postgresql - Ecto， Phoenix : How to update a model with an embeds_many declaration?

Question

我有两个模型，Owner 和 Property，其中 Owner 的模式有一个 embeds_many声明，像这样:

defmodule MyApp.Owner do
  use MyApp.Web, :model

  alias MyApp.Property

  schema "owners" do
    field name, :string
    embeds_many :properties, Property
    timestamps()
  end

  @doc """
  Builds a changeset based on the `struct` and `params`.
  """
  def changeset(struct, params \\ %{}) do
    struct
    |> cast(params, [])
    |> validate_required([])
  end
end

还有这个:

defmodule MyApp.Property do
  use MyApp.Web, :model

  embedded_schema do
    field :name, :string
    field :value, :float, default: 0
  end

  def changeset(struct, params \\ %{}) do
    struct
    |> cast(params, [:name, :value])
    |> validate_required([:name])
  end
end

migration我正在使用的是:

defmodule MyApp.Repo.Migrations.CreateOwner do
  use Ecto.Migration

  def down do
    drop table(:owners)
  end

  def change do
    drop_if_exists table(:owners)
    create table(:owners) do
      add :name, :string
      add :properties, :map
      timestamps()
    end
  end
end

还有一个可能的 seed是:

alias MyApp.{Repo, Owner, Property}

Repo.insert!(%Owner{
  name: "John Doe",
  properties: [
    %Property{
      name: "Property A"
    },
    %Property{
      name: "Property B",
      value: 100000
    },
    %Property{
      name: "Property C",
      value: 200000
    }
  ]
})

最后，我的问题是:如何将 John Doe 的 Property C 的值从 200000 更新为 300000 ？如果 John Doe 购买了 Property D:

%Property{
  name: "Property D"
  value: 400000
}

我如何将其添加到他在数据库中的 properties 中？ (我正在使用 Postgres )。

Answer 1

最简单的方法是获取记录，更新属性列出并保存更改:

owner = Repo.get!(Owner, 1)
properties = owner.properties

# update all properties with name "Property C"'s value to 400000
properties = for %Property{name: name} = property <- properties do
  if name == "Property C" do
    %{property | value: 400000}
  else
    property
  end
end

# add a property to the start
properties = [%Property{name: "Property D", value: 400000} | properties]

# or to the end
# properties = properties ++ [%Property{name: "Property D", value: 400000}]

# update
Owner.changeset(owner, %{properties: properties})
|> Repo.update!

您可以使用 JSON functionsprovided by PostgreSQL 执行一些操作(至少插入一个属性)使用fragment 但我认为您不能搜索并有条件地更新项目使用它们的数组。