活动模型序列化器-自定义响应

Question

我正在尝试为以下项自定义序列化器：

# in DB
{
  "id": 1,
  "measurement": 10.5,
  "sequence": 1,
  "time_stamp": "2016-05-25T04:53:38.000Z",
  "device_id": 2,
  "patient_id": 3,
  "measurement_type": "ecg"
},
{
  "id": 2,
  "measurement": 20.5,
  "sequence": 2,
  "time_stamp": "2016-05-25T04:53:38.000Z",
  "device_id": 2,
  "patient_id": 3,
  "measurement_type": "ecg"
}
{
  "id": 3,
  "measurement": 30.5,
  "sequence": 3,
  "time_stamp": "2016-05-25T04:53:38.000Z",
  "device_id": 2,
  "patient_id": 3,
  "measurement_type": "ecg"
}

# need to return this structure via GET
{
  "max_timestamp": "2020-05-25T04:53:38.000Z",
  "measurement_type": "ecg",
  "measurements": [
    { measurement: 10.5, sequence: 1, time_stamp: "2020-05-25T04:53:38.000Z" },
    { measurement: 20.5, sequence: 2, time_stamp: "2016-05-25T04:53:38.000Z" },
    { measurement: 30.5, sequence: 3, time_stamp: "2012-05-25T04:53:38.000Z" }
  ]
}

目前我有这个：

class PatchDataSerializer < ActiveModel::Serializer
  attributes :max_timestamp, :measurement_type, :measurements

  def measurements
    [{ :measurement => object.measurement, :sequence => object.sequence, :time_stamp => object.time_stamp.to_i }]
  end

  def max_timestamp
  end

end

正在返回：

[
  {
    "max_timestamp": null,
    "measurement_type": "ecg",
    "measurements": [
      {
        "measurement": 20.5,
        "sequence": 5,
        "time_stamp": 1464152018
      }
    ]
  },
  {
    "max_timestamp": null,
    "measurement_type": "ecg",
    "measurements": [
      {
        "measurement": 20.5,
        "sequence": 5,
        "time_stamp": 1464152018
      }
    ]
  }
]

如您所见，这不起作用。 我最大的问题是如何将每一行的measurements推入一个阵列中？ 我还需要为整个请求而不是每一行返回一次max_timestamp 。

任何帮助是极大的赞赏。

Answer 1

您可以为要序列化的类创建一个自定义类方法，如下所示（我假设您要按类型进行过滤？）

def self.measurements_of_type(type)
  {
    max_timestamp: Class.maximum(:time_stamp),
    measurement_type: type
    measurements: Class.where(type: type).select(:measurement, :sequence, :time_stamp)
  }
end

Answer 2

在我看来，您可以创建一个新类来处理来自测量的数据聚合，然后为该类创建一个序列化器。

取决于您所使用的AMS版本，可以采用不同的方式进行操作，但要点很明显

class MeasurementsAggregation
  attr_reader :measurements, :type, :max_timestamp

  def initialize(type, measurements)
    @measurements = measurements
    @max_timestamp = measurements.max_by(&:updated_at).updated_at
    @type = type
  end
end

那么您的序列化器将是

class MeasurementsAggregationSerializer < ActiveModel::Serializer
  attributes :max_timestamp, :type

  has_many :measurements, serializer: MeasurementSerializer
end

您的测量序列化器将是

class MeasurementSerializer < ActiveModel::Serializer
  attributes :measurement, :sequence, :time_stamp
end

您可能需要做一些调整才能使PORO与AMS一起工作，但这应该是它的要旨。