What do the on_delete options in Ecto.Migrations.r

2020-06-29 05:39发布

The Ecto documentation describes the options available to references/2, but does not document what those options do. The options available are:

  • :nothing
  • :delete_all
  • :nilify_all
  • :restrict

What do they do?

标签: elixir ecto
1条回答
啃猪蹄的小仙女
2楼-- · 2020-06-29 06:23

This is actually a SQL question at root.

https://github.com/elixir-ecto/ecto_sql/blob/52f9d27a7ad86442f442bad2f7ebd19ba09ddc61/lib/ecto/adapters/myxql/connection.ex#L902-L905

The PostgreSQL documentation outlines these options clearly:

  • :nothing - if any referencing rows still exist when the constraint is checked, an error is raised; this is the default behavior if you do not specify anything.
  • :delete_all - specifies that when a referenced row is deleted, row(s) referencing it should be automatically deleted as well
  • :nilify_all - causes the referencing column(s) in the referencing row(s) to be set to nil when the referenced row is deleted
  • :restrict - prevents deletion of a referenced row. It will fail if there is a referenced object.

:nothing and :restrict are similar but:

the essential difference between these two choices is that [:nothing] allows the check to be deferred until later in the transaction, whereas [:restrict] does not.

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