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Gaelyk教程为数据存储提供了一些不错的低级包装器，这篇 Gaelyk 谷歌组文章描述了一种简单的建模关系的方法，只需将键存储在实体的集合中。

我的问题是如何对集合中的值执行查询？这是一些示例代码来澄清......

def b1 = new Entity("Book")
b1.title = "Book1"
b1.save()

def b2 = new Entity("Book")
b2.title = "Book2"
b2.save()

def author1 = new Entity("Author")  
author1.books = [b1.key, b2.key]
author1.name = "Chris"
author1.save()

// It is easy to simply query the Author entity for a standard string property
def query = new Query("Author")
query.addFilter("name", Query.FilterOperator.EQUAL, "Chris")
PreparedQuery preparedQuery = datastore.prepare(query)
def authors = preparedQuery.asList(withLimit(1))
assert authors[0].name == "Chris"

// But I can't find out how to query a collection property eg books on the Author entity
def query2 = new Query("Author")
// I would like to do something to return the entity if the value is in the collection property
// eg if there could be something like 'CONTAINS' criteria ...
// Unfortunately Query.FilterOperator.CONTAINS doesn't exist...
query2.addFilter("books", Query.FilterOperator.CONTAINS, b2.key)
PreparedQuery preparedQuery2 = datastore.prepare(query2)
def authors2 = preparedQuery2.asList(withLimit(1))
assert authors2[0].name == "Chris"

如何创建在实体的集合属性中搜索匹配项的查询？即如何重新创建上面神话般的“FilterOperator.CONTAINS”查询的功能？

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3 回答 3

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只是为了将来用户登陆此页面而回答：

Query.FilterOperator.EQUAL也会在键列表中找到（CONTAINS如果是列表，它的作用是 ）。所以现在你的第二个案例看起来像：

def query2 = new Query("Author")
query2.addFilter("books", Query.FilterOperator.EQUAL, b2.key)
PreparedQuery preparedQuery2 = datastore.prepare(query2)
def authors2 = preparedQuery2.asList(withLimit(1))
assert authors2[0].name == "Chris"

并且断言通过了:)

乍一看这可能看起来很奇怪，但它确实是 DataStore 的一个很棒的特性。

于 2011-08-02T18:14:18.827 回答
3

一种方法是将作者键作为实体“Book”中的字段之一。因此，您可以先查询该书，然后再获取该书的作者。

def author1 = new Entity("Author")  
author1.name = "Chris"
author1.save()

def b1 = new Entity("Book")
b1.title = "Book1"
b1.authors = [author1.key]
b1.save()

author1.books = [ b1.key ]
author1.save()

def book = datastore.get(b1.key)    
def chrisAuthors = book.authors.findAll { authorKey -> datastore.get(authorKey).name == 'Chris' }
assert chrisAuthors.size() == 1
于 2011-02-05T20:09:58.813 回答
2

顺便说一下，关于这个主题的一点更新：您可能想看看最近发布的 Gaelyk 1.0 的新 Query DSL 功能。

http://gaelyk.appspot.com/tutorial/app-engine-shortcuts#query

这应该会简化许多可以对数据存储进行的查询。

于 2011-08-31T07:23:09.363 回答