MongoDB learning notes

01 - start MongoDB

// Open service
sudo service mongodb start
// Start MongoDB
mongo

02 - database operation command

// View the database in use in the current period
db
// View all databases
show dbs
// Connect or create myTest database
use myTest
// Destroy myTest database
use myTest
db.dropDatabase()

03 - creation and deletion of collections

// Create the users collection in the mytest database
use myTest
db.createCollection("users")
// View collections in the myTest database
show collections
// Delete users collection
db.users.drop()

04 - insert data into set

If there is no corresponding set in the database, the corresponding set will be automatically created when inserting the set.

// Inserts a document into the users collection
db.users.insert([{"name":"LiSi"},{"name":"WangWu"}])
// Define the data before inserting it
LiSi=({"name":"lisi","email":"888qq.com"})
db.users.insert(LiSi)

05 - save or modify data in the set

// Save data to the users collection, or modify an existing document
db.users.save([{"name":"LiSi"},{"name":"WangWu"}])

06 - update data in set

// Change the name in the document content with the name lisi in the users collection to "wangwu"
db.users.update({"name":"lisi"},{$set:{"name":"wangwu"}},{multi:true})

The content in the first brace is the query criteria, and the content in the second brace indicates the data and content to be updated.
By default, update updates only one document. If you want to update all data, you need to add "{multi: true}"

07 query data in collection

// Query all documents in the users collection
db.users.find()
// Format and display the queried data
db.users.find().pretty()
// Find the document with name lgl
db.users.find({"name":"lgl"}).pretty()
// Find lgl with name and mailbox“ 123@qq.com "Document for"
db.users.find({"name":"lgl","email":"123@qq.com"})
// Find lgl with name or mailbox“ 666@qq.com "Document for"
db.users.find({
	$or:[
	{"name":"lgl"},
	{"email":"666@qq.com"}
	]
}).pretty()

08 conditional operator and its application

// Find users older than 18 and younger than 25 in the users collection
// And the name is "666" or the email is“ 123@qq.com "Document for"
db.users.find({
	"ages": {$gt:18,$lt:25},
    $or: [
		{"name": "666"},
		{"email": "123@qq.com"}
	]
}).pretty()

gt: greater than greater than
lt: less than
gte: greater than equal
lte: less than equal

09 fuzzy query

// Find documents whose mailbox starts with '123' in the users collection
db.users.find({"email":/^123/}).pretty()
// Find documents with names ending in 'l' in the users collection
db.users.find({"name":/l$/}).pretty()

Application of 10 type conditional operator

Syntax: $type: [key]

The optional key values are as follows:

1: Double (Double)
2: String (String)
3: Object
4: Array
5: Binary data
7: Object ID(Object id)
8: Boolean type
9: Date
10: Empty (Null)
11: Regular expression
13: JS code (Javascript)
14: Symbol
15: JS code with scope (JavaScript with scope)
16: 32-bit integer
17: Timestamp
18: 64 bit integer
-1: Min key
127: max key

// Find a document with name type "string"
db.myTest.find({"name":{$type:2}})
// The above code is equivalent to:
db.myTest.find({"name":{$type:"string"}})

11 use of limit() and skip()

limit(n): limit the number of query output results to no more than n!

db.users.find().limit(3)

skip(m): skip the first m document data during output

// Skip the first three document data
db.users.find().skip(3)
// Skip the first three document data and limit the output document entries to no more than 3
db.users.find().limit(3).skip(3)

12 - sorting of output data

// Sort by name in ascending order
db.users.find().sort({"name":1})
// In sort: '1' indicates ascending order and '- 1' indicates descending order.

13 - create index

// Index Names
db.users.ensureIndex({"name":1})
// '1' indicates ascending order and '- 1' indicates descending order.

14 aggregate()

Syntax:

db.COLLECTION_NAME.aggregate([
	{$match:{x:1}},
	{$limit:NUM},
	{$skip:NUM},
	{$group:{_id:$age}},
	{$sort:{"doc_name":1}},
	{$limit:NUM},
	{$skip:NUM},
	{$match:{x:1}}
])

explain:

$match: query, the same as find;
$limit: limit the number of displayed results;
$skip: ignore the result quantity;
$sort: sort;
$group: combine the results according to the given expression (grouping and merging).

give an example:

// Count the number of documents with the same name in the users collection, and sort the results in ascending order
db.users.aggregate([
	{$group:{_id:"$name", user:{$sum:1}}},
	{$sort:{_id:1}}
])
// $name means to get the value of name.

15 - atomic operation

Atomic operation is either successful or failed. The execution succeeds in completing a given task, and the execution fails to restore the state before execution.

Common atomic operation commands:

01,$set

Used to specify a key and update the key value. If the key does not exist, it is created.

{ $set : { field : value } }

02,$unset

Used to delete a key.

{ $unset : { field : 1} }

03,$inc

$inc can increase or decrease a key whose value is numeric (only numbers that meet the requirements).

{ $inc : { field : value } }

04,$push

Add value to the field. The field must be an array type. If the field does not exist, an array type will be added.

{ $push : { field : value } }

05,$pushAll

The same as $push, but multiple values can be appended to an array field at one time.

{ $pushAll : { field : value_array } }

06,$pull

Deletes a value equal to value from the array field.

{ $pull : { field : _value } }

07,$addToSet

Add a value to the array, and only if the value is not in the array.

08,$pop

Deletes the first or last element of the array.

{ $pop : { field : 1 } }

10,$rename

Modify field name:

{ $rename : { old_field_name : new_field_name } }

11,$bit

Bit operation, integer type

{$bit : { field : {and : 5}}}

Posted by predator on Tue, 23 Nov 2021 12:40:29 -0800

Programmer Group

MongoDB learning notes