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29 lines
1.3 KiB
Markdown
29 lines
1.3 KiB
Markdown
# Columns With Default Values Are Nil On Create
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Let's say I have a `MagicLinks` model backed by `magic_links` Postgres table.
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Both the `id` and `token` columns are of type `UUID` and have default values of
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`gen_random_uuid()`. That means from the Rails-side when I go to create a
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`MagicLink` record, I don't have to think about specifying values for `id` or
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`token` -- the DB will take care of that.
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```ruby
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> magic_link = MagicLink.create(expires_at: Time.zone.now, user: User.last)
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User Load (5.9ms) SELECT "users".* FROM "users" ORDER BY "users"."id" DESC LIMIT $1 [["LIMIT", 1]]
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TRANSACTION (0.1ms) BEGIN
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MagicLink Create (3.1ms) INSERT INTO "magic_links" ("user_id", "expires_at", "created_at", "updated_at") VALUES ($1, $2, $3, $4) RETURNING "id"
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...
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> magic_link.id
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=> "6c6dddbf-4427-407d-8dc8-eef8cb65d491"
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> magic_link.token
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=> nil
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```
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This `create` call is translated into an `insert` SQL statement that includes a
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`returning` clause. For `create` it is always `returning "id"`. This means that
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the `UUID` value generated in Postgres-land for `id` gets passed back into the
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ActiveRecord instance. The `UUID` value generated for `token`, however, is not
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because `token` isn't specified in the `returning` clause.
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[source](https://github.com/rails/rails/issues/17605)
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