多对多关系的变更集答案

【问题标题】：Changesets for many-to-many relationships多对多关系的变更集
【发布时间】：2017-06-22 13:40:52
【问题描述】：

与José's upserts post 一起，我在两个模式之间建立了多对多的关系——技术和工作是这样的：

defmodule JobJawn.Listing.Job do
  @moduledoc """
  A job is a position for which a JobJawn user might want to apply.  This is the
    central model for the system - meaning it's the reason a user might want to
    visit the system.
  """

  use Ecto.Schema

  alias JobJawn.Directory.Company
  alias JobJawn.Listing.{
          Discipline,
          EmploymentType,
          RoleType,
          Technology,
          Title}

  schema "listing_jobs" do
    field :date_missing, :naive_datetime
    field :name, :string
    field :url, :string

    belongs_to :company, Company
    belongs_to :discipline, Discipline
    belongs_to :employment_type, EmploymentType
    belongs_to :role_type, RoleType
    belongs_to :title, Title

    many_to_many :technologies,
                 Technology,
                 join_through: "listing_jobs_technologies"

    timestamps()
  end
end


defmodule JobJawn.Listing.Technology do
  @moduledoc """
  Technology serves as a tag to help JobJawn users interested in a certain
  technlogy (Elixir, Erlang, Python, C#, F#, etc) locate relevant positions
  """

  use Ecto.Schema

  schema "listing_technologies" do
    field :name, :string
    field :job_count, :integer, virtual: true

    many_to_many :jobs, JobJawn.Listing.Job, join_through: "listing_jobs_technologies"

    timestamps()
  end
end

为作业创建变更集时，我不断收到验证错误...

tech = JobJawn.Listing.Technology |> limit(1) |> JobJawn.Repo.one
JobJawn.Listing.Job
|> limit(1)
|> preload(:technologies)
|> JobJawn.Repo.one
|> change
|> put_assoc(:technologies, with: [tech])

会给我一个无效的变更集：

#Ecto.Changeset<action: nil, changes: %{},
 errors: [technologies: {"is invalid", [type: {:array, :map}]}],
 data: #JobJawn.Listing.Job<>, valid?: false>

我不知道为什么。

如果有帮助，这个 repo 是公开的：https://github.com/mcelaney/job_jawn/commit/f408505d165ae71947858676922cf067fe1cc413

【问题讨论】：

我认为对put_assoc的调用应该是：|> put_assoc(technologies, [tech])
呃 - 我是个白痴...
put_assoc 的语法与 cast_assoc 不同 - 您能否将其改写为答案以便我接受？

标签： elixir phoenix-framework ecto

【解决方案1】：

构建变更集应将[tech] 列表作为最后一个参数传递给put_assoc

tech = JobJawn.Listing.Technology |> limit(1) |> JobJawn.Repo.one

JobJawn.Listing.Job
|> limit(1)
|> preload(:technologies)
|> JobJawn.Repo.one
|> change
|> put_assoc(:technologies, [tech]) # <-- with: keyword removed

【讨论】：