Summary of commonly used statements in MongoDB

This article brings you a summary of commonly used statements in MongoDB. It has certain reference value. Friends in need can refer to it. I hope it will be helpful to you.

If you feel that Mongodb statements are not easy to understand, you can compare them with SQL statements. It will be much easier to learn.

1. Query (find)

Query all results

select * from article
db.article.find()

Specify which keys to return

select title, author from article
db.article.find({}, {"title": 1, "author": 1})

where conditions

select * from article where title = "mongodb"
db.article.find({"title": "mongodb"})

and condition

select * from article where title = "mongodb" and author = "god"
db.article.find({"title": "mongodb", "author": "god"})

or condition

select * from article where title = "mongodb" or author = "god"
db.article.find({"$or": [{"title": "mongodb"}, {"author": "god"}]})

Comparison condition

select * from article where read >= 100;
db.article.find({"read": {"$gt": 100}})

> $gt(>)、$gte(>=)、$lt(d465e952edbc4325ec7a8892c05fa947= 100 and read 4dff936d362ade4fb470a7957746f016 100
db.article.update({"read": {"$gt": 100}}, {"$set": { "title": "mongodb"}})

save()

db.article.save({_id: 123, title: "mongodb"})

Execute the above statement, if there is already a document with _id 123 in the collection, update the corresponding field; otherwise insert.

Note: If the update object does not exist _id, the system will automatically generate it and insert it as a new document.

Update Operators

MongoDB provides some powerful update operators.

Update specific fields ($set):

update game set count = 10000 where _id = 123
db.game.update({"_id": 123}, { "$set": {"count": 10000}})

Delete specific fields ($unset):

Note: The value of the field specified by $unset only needs to be any legal value. Can.
Increment or decrement ($inc)

 db.game.update({"_id": 123}, { "$inc": {"count": 10}}) // 每次count都加10

> Note: The field corresponding to $inc must be a number, and the incrementing or decrementing value must also be a number.

Array append ($push):

 db.game.update({"_id": 123}, { "$push": {"score": 123}})

You can also append multiple elements at one time:

 db.game.update({"_id": 123}, {"$push": {"score": [12,123]}})

Note: The appended field must be an array. If the array field does not exist, it is automatically added and then appended.

Append multiple elements at one time ($pushAll):

 db.game.update({"_id": 123}, {"$pushAll": {"score": [12,123]}})

Append non-repeating elements ($addToSet):

$addToSet is similar to the set Set, only when this Increase only if the value is not within the element:

 db.game.update({"_id": 123}, {"$addToSet": {"score": 123}})

Delete element ($pop):

db.game.update({"_id": 123}, {"$pop": {"score": 1}})  // 删除最后一个元素
db.game.update({"_id": 123}, {"$pop": {"score": -1}})  // 删除第一个元素

Note: $pop can only delete one element in the array at a time, 1 means delete The last one, -1 means delete the first one.

Delete specific elements ($pull):

db.game.update({"_id": 123}, {"$pull": {"score": 123}})

The above statement means to delete the elements whose value is equal to 123 in the array score.

Delete multiple specific elements ($pullAll):

db.game.update({"_id": 123}, {"$pullAll": {score: [123,12]}})

The above statement means to delete the elements whose value is equal to 123 or 12 in the array.
Update the value of the nested array:
Use the array subscript (starting from 0):

{
    address: [{place: "nanji", tel: 123}, {place: "dongbei", tel: 321}]
}

 db.game.update({"_id": 123}, {"$set": {"address.0.tel": 213}})

If you don’t know which item of the array to update, we can use the $ operator ( $ represents itself, that is, the item itself in the array found according to the query conditions, and only the first array item found will be used):

 db.game.update({"address.place": "nanji"}, {"$set": {"address.$.tel": 123}})

In the above statement, $ is the query The query result of the condition {"address.place": "nanji"} is {place: "nanji", tel: 123}, so {"address.$.tel": 123} is also {"address.{place : "nanji", tel: 123}.tel": 123}

4. Delete (remove)

Delete all documents:

delete from article
db.article.remove()

Delete the specified document:

 delete from article where title = "mongodb"
 db.article.remove({title: "mongodb"})

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