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MongoDB is a document-oriented database, not a relational database. It extends many useful functions of relational database, such as auxiliary query, range query and sorting.

It replaces the original concept of lines with a more flexible document model. It has no schema: the keys of the document are not defined in advance and are not fixed.

MongoDB stores the data as a document, and the data structure consists of key-value (key= > value) pairs. MongoDB documents are similar to JSON objects. Field values can contain other documents, arrays, and document arrays.

Some common features of relational databases, such as join and complex multiline transactions, are not available in MongoDB.

MongoDB is scalable, and its document-oriented data model enables it to automatically split data among multiple servers.

MongoDB has superior performance. It leaves memory management to the operating system; it uses the query optimizer to remember the most efficient way to execute queries; and it uses pre-allocated data files (using space) in exchange for stable performance.

The management idea of MongoDB is to let the server be configured automatically as much as possible to simplify the management of the database. For example, if the primary server dies, it automatically switches to the backup server and promotes the backup server to an active server.

Introduction to NoSQL

NoSQL (NoSQL = Not Only SQL), which means "not just SQL". But in fact, many NoSQL databases have given up support for the SQL language.

MongoDB installation start and stop

For installation methods, please see:

Install MongoDB Community EditionHow to Install MongoDB on Ubuntu 16.04-DigitalOceanHow to Install and Configure MongoDB on Ubuntu 16.04

Enable mongod:

Sudo service mongod start

Enter mongo shell:

Mongo

List the databases:

Show dbs

Displays the current database object:

Db

The default is test.

Switch the database:

Use

Stop mongod:

Sudo service mongod stop

Or use the following more secure way to stop MongoDB:

# switch to admin database (allow yourself to have administrator privileges) use admindb.shutdownServer ()

The newly installed mongodb does not enable user rights authentication; therefore, no authentication is required to connect.

The basic concept of MongoDB

The basic concepts in mongodb are documents, collections, and databases.

SQL terminology / concept MongoDB terminology / concept explanation / description databasedatabase database tablecollection database table / collection rowdocument data record row / document columnfield data field / domain indexindex index table joins table join, MongoDB does not support primary keyprimary key primary key, MongoDB automatically sets the _ id field to the primary key document

A document is similar to a row in a relational database. Multiple keys and their associated values are placed together in order to form a document. In JS, documents are represented as objects.

Each document has a special key _ id, which is unique in the collection in which the document resides.

Several important concepts:

The key / value pairs in the document are ordered.

The key of the document is a string. In general, keys can use UTF-8 characters.

The key cannot have\ 0 empty characters. It is used to indicate the end of the key. . And $can only be used in a specific environment. Keys starting with _ are reserved.

MongoDB is not only type-sensitive, but also case-sensitive. Here are two different sets of documents:

{"foo": 3} {"foo": "3"} {"foo": 3} {"Foo": 3}

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MongoDB documents cannot have duplicate keys. Set

Collections can be thought of as tables without schemas.

Subset:

One of the conventions for organizing collections is to use. A subset of namespace partitions separated by characters. For example:

Blog.post and blog.authors, this is just to make the organizational structure better, which means that the collection of blog (which doesn't need to exist at all) and its subsets have nothing to do with it.

Database

A MongoDB instance can host multiple databases. Different databases are stored in different files

Keep in mind that database names will eventually become files in the file system, so database names must follow some conventions.

Reserved special database:

Admin: from a permissions perspective, this is a root database. Local: this database is never replicated and can be used to store any collection limited to the local server. Config: however, when Mongo is used for sharding settings, the config database is used internally to store information about sharding.

Namespace: put the name of the database in front of the collection name to get the fully qualified name of the collection.

Data type

MongoDB's documentation is similar to JSON and conceptually similar to objects in JavaScript. MongoDB adds some other data types while retaining the basic key / value pair features of JSON. These types represent slightly different representations in different programming languages.

Null:

Boolean:

32-bit integer:

64-bit integer:

64-bit floating point number:

String

Symbol

Object id:ObjectId (). (the document must have a "_ id" key; the value of this key can be of any type, and the default is the ObjectId object. )

Date: new Date ()

Regular expressions: using JavaScript's regular expression syntax

Code: the document can also contain JavaScript code

{"x": function () {/ * * /}}

Binary data:

Maximum value

Minimum value

Undefined

Array: a collection or list of values can be represented as an array

{"x": ["a", "b", "c"]} embedded document:

A document can contain other documents, or it can be embedded as a value in the parent document {"x": {"foo": "bar"}} database management

Default data directory / data/db and use port 27017. It also starts a very basic http server, listening on ports with a number 1000 higher than the primary port number, such as port 28017.

MongoDB Shell

MongoDB comes with a JavaScript shell that can interact with MongoDB instances from the command line. It is also a complete JS interpreter that can run any JS program.

When turned on, shell connects to the test database of the MongoDB server and assigns the database connection to the global variable db. This variable is the main entry point for accessing MongoDB through shell.

Shell also provides some syntax sugar, such as selecting the usr dbName of the database, and the value of the db variable will also change after performing this operation.

# run mongo to start shellmongo# to list the database show dbs# to switch the database. If the database does not exist, create the database use imooc# delete the database db.dropDatabase () add, delete, change, check and insert the document

Using the insert method on the target set, insert a document:

Db.foo.insert ({"bar": "baz"})

This operation automatically adds a "_ id" key (if it doesn't already exist) and saves it to the database.

Bulk insert:

Batch inserts can pass an array of documents to the database.

When inserting data: the database will only verify that it contains the "_ id" key, and then simply store the document in the database as is.

MongoDB does not execute code when it is inserted, so there is no possibility of injection.

Delete document

Delete all documents in the users collection, but not the collection itself:

Db.users.remove ()

The remove function can accept a query document as an optional argument. This way, only documents that meet the criteria can be deleted.

Example: all "optout" is true will be deleted:

Db.mailing.list.remove ({"opt-out": true})

Delete the collection directly: db.drop_collection ("bar")

Update document

Use the update method. This method consists of two parameters, one is to query the document, which is used to find the document to update, and the other is the modifier document, which describes what changes have been made to the found document.

The update operation is atomic: if two updates occur at the same time, the first one that arrives at the server is executed first, followed by another one.

Update modifier: a special key that specifies complex update operations.

"$set" modifier

The $set modifier is used to specify the value of a key. If the key does not exist, create it.

Example: add a favorite book to a user information

Db.users.update ({"_ id": ObjectId ("4fksdftudkf4964trub")}, / / query document {"$set": {"favorite book": "war and peace"}} / / modifier documentation)

The corresponding key can be completely deleted using "$unset".

"$inc" modifier

"$inc" modifier: used to increase an existing value and create a key if it does not exist.

It can only be used for integer, long integer live floating point numbers.

Db.games.update ({"game": "pinball", "user": "joe"}, / / query document {"$inc": {"score": 50}}) / / modifier documentation

Example above: players who meet the criteria will add 50 points, and if the score key does not exist, it will be created first. The increment here is 50.

"$push" modifier

For arrays. The "$push" modifier adds an element to the end of an existing array, or creates a new array if the key does not exist.

Note: this means that the value of a key in the collection is an array, and now you want to add elements to this array.

For example, the blog.post collection is as follows:

{id: ObjectId ("4dkfs53rt9rufhvjr0fv"), title: "A blog post", content: "...", comments: [{name: "joe", email: "joe@gmail.com", content: "nice post"}]}

When we want to add an element to the comments array, we can use $push.

Query document

Use find or findOne functions and query documents to query the database.

To query a simple type, just specify the value you want to find. Example, find all documents with a value of 27 for "age":

Db.users.find ({"age": 27})

Query criteria:

The correlation operator describes that $lt=$ne is not equal to $in to query multiple values of a key $nin returns documents that do not match all conditions in the array $or is used to complete any given value of multiple key values $not is a meta statement and can be used on any other condition

Query users aged 18-30:

Db.users.find ({"age": {"$gte": 18, "$lte": 30}})

Use $in to do an OR query on a single key

Db.raffle.find ({"ticket_no": {"$in": [725542390]}})

You can use $or to do OR queries on multiple keys. For example, find a document whose ticket_no is 725 or winner is true:

Db.raffle.find ({"$or": [{"ticket_no": 725}, {"winner", true}]}) query array

For example, an array is a list of fruits

Db.food.insert ({"fruit": ["apple", "banana", "peach"]})

The following query matches the document:

Db.food.find ({"fruit", "banana"})

$all: matches the array through multiple elements.

Find the document with both apple and banana:

Db.food.find ({fruit: {$all: ["apple", "banana"]}})

$size is used to query an array of specified length.

Db.food.find ({fruit: {$size: 3}}) query embedded documents

It would be better to allow queries usually only against specific key values of embedded documents, so that even if the data schema changes, it won't be too much of a problem.

We can use dot notation to query embedded keys:

Db.people.find ({"name.first": "Joe", "name.last": "Schome"}) "$where" query

The "$where" clause can execute any JavaScipt as part of the query. By its supplement, the query can do anything.

The most typical application is to compare whether the values of two keys in a document are equal.

Db.foo.find ({"$where": "function () {return this.x + this.y = = 10;}"})

Note: the "$where" query is much slower than other regular queries.

Vernier

The database uses cursors to return the execution results of find. The object returned by find is a cursor.

Methods of cursors:

Next (): get the next result hasNext (): check for the existence of subsequent results limit (): limit the number of results skip (): ignore a certain number of results sort (): sort the results

Almost all the method return values of cursors are also cursors, so that you can form a method chain.

Manage MongoDB to start MongoDB from the command line

Simply start the server by executing mongod directly. There are many configurable startup options for this command:

Option description-- help views all options-- dbpath specifies the data directory. The default value is / data/db--port, which specifies the port number that the server listens to-- fork runs MongoDB as a daemon, and the creation server process-- logpath specifies the log output path, rather than output to the command line-- config specifies the configuration file. # in the configuration file is an annotation symbol; the grammatical form is the "option-value" analogy.

Each mongod process requires a separate data directory. When mongod starts, a mongod.lock file is created in the data directory, which is used to prevent other mongod processes from using the data directory. And assign them different port numbers.

Stop MongoDB

Here is only one safe way to stop the database: use the shutdown command, {"shutdown": 1}, which is an administrative command to use under the admin database. MongoDB shell provides helper functions to simplify this process:

> use adminswitched to db admin > db.shutdownServer (); server should be down... Learning materials

Authoritative Guide to MongoDB

MongoDB tutorial-Rookie tutorial

Official manual: The MongoDB Manual

MongoDB Chinese Community

MongoDB Chinese website

Mongodb Best practices-Maizi College

MongoDB basic course-Mu course net course

Graphic tool: Robo 3T-formerly Robomongo-native MongoDB management tool (Admin UI)

From my brief book: faner-brief book

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