Shulou(Shulou.com)06/01 Report--

We talked about the CRUD operation of MongoDB earlier: the update operation of MongoDB is implemented through the update () function of the collection. This function takes two parameters: the document to be changed and what it looks like after the change. There are two ways to update a document: to update the document and to update parts of the document. Let's talk about these two situations:

1. Update the entire document

Suppose you now have the following document:

{"name": "zhangsan", "dad": "zhangyi", "mom": "lisi"}

If you think this is not good, you need to organize the information about father and mother into a new document: parents, plus an age field age. Then the new document is as follows:

{"name": "zhangsan", "age": 20, "parents": {dad: "zhangyi", "mom": "lisi"}}

If you want to replace the first document in the database with the second document above, the procedure for using update is as follows:

> var zhangsan = db.info.findOne ({"name": "zhangsan"}); > zhangsan {"_ id": ObjectId ("4ee37409c3fc1a9f80ad74ed"), "name": "zhangsan", "dad": "zhangyi", "mom": "lisi"} > zhangsan.parents= {"dad": zhangsan.dad, "mom": zhangsan.mom} {"dad": "zhangyi", "mom": "lisi"} > zhangsan {"_ id": ObjectId ("4ee37409c3fc1a9f80ad74ed"), "name": "zhangsan", "dad": "zhangyi", "mom": "lisi", "parents": {"dad": "zhangyi", "mom": "lisi"} > zhangsan.age=2020 > zhangsan {"_ id": ObjectId ("4ee37409c3fc1a9f80ad74ed"), "name": "zhangsan" "dad": "zhangyi", "mom": "lisi", "parents": {"dad": "zhangyi", "mom": "lisi"}, "age": 20} > delete zhangsan.dadtrue > zhangsan {"_ id": ObjectId ("4ee37409c3fc1a9f80ad74ed"), "name": "zhangsan", "mom": "lisi", "parents": {"dad": "zhangyi", "mom": "lisi"} "age": 20} > delete zhangsan.momtrue > zhangsan {"_ id": ObjectId ("4ee37409c3fc1a9f80ad74ed"), "name": "zhangsan", "parents": {"dad": "zhangyi", "mom": "lisi"}, "age": 20} > db.info.update ({"_ id": ObjectId ("4ee37409c3fc1a9f80ad74ed")}, zhangsan) > db.info.find (); {"_ id": ObjectId ("4ee37409c3fc1a9f80ad74ed"), "name": "zhangsan", "parents": {"dad": "zhangyi", "mom": "lisi"}, "age": 20} >

One thing to note about document updates in this way is to match documents that need to be replaced through _ id as much as possible. As for why, I think anyone who has used the database should be able to understand (similar to matching feature records with primary keys).

two。 Use the modifier section to modify part of the document

A) $set modifier

The $set modifier specifies a new value for a key, or creates a new one if it does not exist. We will add a wife key-value pair to the above zhangsan document (in the database).

> db.info.update ({"_ id": ObjectId ("4ee37409c3fc1a9f80ad74ed")}, {"$set": {"wife": "wangwu"}); > db.info.find (); {"_ id": ObjectId ("4ee37409c3fc1a9f80ad74ed"), "age": 20, "name": "zhangsan", "parents": {"dad": "zhangyi", "mom": "lisi"}, "wife": "wangwu"} >

Now that a year has passed and Zhang San is 21 years old, you can update the value of the age key with $set:

> db.info.update ({"_ id": ObjectId ("4ee37409c3fc1a9f80ad74ed")}, {"$set": {"age": 21}}); > db.info.find (); {"_ id": ObjectId ("4ee37409c3fc1a9f80ad74ed"), "age": 21, "name": "zhangsan", "parents": {"dad": "zhangyi", "mom": "lisi"}, "wife": "wangwu"} >

Of course, there are other modifiers that can be implemented in this case, and they are more appropriate, which we will continue to cover in a moment.

Zhangsan is divorced and has no wife. What are we going to do? We can undo the key-value pair wife with the $unset modifier. (PS: this example is not very appropriate. It's cruel.)

> db.info.update ({"_ id": ObjectId ("4ee37409c3fc1a9f80ad74ed")}, {"$unset": {"wife": 1}}); > db.info.find (); {"_ id": ObjectId ("4ee37409c3fc1a9f80ad74ed"), "age": 21, "name": "zhangsan", "parents": {"dad": "zhangyi", "mom": "lisi"}} >

B) $inc modifier

The $inc modifier increases and modifies the values of existing keys (for numeric types only). As we mentioned above, as zhangsan ages over time, you can use this modifier:

> db.info.update ({"_ id": ObjectId ("4ee37409c3fc1a9f80ad74ed")}, {"$inc": {"age": 1}}); > db.info.find (); {"_ id": ObjectId ("4ee37409c3fc1a9f80ad74ed"), "age": 22, "name": "zhangsan", "parents": {"dad": "zhangyi", "mom": "lisi"}} >

This modifier is ideal for situations such as voting, scoring, traffic statistics, and so on. Note, however, that this selector is only suitable for increasing and decreasing key-value pairs of numeric types. To reduce it, you only need to pass a negative value.

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