英文:
I can't query GQL for 2 properties only wildcard is working
问题
我在Datastore中存储了comment实体，并使用Datastore Viewer查看存储的数据。
我可以执行以下查询：
select * from comment
select __key__ from comment
select Subject from comment
select Comment from comment
但是我无法执行以下查询：
select Subject, Comment from comment
// 错误：此查询的建议索引为：
// - kind: comment
// properties:
// - name: Comment
// - name: Subject
select __key__, Subject, Comment from comment
// 错误：不支持对属性 __key__ 进行投影
我找不到任何关于为什么出错的参考。这些错误信息并没有告诉我太多信息。
我没有为这些实体设置任何键或索引。
文档中提到了以下内容：
SELECT [DISTINCT] [* | <property list> | __key__]
[FROM <kind>]
[WHERE <condition> [AND <condition> ...]]
[ORDER BY <property> [ASC | DESC] [, <property> [ASC | DESC] ...]]
[LIMIT [<offset>,]<count>]
[OFFSET <offset>]
<property list> := <property> [, <property> ...]
<condition> := <property> {< | <= | > | >= | = | != } <value>
<condition> := <property> IN <list>
<condition> := ANCESTOR IS <entity or key>
<list> := (<value> [, <value> ...]])
Subject, Comment 是属性列表，是一个有效的查询。但实际上却不是。
我是用Go代码创建的实体。
英文:
I store comment entity in Datastore and I use Datastore Viewer to see stored data.
I can do following queries
select * from comment
select __key__ from comment
select Subject from comment
select Comment from comment
But I can't query
select Subject, Comment from comment
// Error: The suggested index for this query is:
// - kind: comment
// properties:
// - name: Comment
// - name: Subject
select __key__, Subject, Comment from comment
// Error: projections are not supported for the property: __key__
I can't find any reference why it is wrong. These errors does not tell me much.
I have not set any key or index for these entities.
Documentation tells following:
SELECT [DISTINCT] [* | <property list> | __key__]
[FROM <kind>]
[WHERE <condition> [AND <condition> ...]]
[ORDER BY <property> [ASC | DESC] [, <property> [ASC | DESC] ...]]
[LIMIT [<offset>,]<count>]
[OFFSET <offset>]
<property list> := <property> [, <property> ...]
<condition> := <property> {< | <= | > | >= | = | != } <value>
<condition> := <property> IN <list>
<condition> := ANCESTOR IS <entity or key>
<list> := (<value> [, <value> ...]])
Subject, Comment - is property list and it valid query. But it is not.
I created entity from Go code.
答案1
得分: 3
投影查询有一些限制。在projection-doc中提到了"只有索引属性可以进行投影"。
第一个错误消息明确显示了Subject, Comment的组合索引尚不存在。您可以通过在项目根文件夹的index.yaml中添加以下内容来手动创建索引：
- kind: comment
properties:
- name: Comment
- name: Subject
请参考index spec和projection-doc。
// 错误：不支持对属性进行投影：key
keys实体是通过GetAll方法返回的。不要将它们放在投影中。
keys, err := q.GetAll(c, &people)
我还不能发布超过2个链接，所以请在数据存储参考中查找更多详细信息。
英文:
The projection queries come with some limitations. In the projection-doc is mentioned that "Only indexed properties can be projected".
The first error message shows exactly that the combined index of Subject, Comment doesn't exist yet. You can create the index manually by adding
- kind: comment
properties:
- name: Comment
- name: Subject
to your index.yaml in your project root folder. Please have a look at the index spec and projection-doc.
// Error: projections are not supported for the property: __key__
Entity keys are returned by the GetAll method. Don't put them in your projection.
keys, err := q.GetAll(c, &people)
I can't post more than 2 links yet, so please look for more details in the datastore reference.
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