Python中使用MongoEngine

时间:2022-06-19
本文章向大家介绍Python中使用MongoEngine，主要内容包括其使用实例、应用技巧、基本知识点总结和需要注意事项，具有一定的参考价值，需要的朋友可以参考一下。

Python中使用MongoEngine1

pymongo来操作MongoDB数据库，但是直接把对于数据库的操作代码都写在脚本中，这会让应用的代码耦合性太强，而且不利于代码的优化管理

一般应用都是使用MVC框架来设计的，为了更好地维持MVC结构，需要把数据库操作部分作为model抽离出来，这就需要借助MongoEngine

MongoEngine是一个对象文档映射器（ODM），相当于一个基于SQL的对象关系映射器（ORM）

MongoEngine提供的抽象是基于类的，创建的所有模型都是类

安装

pip install mongoengine

使用时先声明一个继承自MongoEngine.Document的类

在类中声明一些属性，相当于创建一个用来保存数据的数据结构，即数据已类似数据结构的形式存入数据库中，通常把这样的一些类都存放在一个脚本中，作为应用的Model模块

from mongoengine import *
connect('test', host='localhost', port=27017)
import datetime
class Users(Document):
    name = StringField(required=True, max_length=200)
    age = IntField(required=True)

users = Users.objects.all() #返回所有的文档对象列表
for u in users:
    print("name:",u.name,",age:",u.age)

保存文档

from mongoengine import *
connect('test', host='localhost', port=27017)
import datetime
class Users(Document):
    name = StringField(required=True, max_length=200)
    age = IntField(required=True)
user1 = Users(
    name='zz',
    age= 11
)
user1.save()   
print(user1.name)
user1.name = 'zz11'
user1.save()       
print(user1.name)

查询10=<年龄<30的，按姓名排列

from mongoengine import *
connect('test', host='localhost', port=27017)
import datetime
class Users(Document):
    name = StringField(required=True, max_length=200)
    age = IntField(required=True)
user_search = Users.objects(age__gte=10, age__lt=33).order_by('name')
for u in user_search:
    print("name:",u.name,",age:",u.age)

查询10=<年龄<30的，按姓名倒序

from mongoengine import *
connect('test', host='localhost', port=27017)
import datetime
class Users(Document):
    name = StringField(required=True, max_length=200)
    age = IntField(required=True)
user_search = Users.objects(age__gte=10, age__lt=33).order_by('-name')
for u in user_search:
    print("name:",u.name,",age:",u.age)

查询name=zz11

from mongoengine import *
connect('test', host='localhost', port=27017)
import datetime
class Users(Document):
    name = StringField(required=True, max_length=200)
    age = IntField(required=True)

tmp = Users.objects(name="zz11")
for u in tmp:
    print("name:",u.name,",age:",u.age)

修改name=zz11的age加1

from mongoengine import *
connect('test', host='localhost', port=27017)
import datetime
class Users(Document):
    name = StringField(required=True, max_length=200)
    age = IntField(required=True)
tmp = Users.objects(name="zz11").update(inc__age=1)
tmp = Users.objects(name="zz11")
for u in tmp:
    print("name:",u.name,",age:",u.age)

修改name=zz11的age设为55

from mongoengine import *
connect('test', host='localhost', port=27017)
import datetime
class Users(Document):
    name = StringField(required=True, max_length=200)
    age = IntField(required=True)

tmp = Users.objects(name="zz11").update(set__age=55)
tmp = Users.objects(name="zz11")
for u in tmp:
    print("name:",u.name,",age:",u.age)

Python中使用MongoEngine2

mongoengine基本用法实例：

from mongoengine import *
from datetime import datetime

#连接数据库:test
# connect('test')    # 连接本地test数据库
connect('test', host='127.0.0.1', port=27017, username='test', password='test')

# Defining our documents
# 定义文档user,post,对应集合user,post
class User(Document):
    # required为True则必须赋予初始值
    email = StringField(required=True)
    first_name = StringField(max_length=50)
    last_name = StringField(max_length=50)
    date = DateTimeField(default=datetime.now(), required=True)

# Embedded documents,it doesn’t have its own collection in the database
class Comment(EmbeddedDocument):
    content = StringField()
    name = StringField(max_length=120)

class Post(Document):
    title = StringField(max_length=120, required=True)
    # ReferenceField相当于foreign key
    author = ReferenceField(User)
    tags = ListField(StringField(max_length=30))
    comments = ListField(EmbeddedDocumentField(Comment))
    # 允许继承
    meta = {'allow_inheritance': True}

class TextPost(Post):
    content = StringField()

class ImagePost(Post):
    image_path = StringField()

class LinkPost(Post):
    link_url = StringField()

# Dynamic document schemas:DynamicDocument documents work in the same way as Document but any data / attributes set to them will also be saved
class Page(DynamicDocument):
    title = StringField(max_length=200, required=True)
    date_modified = DateTimeField(default=datetime.now())

添加数据

john = User(email='john@example.com', first_name='John', last_name='Tao').save()
ross = User(email='ross@example.com')
ross.first_name = 'Ross'
ross.last_name = 'Lawley'
ross.save()

comment1 = Comment(content='Good work!',name = 'LindenTao')
comment2 = Comment(content='Nice article!')
post0 = Post(title = 'post0',tags = ['post_0_tag'])
post0.comments = [comment1,comment2]
post0.save()

post1 = TextPost(title='Fun with MongoEngine', author=john)
post1.content = 'Took a look at MongoEngine today, looks pretty cool.'
post1.tags = ['mongodb', 'mongoengine']
post1.save()

post2 = LinkPost(title='MongoEngine Documentation', author=ross)
post2.link_url = 'http://docs.mongoengine.com/'
post2.tags = ['mongoengine']
post2.save()

# Create a new page and add tags
page = Page(title='Using MongoEngine')
page.tags = ['mongodb', 'mongoengine']
page.save()

创建了三个集合:user,post,page

查看数据

# 查看数据
for post in Post.objects:
    print post.title
    print '=' * len(post.title)

    if isinstance(post, TextPost):
        print post.content

    if isinstance(post, LinkPost):
        print 'Link:', post.link_url

# 通过引用字段直接获取引用文档对象    
for post in TextPost.objects:
    print post.content
    print post.author.email  
au = TextPost.objects.all().first().author
print au.email

# 通过标签查询    
for post in Post.objects(tags='mongodb'):
    print post.title   
num_posts = Post.objects(tags='mongodb').count()
print 'Found %d posts with tag "mongodb"' % num_posts

# 多条件查询(导入Q类) 
User.objects((Q(country='uk') & Q(age__gte=18)) | Q(age__gte=20))   

# 更新文档
ross = User.objects(first_name = 'Ross')
ross.update(date = datetime.now())
User.objects(first_name='John').update(set__email='123456@qq.com')
//对 lorem 添加商品图片信息
lorempic = GoodsPic(name='l2.jpg', path='/static/images/l2.jpg')
lorem = Goods.objects(id='575d38e336dc6a55d048f35f')
lorem.update_one(push__pic=lorempic)
# 删除文档
ross.delete()

备注

ORM全称“Object Relational Mapping”，即对象-关系映射，就是把关系数据库的一行映射为一个对象，也就是一个类对应一个表，这样，写代码更简单，不用直接操作SQL语句。

Python中使用MongoEngine3

最近重新拾起Django,但是Django并不支持mongodb,但是有一个模块mongoengine可以实现Django Model类似的封装.但是mongoengine的中文文档几乎没有,有的也是简短的几句介绍和使用.下面我就分享一下我在使用过程中所记录下的一些笔记,可能有点乱.大家可以参考一下.

安装mongoengine

easy_install pymongo # 依赖库
easy_install mongoengine

基本使用

from mongoengine import *
from datetime import datetime
# 连接数据库
connect('blog')   # 连接本地blog数据库
# 如需验证和指定主机名
# connect('blog', host='192.168.3.1', username='root', password='1234')

# 定义分类文档
class Categories(Document):
    ' 继承Document类,为普通文档 '
    name = StringField(max_length=30, required=True)
    artnum = IntField(default=0, required=True)
    date = DateTimeField(default=datetime.now(), required=True)

和Django的model使用很类似,所以也不解释什么.

插入

cate = Categories(name="Linux")   # 如果required为True则必须赋予初始值,如果有default,赋予初始值则使用默认值
cate.save() # 保存到数据库

查询和更新

文档类有一个 objects 属性.我们使用它来查询数据库.

# 返回集合里的所有文档对象的列表
cate = Categories.objects.all()

# 返回所有符合查询条件的结果的文档对象列表
cate = Categories.objects(name="Python")
# 更新查询到的文档:
cate.name = "LinuxZen"
cate.update()
查询数组 默认查询数组"="代表的意思是in:
class Posts(Document):
    artid = IntField(required=True)
    title = StringField(max_length=100, required=True)
    content = StringField(required=True)
    author = ReferenceField(User)
    tags = ListField(StringField(max_length=20, required=True), required=True)
    categories = ReferenceField(Categories), required=True)
    comments = IntField(default=0, required=True)

# 将会返回所有tags包含coding的文档
Posts.objects(tags='coding')

ReferenceField 引用字段:

通过引用字段可以通过文档直接获取引用字段引用的那个文档:

class Categories(Document):
    name = StringField(max_length=30, required=True)
    artnum = IntField(default=0, required=True)
    date = DateTimeField(default=datetime.now(), required=True)

class Posts(Document):

    title = StringField(max_length=100, required=True)
    content = StringField(required=True)
    tags = ListField(StringField(max_length=20, required=True), required=True)
    categories = ReferenceField(Categories)

插入引用字段

cate =Categories(name="Linux")
cate.save()
post = Posts(title="Linuxzen.com", content="Linuxzen.com",tags=["Linux","web"], categories=cate)
post.save()

通过引用字段直接获取引用文档对象

一般文档查询会返回一个列表(尽管只有一个结果),我们想要获得一个文档对象可以使用索引获取第一个文档对象,但是mongoengine建议使用first()来获取第一个:

>>> cate = Posts.objects.all().first().categories
>>> cate

>>> cate.name
u'Linux'

查询包含Linux分类的文章

>>> cate = Categories.objects(name="Linux").first()
>>> Posts.objects(categories=cate)

EmbeddedDocument 嵌入文档

继承EmbeddedDocument的文档类就是嵌入文档,嵌入文档用于嵌入其他文档的EmbeddedDocumentField 字段,比如上面例子的tags字段如果改成嵌入文档的话可以将Posts文档类改成如下方式:

class Posts(Document):

    title = StringField(max_length=100, required=True)
    content = StringField(required=True)
    tags = ListField(EmbeddedDocumentField('Tags')required=True)
    categories = ReferenceField(Categories)

还需要添加一个Tags嵌入文档类:

class Tags(EmbeddedDocument):
name = StringField()
date = DateTimeField(default=datetime.now())

我们像如下方式插入Posts文档中的Tags

>>> tag = Tags(name="Linuxzen")
>>> post = Posts(title="Linuxzen.com", content="Linuxzen.com", tags=[tag], categories=cate)
>>> tag = Tags(name="mysite")
>>> post.tags.append(tag)
>>> post.save()
>>> tags = post.tags
>>> for tag in tags:
print tag.name

Linuxzen
mysite

时间段查询

    start = datetime(int(year), int(month), 1)
    if int(month) + 1 > 12:
        emonth = 1
        eyear = int(year) + 1
    else:
        emonth = int(month) + 1
        eyear = int(year)
    end = datetime(eyear, emonth, 1)
    articles = Posts.objects(date__gte=start, date__lt=end).order_by('-date')

分片

slice用于分片

# comments - skip 5, limit 10
Page.objects.fields(slice__comments=[5, 10])

# 也可以使用索引值分片

# limit 5
users = User.objects[:5]

# skip 5
users = User.objects[5:]

# skip 10, limit 15
users = User.objects[10:15]

使用原始语句查询

如果想使用原始的pymongo查询方式可以使用raw操作符 Page.objects(raw={‘tags’:’coding’}) 使用inc和inc和inc和set操作符

# 更新嵌入文档comments字段by的值为joe的文档字段votes增加1
Page.objects(comments_by="joe").update(inc__votes=1)

# 更新嵌入文档comments字段by的值为joe的文档字段votes设置为1
Page.objects(comments_by="joe").update(set__votes=1)

其他技巧

#查询结果转换成字典
users_dict = User.objects().to_mongo()

# 排序,按日期排列
user = User.objects.order_by("date")

# 按日期倒序

user = User.objects.order_by("-date")

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