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首页 > 解决方案 > Ecto.Repo.delete/2：查看类型规范时，如何知道是否存在默认值？

elixir - Ecto.Repo.delete/2：查看类型规范时，如何知道是否存在默认值？

问题描述

这是类型规范：

iex(1)> h Ecto.Repo.delete
No documentation for function Ecto.Repo.delete was found, but there is a callback with the same name.
You can view callback documentations with the b/1 helper.

iex(2)> b Ecto.Repo.delete
@callback delete(
            struct_or_changeset :: 
              Ecto.Schema.t() | Ecto.Changeset.t(),
            opts :: Keyword.t()
          ) ::
            {:ok, Ecto.Schema.t()}
            | {:error, Ecto.Changeset.t()}

Deletes a struct using its primary key.

If the struct has no primary key,
Ecto.NoPrimaryKeyFieldError will be raised. If the struct
has been removed from db prior to call,
Ecto.StaleEntryError will be raised.

It returns {:ok, struct} if the struct has been
successfully deleted or {:error, changeset} if there was a
validation or a known constraint error.

## Options

  • :prefix - The prefix to run the query on (such as
    the schema path in Postgres or the database in MySQL).
    This overrides the prefix set in the query and any
    @schema_prefix set in the schema.
  • :stale_error_field - The field where stale errors
    will be added in the returning changeset. This option
    can be used to avoid raising Ecto.StaleEntryError.
  • :stale_error_message - The message to add to the
    configured :stale_error_field when stale errors happen,
    defaults to "is stale".

See the "Shared options" section at the module
documentation.

## Example

    post = MyRepo.get!(Post, 42)
    case MyRepo.delete post do
      {:ok, struct}       -> # Deleted with success
      {:error, changeset} -> # Something went wrong
    end

在最后的示例中，使用一个参数调用 delete()。而且，我可以delete()用一个参数成功调用：

  def delete_item(%Auction.Item{}=item) do
    @repo.delete(item)  #<=== HERE
  end

所以，这告诉我第二个参数必须有一个默认值。有没有办法以某种方式知道这一点？

标签： elixirphoenix-framework

解决方案

浏览文档和类似问题的答案，类型规范似乎不支持默认参数。这个 2014 年的 Github 问题解释了对此类功能的一些权衡。

怎么知道第二个参数是可选的？除了对 Elixir 代码进行源代码挖掘之外，希望它被记录在案。在这个版本的情况下Ecto.Repo.delete，参数opts在 typespec 中命名，并在标题“选项”下描述，这对我来说强烈暗示它们是可选的。

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