在 Phoenix 中使用 Ecto 获取数据时仅获取特定字段

Question

我正在尝试 return 一些 JSON 数据到我在凤凰城的一个 API 电话中。我正在获取 Subject 的所有记录并发送它们，但是 Ecto return 有一些我不想要的额外字段。

我能做什么：

仅获取特定属性（例如，仅 id 和 name）
我的回复中没有出现不必要的字段（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

这是我的回复：

[
    {
        "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

将您的观点更改为：

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

此外，您还可以要求 Ecto return 将控制器更改为以下字段的子集：

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

在 Phoenix 中使用 Ecto 获取数据时仅获取特定字段

Get only specific fields when fetching data using Ecto in Phoenix

elixir

ecto

phoenix-framework