elixir - 在 Phoenix 中使用 Ecto 获取数据时仅获取特定字段

Question

我正在尝试在我在 Phoenix 的 API 调用之一中返回一些 JSON 数据。我正在获取 Subject 的所有记录并发送它们但是 Ecto返回一些我不想要的额外字段。

我可以做什么:

仅获取特定属性(例如仅 id 和 name )

不要在我的回复中获取不必要的字段(例如 __meta__ 和 __owner__ )

这是我的 Controller :

# Controller
def index(conn, _) do
    subjects = Subject |> Repo.all
    conn |> render subjects: subjects
end

这是我的 View :

# View
def render("index.json", %{subjects: subjects}) do
    subjects
end

这是我的回应:

[
    {
        "teachers": {
            "__owner__": "Elixir.MyApp.Subject",
            "__field__": "teachers",
            "__cardinality__": "many"
        },
        "updated_at": "2015-06-20T15:32:20Z",
        "topics": {
            "__owner__": "Elixir.MyApp.Subject",
            "__field__": "topics",
            "__cardinality__": "many"
        },
        "name": "Physics",
        "inserted_at": "2015-06-20T15:32:20Z",
        "id": 1,
        "__meta__": {
            "state": "loaded",
            "source": "subjects"
        }
    },
    {
        "teachers": {
            "__owner__": "Elixir.MyApp.Subject",
            "__field__": "teachers",
            "__cardinality__": "many"
        },
        "updated_at": "2015-06-20T15:37:59Z",
        "topics": {
            "__owner__": "Elixir.MyApp.Subject",
            "__field__": "topics",
            "__cardinality__": "many"
        },
        "name": "Chemistry",
        "inserted_at": "2015-06-20T15:37:59Z",
        "id": 2,
        "__meta__": {
            "state": "loaded",
            "source": "subjects"
        }
    },
    {
        "teachers": {
            "__owner__": "Elixir.MyApp.Subject",
            "__field__": "teachers",
            "__cardinality__": "many"
        },
        "updated_at": "2015-06-20T15:38:41Z",
        "topics": {
            "__owner__": "Elixir.MyApp.Subject",
            "__field__": "topics",
            "__cardinality__": "many"
        },
        "name": "Mathematics",
        "inserted_at": "2015-06-20T15:38:41Z",
        "id": 3,
        "__meta__": {
            "state": "loaded",
            "source": "subjects"
        }
    },
    {
        "teachers": {
            "__owner__": "Elixir.MyApp.Subject",
            "__field__": "teachers",
            "__cardinality__": "many"
        },
        "updated_at": "2015-06-22T15:40:17Z",
        "topics": {
            "__owner__": "Elixir.MyApp.Subject",
            "__field__": "topics",
            "__cardinality__": "many"
        },
        "name": "Biology",
        "inserted_at": "2015-06-22T15:40:17Z",
        "id": 4,
        "__meta__": {
            "state": "loaded",
            "source": "subjects"
        }
    }
]

Answer 1

将您的 View 更改为:

def render("index.json", %{subjects: subjects}) do
  Enum.map(subjects, &Map.take(&1, [:id, :name]))
end

此外，您还可以通过将 Controller 更改为以下内容来要求 Ecto 返回字段的子集:

def index(conn, _) do
  subjects = from(s in Subject, select: %{id: s.id, name: s.name}) |> Repo.all
  conn |> render subjects: subjects
end