如何通过键选择单个实体（低级java数据存储区API） [英] How to select a single Entity by key (low level java datastore API)

问题描述

我对如何创建一个Key对象来选择我的实体（Customer）的一行有点困惑。

我的代码：

 查询查询=新查询（客户）; 
 // ****我该如何创建这个键？ 
 Key key = KeyFactory.createKey（Customer，1）; 
 // **** 
 FilterPredicate keyFilter = new FilterPredicate（Entity.KEY_RESERVED_PROPERTY，FilterOperator.EQUAL，key）; 
 query.setFilter（keyFilter）; 
 DatastoreService datastore = DatastoreServiceFactory.getDatastoreService（）; 
 PreparedQuery pq = datastore.prepare（query）; 
实体客户= pq.asSingleEntity（）; 
 if（！（customer == null））{
 log.info（OK！）; 
} 
 else {
 log.info（找不到客户）; 
} 
  

我的结果总是：找不到客户。

使用数据存储区查看器（我在本地工作）可以看到3行：

• id / name = 1 email =your emailname =your name


• id / name = 2 email =your emailname =your name $ b
• id / name = 3 email =您的电子邮件地址name =您的姓名

id / name = 1。
我试过了：
KeyFactory.createKey（Customer，1）;
和
KeyFactory.createKey（Customer，your name）;

但没有成功。

当我以编程方式在Customer上搜索（asList）并打印出键值时，我看到：

• 第1行key =客户（您的姓名）/客户（1）


• 第2行key =客户
  
• row 3 key = Customer（your name）/ Customer（3）

可打印的值这些键的格式为：实体（名称）/实体（ID /名称）

如何在我的代码中创建此类键值？
在javadoc上我只看到：
$ b $ ul
createKey（kind，id）

createKey（kind，name）

其他方法需要祖先，我没有创建祖先。 ...
这是我创建3行的代码（已执行3次）：

  Key customerKey = KeyFactory.createKey（Customer，your name）; 
实体客户=新实体（客户，customerKey）; 
 customer.setProperty（name，your name）; 
 customer.setProperty（email，你的电子邮件）; 
 DatastoreService datastore = DatastoreServiceFactory.getDatastoreService（）; 
 datastore.put（customer）; 
  

致谢！

/ p>

最大值

换句话说，如何创建一个其toString给出以下结果的Key ？

• 代码：log.info（customer KeyFactory.keyToString =+ KeyFactory.keyToString（key））; / li>
  
• 输出：INFO：customer KeyFactory.keyToString = Customer（your name）/ Customer（1）
  
  =h2_lin>解决方案

  实体的创建不正确。
  您不必自己创建密钥。
  如果您使用kind和keyname或ID参数创建一个实体，则会自动从该种类和键名或ID中创建一个键。

   实体客户=新实体（客户，您的姓名）; 
   customer.setProperty（email，你的电子邮件）; 
   
   DatastoreService datastore = DatastoreServiceFactory.getDatastoreService（）; 
   datastore.put（customer）; 
    

  这就是您需要创建所需实体的全部功能。

  
  
  

  当您给出一种和一个键时，将创建一个子实体。
  因此，您创建了一个带有您的姓名的客户，他是ID为1的客户。

  
  
  

  要使用密钥获取实体，您只需要使用相同的参数来创建一个键。

    Key key = KeyFactory.createKey（Customer，your name）; 
    

  我宁愿使用get（），但我不知道你想要做什么。
  举例来获取客户的电子邮件：
  
  

   实体e; 
  尝试{
   e = datastore.get（key）; 
   
   String myEmail =（String）e.getProperty（your email）; 
    

  
  

  I'm a bit confused on how to create a "Key" object to select exactly 1 row of my Entity ("Customer").

  My code :

  Query query = new Query("Customer");
  // **** how do I have to create this key ???
  Key key = KeyFactory.createKey("Customer", 1);
  // ****
  FilterPredicate keyFilter =  new FilterPredicate(Entity.KEY_RESERVED_PROPERTY,       FilterOperator.EQUAL, key);
  query.setFilter(keyFilter);
  DatastoreService datastore = DatastoreServiceFactory.getDatastoreService();
  PreparedQuery pq = datastore.prepare(query);
  Entity customer = pq.asSingleEntity();
  if  (! (customer == null)) {
      log.info("OK !");
  }
  else {
      log.info("no customer found");
  }
  

  My result is always : "no customer found".

  With the datastore viewer (I'm working locally) I can see 3 rows :

  • id/name = 1 email = "your email" name = "your name"
  • id/name = 2 email = "your email" name = "your name"
  • id/name = 3 email = "your email" name = "your name"

  I want to select customer with id/name=1. I've tried : KeyFactory.createKey("Customer", 1); and KeyFactory.createKey("Customer", "your name");

  but with no success.

  When I do programmatically a search (asList) on "Customer" and I print the keys' values I see :

  • row 1 key = Customer("your name")/Customer(1)
  • row 2 key = Customer("your name")/Customer(2)
  • row 3 key = Customer("your name")/Customer(3)

  The printable values of the keys are in the format : "Entity(name)/Entity(id/name)"

  How can I create such key values in my code ? On the javadoc I see only :

  • createKey("kind", id)
  • createKey("kind", "name")

  The other methods require an ancestor, I've not created an ancestor .... This is the code that I've executed to created the 3 rows (it has been executed 3 times) :

  Key customerKey = KeyFactory.createKey("Customer", "your name");
  Entity customer = new Entity("Customer", customerKey);
  customer.setProperty("name", "your name");
  customer.setProperty("email", "your email");
  DatastoreService datastore = DatastoreServiceFactory.getDatastoreService();
  datastore.put(customer);
  

  Thanks in advance !

  Regards

  Max

  In other words, how do create a Key whose "toString" gives the following result ?

  • Code : log.info("customer KeyFactory.keyToString = "+KeyFactory.keyToString(key));
  • Output : INFO: customer KeyFactory.keyToString = Customer("your name")/Customer(1)

  解决方案

  The creation of the Entities is not correct. You dont have to create a key on your own. If you create a Entity with a kind and keyname or ID parameter, a key will be created automaticlly out of the kind and the keyname or ID.

  Entity customer = new Entity("Customer", "your name");
  customer.setProperty("email", "your email");
  
  DatastoreService datastore = DatastoreServiceFactory.getDatastoreService();
  datastore.put(customer);
  

  That is all you need to create the Entity you want.

  When you give a kind and a key, a child Entity will be created. So you had created a Customer with "your name" who is a Customer with the ID 1.

  To get the Entity with a key you just have to take the same parameters to create a key.

  Key key = KeyFactory.createKey("Customer", "your name");
  

  I would prefer to use get(), but i dont know what you want to do. For Example to get the email of a Customer:

      Entity e;
      try {
          e = datastore.get(key);
  
          String myEmail= (String) e.getProperty("your email");
  

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