Use of MongoDB modifier 1

Why use modifiers?

Usually we only modify part of the document, it is cumbersome to update the entire document, usually through an atomic update modifier.

1. "$set" modifier

"$set" is used to specify a field that is created if it does not exist. This is very convenient for some updates or additions.

Such as:

Step1: As long as a data to the users database, through JavaScript to complete:

var logs={name: "Joe", Age:30,sex: "Female", Location: "Wisconsin"}

Logs

Run:

1 /*1*/2 {3     "name":"Joe",4     " Age":30.0,5     "Sex":"female",6     " Location":"Wisconsin"7}

Step2: Put into the users database

Db.users.insert (Logs)

Query Result:

Db.users.find ()

/*1*/{    "_id": ObjectId ("575a2acfbc9fb3f12145a004"),    "name":"Joe",    " Age":30.0,    "Sex":"female",    " Location":"Wisconsin"}

Step3: Join to insert a favorite book:

Db.users.update ({name: "Joe"},{"$set": {"Favorite book": "War and Peace"}})

Then query Db.users.find ()

/*1*/{    "_id": ObjectId ("575a2acfbc9fb3f12145a004"),    "name":"Joe",    " Age":30.0,    "Sex":"female",    " Location":"Wisconsin",    "Favorite Book":"War and Peace"}

From the results we can see that a favorite book field has been added to the data to achieve the results we want ^_^;

Step4: If Joe likes another book, continue to see how "$set" is going to be a big fan.

/*1*/{    "_id": ObjectId ("575a2acfbc9fb3f12145a004"),    "name":"Joe",    " Age":30.0,    "Sex":"female",    " Location":"Wisconsin",    "Favorite Book":"Forrest Gump"}

"$Set" can also modify the type of the key, for example, like a lot of books, you can put in the array.

As follows:

Db.users.update ({name: "Joe"},{"$set": {"Favorite book": ["Cat ' s Cradle", "Foundation Trilogy", "Ender ' Game"]})

/*1*/{    "_id": ObjectId ("575a2acfbc9fb3f12145a004"),    "name":"Joe",    " Age":30.0,    "Sex":"female",    " Location":"Wisconsin",    "Favorite Book" : [         "Cat ' s Cradle",         "Foundation Trilogy",         "Ender ' s Game"    ]}

You can also delete a field by using "$unset"

Db.users.update ({name: "Joe"},{"$unset": {"Favorite book": 1}})

/*1*/{    "_id": ObjectId ("575a2acfbc9fb3f12145a004"),    "name":"Joe",    " Age":30.0,    "Sex":"female",    " Location":"Wisconsin"}

This is the same as the beginning.

"$set" can also modify an inline document

Such as:

var log={title: "A Blog Post", Content: "...", Author:{name: "Joe", Email: "[email protected]"}
Log
Db.blog.posts.insert (log)
Db.blog.posts.findOne ()

/*1*/{    "_id": ObjectId ("575a313fbc9fb3f12145a008"),    "title":"A Blog Post",    "content":"...",    "author" : {        "name":"Joe",        "Email":"[email protected]"    }}

Db.blog.posts.update ({"Author.name": "Joe"},{"$set": {"Author.name": "Joe Mather"}})

/*1*/{    "_id": ObjectId ("575a313fbc9fb3f12145a008"),    "title":"A Blog Post",    "content":"...",    "author" : {        "name":"Joe Mather",        "Email":"[email protected]"    }}

Summary: The modifier that begins with the $ starts with the primary key to modify the corresponding content.

Use of MongoDB modifier 1