MongoDB基础教程

MongoDB是数据库,是应用程序中负责存储和检索信息的部分。

MongoDB是一个NoSQL数据库。在下面NoSQL我们将所有不使用SQL语言的数据库都放在查询数据中。

MongoDB的主要特征

MongoDB是一个非常友好的JavaScript数据库。它公开了一个JavaScript API,可用于创建数据库和对象集合(称为单据)。

它是无模式,这意味着您无需在存储数据之前为数据预定义结构。

在MongoDB中,您可以存储任何对象,而不必担心组成该对象的特定字段以及如何存储它们。您告诉MongoDB存储该对象。

数据以类似于JSON的格式存储,但经过增强后可以存储的不仅仅是基本数据类型。

安装

让我们继续安装MongoDB。您可以使用提供访问MongoDB实例的众多云提供商之一,但是为了学习起见,我们将自行安装它。

我使用的是Mac,因此本教程中的安装说明涉及该操作系统。

打开终端并运行:

brew tap mongodb/brew
brew install mongodb-community

而已。

假设您知道如何使用终端和如何安装自制软件

安装过程告诉我们:

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: