 2013 operator means age % 12 = 0.

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Db. user. find ({"age": {"$ mod": [12, 0]})

The $ not operator can be used on any condition, for example, to identify non-snake users:

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Db. user. find ({"age": {"$ not": {"$ mod": [12, 0]})

In addition, find also supports regular expressions:

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Db. user. find ({"name ":/. * j. */I}) db. user. find ({"name ":/. * j. */I })

The above rule matches records with j in all user names. Note that regular expressions do not need to be enclosed by double quotation marks.

You can use the $ elemMatch operator to query the attributes of a document. For example, if the post set comment title is title1 and the content is content1 comment

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Db. post. find ({"comments": {"$ elemMatch": {"title": "comment1", "content": "content1 "}}});

Comments is an array document.