MongoDB基礎教程

MongoDB是數據庫,是應用程序中負責存儲和檢索信息的部分。

MongoDB是一個NoSQL數據庫。在下面NoSQL我們將所有不使用SQL語言的數據庫都放在查詢數據中。

MongoDB的主要特徵

MongoDB是一個非常友好的JavaScript數據庫。它公開了一個JavaScript API,可用於創建數據庫和對象集合(稱為單據)。

它是無模式,這意味著您無需在存儲數據之前為數據預定義結構。

在MongoDB中,您可以存儲任何對象,而不必擔心組成該對象的特定字段以及如何存儲它們。您告訴MongoDB存儲該對象。

數據以類似於JSON的格式存儲,但經過增強後可以存儲的不僅僅是基本數據類型。

安裝

讓我們繼續安裝MongoDB。您可以使用提供訪問MongoDB實例的眾多雲提供商之一,但是為了學習起見,我們將自行安裝它。

我使用的是Mac,因此本教程中的安裝說明涉及該操作系統。

打開終端並運行:

brew tap mongodb/brew
brew install mongodb-community

而已。

假設您知道如何使用終端和如何安裝自製軟件

安裝過程告訴我們:

To have launchd start mongodb now and restart at login:
  brew services start mongodb-community
Or, if you don't want/need a background service you can just run:
  mongod --config /usr/local/etc/mongod.conf

You can choose to either launch MongoDB once and have it running forever as a background service in your computer (the thing I prefer), or you can run it just when you need it, by running the latter command.

The default configuration for MongoDB is this:

systemLog:
  destination: file
  path: /usr/local/var/log/mongodb/mongo.log
  logAppend: true
storage:
  dbPath: /usr/local/var/mongodb
net:
  bindIp: 127.0.0.1

Logs are stored in /usr/local/var/log/mongodb/mongo.log and the database is stored in /usr/local/var/mongodb.

By default there is no access control, anyone can read and write to the database.

The Mongo Shell

The best way to experiment with MongoDB and starting to interact with it is by running the mongo program, which starts the MongoDB shell.

You can now enter any command that Mongo understands.

Create a database

When you start, Mongo creates a database called test. Run db in the shell to tell you the name of the active database

To change the database, just write use newname and the newname database will be instantly created and the shell switches to using that.

Use show databases to list the available databases:

As you can see, the something database is not listed, just because there is no collection yet in it. Let’s create one.

Collections

In MongoDB, a collection is the equivalent of a SQL database table.

You create a collection on the current database by using the db.createCollection() command. The first argument is the database name, and you can pass an options object as a second parameter.

Once you do so, show databases will list the new database, and show collections will list the collection.

You can also create a new collection by using it as a property of the db object, and calling insert() to add an object to the collection:

db.dogs.insert({ name: 'Roger' })

Listing objects in a collection

To show the objects added to a collection, use the find() method:

As you can see there is an additional _id property for the record we added. That’s automatically generated for us by MongoDB.

Now, add more dogs:

db.dogs.insert({ name: 'Buck' })
db.dogs.insert({ name: 'Togo' })
db.dogs.insert({ name: 'Balto' })

Calling db.dogs.find() will give us all the entries, while we can pass a parameter to filter and retrieve a specific entry, for example with db.dogs.find({name: 'Roger'}):

The find() method returns a cursor you need to iterate on.

There is another method which is handy when you know you’ll only get one record, which is findOne(), and it’s used in the same way. If multiple records match a query, it will just return the first one.

Updating records

To update a record you can use the update() method on a collection:

Removing records

You can remove a record calling the remove() method on a collection, passing an object to help identify it:

To remove all the entries from a collection, pass an empty object:

db.dogs.remove({})

More database tutorials: