我已经开始编写一个供 mongodb 使用的简单模块。我是 python 的新手，我写的代码有问题:
import pymongo
class mongoDB():
conn = object
def __init__(self):
global conn
self.conn = pymongo.Connection("localhost",27017)
def CreateCollection(self,name =""):
self.dbCollection = conn.name
return self.dbCollection
if __name__ == '__main__':
database = mongoDB
collection = database.CreateCollection("Hello")
首先，如果您能发现并纠正我，我认为我的代码可能没有什么问题。我也一直收到这个错误:
collection = database.CreateCollection("Hello")
TypeError: unbound method CreateCollection() must be called with mongoDB
instance as first argument (got str instance instead)
我希望能够在类的构造函数中创建连接，然后有一个创建集合并返回它的方法，以及另一个插入删除和更新实体的方法
请您参考如下方法:
所以，在语法方面你有很多问题。看起来您正在以不同的方式混合使用几个教程。所以，首先我会解释你的代码发生了什么，并解释为什么你会看到你所看到的:
import pymongo
class mongoDB(): # you don't need ()'s here - only if you are inheriting classes
# you could inherit from object here, which is a good practice
# by doing class mongoDb(object):, otherwise you can just take
# them out
conn = object # here, you're defining a class member - global for all instances
# generally, you don't instantiate an object pointer like this,
# you would set it to None instead. It won't fail doing this,
# but it's not "right"
def __init__(self):
# the __init__ method is the constructor method - this will
# allow you to initialize a particular instance of your class, represented
# by the self argument. This method is called when you call the class, i.e.
# inst = mongoDb()
# in this case, the conn variable is not a global. Globals are defined
# at the root module level - so in this example, only pymongo is a global
# conn is a class member, and would be accessed by doing mongoDB.conn
global conn
# with that being said, you're initializing a local variable here called conn
# that is not being stored anywhere - when this method finishes, this variable
# will be cleaned up from memory, what you are thinking you're doing here
# should be written as mongoDB.conn = pymongo.Connection("localhost", 27017)
conn = pymongo.Connection("localhost",27017)
def CreateCollection(name =""):
# there is one of two things you are trying to do here - 1, access a class
# level member called conn, or 2, access an instance member called conn
# depending on what you are going for, there are a couple of different ways
# to address it.
# all methods for a class, by default, are instance methods - and all of them
# need to take self as the first argument. An instance method of a class
# will always be called with the instance first. Your error is caused because
# you should declare the method as:
# def CreateCollection(self, name = ""):
# The alternative, is to define this method as a static method of the class -
# which does not take an instance but applies to all instances of the class
# to do that, you would add a @staticmethod decorator before the method.
# either way, you're attempting to access the global variable "conn" here,
# which again does not exist
# the second problem with this, is that you are trying to take your variable
# argument (name) and use it as a property. What python is doing here, is
# looking for a member variable called name from the conn object. What you
# are really trying to do is create a collection on the connection with the
# inputed name
# the pymongo class provides access to your collections via this method as a
# convenience around the method, create_collection. In the case where you
# are using a variable to create the collection, you would call this by doing
# conn.create_collection(name)
# but again, that assumes conn is what you think it is, which it isn't
dbCollection = conn.name
return dbCollection
if __name__ == '__main__':
# here you are just creating a pointer to your class, not instantiating it
# you are looking for:
# database = mongoDB()
database = mongoDB
# this is your error, because of the afore mentioned lack of 'self' argument
collection = database.CreateCollection("Hello")
我想看一下 Pep-8 (http://www.python.org/dev/peps/pep-0008/) 编码风格指南(非常有帮助)以了解如何编写代码以 Python 方式“流动”。
通过你的代码来解释发生了什么——这就是你最终想要做的:
import pymongo
class MongoDB: # Classes generally are camel-case, starting with uppercase
def __init__(self, dbname):
# the __init__ method is the class constructor, where you define
# instance members. We'll make conn an instance member rather
# than a class level member
self._conn = pymongo.Connection("localhost", 27017)
self._db = self._conn[dbname]
# methods usually start with lowercase, and are either camel case (less desirable
# by Python standards) or underscored (more desirable)
# All instance methods require the 1st argument to be self (pointer to the
# instance being affected)
def createCollection(self, name=""):
return self._db[name]
if __name__ == '__main__':
# you want to initialize the class
database = MongoDB("Hello")
collection = database.createCollection("MyTable")
鉴于此 - 编写此类包装器的目标是什么？同样可以写成:
import pymongo
conn = pymongo.Connection('localhost', 27017)
database = conn["Hello"]
collection = database["MyTable"]
如果您尝试创建一个更大的 API 来包裹 pymongo 数据库，那么我建议您查看一些已经构建的 ORM 模块。那里有一些 - 不能 100% 确定哪些可用于 MongoDB，但我使用的(我有偏见，我写的)称为 ORB，可以在 http://docs.projexsoftware.com/api/orb 找到
