Ecto 为查询声明模式

Question

我正在尝试运行此查询：

select last_sd.*
from
  (select distinct(sensor_id) from sensor_data) s LEFT JOIN LATERAL
  (select * from sensor_data sd1 where sd1.sensor_id = s.sensor_id order by sd1.received_at desc limit 1) last_sd ON true

我得到的最接近的是：

from s in IotInABox.SensorData, distinct: true, select: s.sensor_id
|> join(:left_lateral, [s], sd in fragment("select * from sensor_data sd1 where sd1.sensor_id = ? order by sd1.received_at desc limit 1", s.sensor_id))
|> select([s, sd], sd)

然而这部分工作，因为它抛出

PostgreSQL requires a schema module when using selector "f1" but none was given. Please specify a schema or specify exactly which fields from "f1" you desire in query

意思是因为我没有from s in SensorData它不知道要使用哪个ecto模型，

有没有办法告诉 ecto 使用哪个模式作为查询结果？

Answer 1

也许不完美，但这样的东西对我有用（在下面的示例中使用我项目中的名称）：

keys = Division.__schema__(:fields)
query = from d in "divisions", select: map(d, ^keys)
result = Repo.all(query) |> Enum.map(&(struct(Division, &1)))

1. 首先您需要架构字段列表
2. 选择地图形式的所有键
3. 将地图映射回结构 ^^