英文:
Is it possible to do select on preload in ecto query?
问题
我需要从 Post 模式中选择具有 10+ 个字段的特定字段。
我还需要选择预加载的 :comments。我该如何做到这一点？
查询 = 从 p in Post，预加载：[:comments]，选择：map(p，[:comments，:title])
Repo.all(query)
英文:
I need to select specific fields from the Post schema which have 10+ fields.
I need to select preloaded :comments as well. How can I do that?
query = from p in Post, preload: [:comments], select: map(p, [:comments, :title])
Repo.all(query)
答案1
得分: 2
有多种方法可以做到这一点，具体取决于您希望将什么样的数据结构作为输出。如果您想要一个仅包含 comments 和 title 字段的 %Post{} 结构体，请使用以下查询：
query = from p in Post, preload: [:comments], select:
Repo.all(query)
否则，请参考 select 查询表达式的文档说明 
英文:
There are multiple ways of doing this, depending on what kind of data structure you want to receive as output. If you want a %Post{} struct with only the comments and title fields, use the following query:
query = from p in Post, preload: [:comments], select:
Repo.all(query)
Otherwise, please refer to the documentation for the select query expression
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