Ecto连接表验证

Question

我有一个名为：seasons_teams的连接表

  schema "seasons_teams" do
    field(:score, :integer)
    belongs_to(:season, Season, foreign_key: :season_id, type: :binary_id)
    belongs_to(:team, Team, foreign_key: :team_id, type: :binary_id)

    timestamps()
  end

这很好，但是我想验证一下season和team的副本是不可能存在的。

例如：

  %MyApp.SeasonsTeams{
    __meta__: #Ecto.Schema.Metadata<:loaded, "seasons_teams">,
    id: "89ec0dbd-cc61-4ba9-8dcf-b86b858d2882",
    inserted_at: ~N[2019-11-10 00:58:27],
    score: nil,
    season: #Ecto.Association.NotLoaded<association :season is not loaded>,
    season_id: "79c4bd04-d362-495c-ab13-649b299c23e2",
    team: #Ecto.Association.NotLoaded<association :team is not loaded>,
    team_id: "b6c408ef-d48e-4de9-8a46-8ae7bb12b699",
    updated_at: ~N[2019-11-10 00:58:27]
  },
  %MyApp.SeasonsTeams{
    __meta__: #Ecto.Schema.Metadata<:loaded, "seasons_teams">,
    id: "89a7fc61-6ce4-4a6d-a9dc-8e3494378e33",
    inserted_at: ~N[2019-11-10 00:58:37],
    score: nil,
    season: #Ecto.Association.NotLoaded<association :season is not loaded>,
    season_id: "79c4bd04-d362-495c-ab13-649b299c23e2",
    team: #Ecto.Association.NotLoaded<association :team is not loaded>,
    team_id: "b6c408ef-d48e-4de9-8a46-8ae7bb12b699",
    updated_at: ~N[2019-11-10 00:58:37]
  }

您可以看到这两个记录具有相同的season_id和相同的team_id，我不希望这成为可能。我很好奇Phoenix/Elixir/Ecto是否提供了一种很好的方法来处理这种情况？谢谢!

Answer 1

在该表上创建一个跨越两个字段的唯一索引，并使用unique_constraint验证唯一约束：

# In the migration
create unique_index(:seasons_teams, [:season_id, :team_id], name: :seasons_teams_season_id_team_id_index)

# In the changeset function
cast(season_team, params, [:season_id])
|> unique_constraint(:season_id, name: :seasons_teams_season_id_team_id_index)