python - App Engine 模型，get_or_insert 问题 w.r.t 主键和复合键

Question

A]问题总结:

我在模型之间有一对多的层次关系

国家 (1) --> 城市 (许多)
城市(1) --> 状态(多)

所以，只能有一个独特的国家，一个国家只能有一个独特的城市，一个城市可以有多种状态

我计划使用“get_or_insert”方法来确保我在数据库中维护唯一记录。

B] 代码摘录:

1]模型结构--

class UserReportedCountry(db.Model):
  name = db.StringProperty(required=True)

class UserReportedCity(db.Model):
  country = db.ReferenceProperty(UserReportedCountry, collection_name='cities')
  name = db.StringProperty(required=True)   

class UserReportedStatus(db.Model):
  city = db.ReferenceProperty(UserReportedCity, collection_name='statuses')
  status = db.BooleanProperty()
  date_time = db.DateTimeProperty(auto_now_add=True)

2] 用于存储从 HTML 表单检索到的数据的代码:

def store_user_data(self): 
  country_name = self.request.get('selCountry')
  user_reported_country = UserReportedCountry.get_or_insert(name=country_name)

  user_reported_city =  UserReportedCity.get_or_insert( name = self.request.get('city'), country = user_reported_country )

  user_reported_status = UserReportedStatus( status = self.request.get('status'), city = user_reported_city)
    user_reported_status.put()      

问题:

1] 从谷歌搜索中，似乎“get_or_insert”需要一个键，在我的“UserReportedCountry”模型中，我希望国家名称成为主键 在“UserReportedCity”模型中，我希望国家名称+城市名称的组合成为关键。我该怎么做？

2] 有没有办法在不指定 key 的情况下使用“get_or_insert”，我在 stackoverflow (http://stackoverflow.com/questions/4308002/google-app-engine-datastore-get- or-insert-key-name-confusion)，并尝试了这个想法，但没有奏效。

感谢阅读，

[编辑#1]

基于@Josh Smeaton 给出的响应的更改摘要

1] 现在代码检查用户报告的国家/地区是否存在于数据库中。如果用户报告的国家/地区不存在，则代码会创建一个 UserReportedCountry、UserReportedCity 并为其附加一个新状态

2] 如果存在国家/地区，则代码会检查用户报告的城市是否存在于给定国家/地区。

如果找不到城市，则创建一个城市记录并将其与找到的国家相关联并附上状态记录。

如果找到城市，则附上状态记录。

请求:

我将不胜感激，如果有人可以进行代码审查，如果我犯了任何错误，请告诉我。

谢谢，

代码摘录:

#this method will be used to parse the data the user provided in the html form and store it in the database models
#while maintaing the relationship between UserReportedCountry, UserReportedCity and UserReportedStatus
#BUG, there needs to be error checking to make sure the country , city and status data is invalid or not
#if the data is invalid, then error message needs to be reported and then redirection back to the main page
def store_user_data(self):
    #method call to find out the completly filled out UserReportedCity model
    user_reported_city = self.find_or_create_user_reported_country_and_city(
                                self.request.get('selCountry'), self.request.get('city'))

    #status is always unique for a user entry, so create a brand new UserReportedStatus everytime.
    user_reported_status = UserReportedStatus(status = self.get_user_reported_status(), city = user_reported_city)
    user_reported_status.put()            

#Here the code needs to find out if there is an existing country/city for the user selection
#1] If the user reported country doesnt exist, create a new country record, create a new city record and return the city record
#2] If the user reported country exists, check if the user reported city is associated with the country. 
#if the city exists, then return it. If the city doesnt exists, then create a new city and return it  
#example: if the user chooses USA, there needs to be a check if USA is already present or not, 
#so that we dont create an additonal USA record
def find_or_create_user_reported_country_and_city(self, country_name, city_name):
    country_query_result = db.GqlQuery("SELECT * FROM UserReportedCountry WHERE name = :country_name_value" 
                                       ,country_name_value = country_name).get()

    if (country_query_result == None):
        #since the country doesnt exists, create and save the country
        user_reported_country = self.create_and_save_user_country_record(country_name)

        #Since the country doesnt exist, there cannot be a city record for the given country, so blindly create the record
        return self.create_and_save_user_city_record(city_name, user_reported_country)
    else:
        #Since we found a country, now we need to find whether the user selected city exists for the given country
        return self.find_or_create_city_for_country(country_query_result, city_name)

#Check wheter the user selectred city exists in the country
#1] if the city exists return the record back 
#2] if the city doesnt exist creaty the city record and return it   
def find_or_create_city_for_country(self, country_record, city_name):
    city_query_result = db.GqlQuery("SELECT * FROM UserReportedCity WHERE name = :city_name_value AND country =:country_value"
                                     ,city_name_value = city_name, country_value = country_record ).get()

    if (city_query_result == None):
        #Since the city doesnt exist for the given country, 
        #create the city record, associated it with the country and return the record back
        return self.create_and_save_user_city_record(city_name, country_record)
    else:
        #since the city was found, return the record back 
        return city_query_result    

#method to create a UserReportedCountry record for a given country name 
def create_and_save_user_country_record(self, country_name):
    user_reported_country = UserReportedCountry(name= country_name)
    user_reported_country.put()
    return user_reported_country

#method to create a UserReportedCity record for a given city name and a given country record
def create_and_save_user_city_record (self, city_name, country_record):
    user_reported_city = UserReportedCity(name = city_name, country = country_record)
    user_reported_city.put()
    return user_reported_city

[编辑#2]

在 html 表单中，保存数据的调用是使用“post”完成的。您认为这仍然是一个问题吗？

<div id="userDataForm">
    <form method="post" action="/UserReporting">
      <p> Select Country: </p>
      <select name="selCountry" id="country">
      <!-- By default, we will select users country -->
      <script type="text/javascript" language="JavaScript">
            document.write("<option value=\"" + geoip_country_name() + "\" selected>"
      </script>
      :
      :
      :
      <p> Select City: </p>
      <div>
        <input type="text" name="city" id="city"> 

        <!-- By default, we will select users city -->
        <script type="text/javascript" language="JavaScript">
            document.getElementById("city").value = geoip_city()
        </script>

      </div>    

      <input type="submit" name="report_down" value="Report Down">
      <input type="submit" name="report_up" value="Report Up"> 
    </form>
<div>           

最初我尝试使用 Djangoforms，但我被阻止了，因为我不知道如何使用 javascript 在 djangoform 中选择一个值

Answer 1

按顺序回答您的问题:

1] From the google search, it appears "get_or_insert" requires a key, In my case in the "UserReportedCountry" model, i want the name of the country to be the primary key and in the "UserReportedCity" model, i want the combination of country name + city name to be the key. How do i go about doing this ?

只需指定国家名称，以及国家和城市的串联(例如“美国/旧金山”作为您传递给 get_or_insert 的键名称。顺便说一句，get_or_insert 只是以下内容的语法糖:

def get_or_insert(cls, key_name, **kwargs):
  def _tx():
    obj = cls.get_by_key_name(key_name)
    if obj is None:
      return cls(key_name, **kwargs)
    else:
      return obj
  return db.run_in_transaction(_tx)

2] Is there a way to use "get_or_insert" without specifying a key, I came accross the following posting on stackoverflow (http://stackoverflow.com/questions/4308002/google-app-engine-datastore-get-or-insert-key-name-confusion), and tried the idea but it didnt work.

这样做真的没有意义。键是 App Engine 中模型的唯一唯一字段，您不能在 App Engine 中执行跨实体组查询，因此除非您指定一个，否则不可能执行事务性获取或插入操作。不过，根据您的要求，使用国家/地区名称和城市名称作为键名称应该可以正常工作。