虽然ActiveRecord是一个包含大量功能的庞然大物，但还是会时不时出现一些WTFs。其中一个WTF就是不支持SQLite中二进制列的默认值。
之前
让我们在一个使用SQLite数据库的模型中创建一个字符串列，并给它添加一个默认值。
# db/migrate/20220821142603_add_string_to_physician.rb
# class AddStringToPhysician < ActiveRecord::Migration[7.0]
# def change
# add_column :physicians, :signature, :string, default: "Regards"
# end
# end
irb(main):001:0> physician = Physician.create! name: "Belle"
...
irb(main):002:0> physician.signature
=> "Regards"
irb(main):003:0> physician.reload.signature
=> "Regards"
让我们对二进制列做同样的事情。
# db/migrate/20220821142330_add_greeting_to_physician.rb
# class AddGreetingToPhysician < ActiveRecord::Migration[7.0]
# def change
# add_column :physicians, :greeting, :binary, default: "Hello!"
# end
# end
irb(main):001:0> physician = Physician.create! name: "Belle"
(0.6ms) SELECT sqlite_version(*)
TRANSACTION (0.0ms) begin transaction
Physician Create (0.3ms) INSERT INTO "physicians" ("name", "created_at", "updated_at", "greeting", "signature") VALUES (?, ?, ?, ?, ?) [["name", "Belle"], ["created_at", "2022-08-21 15:47:44.957101"], ["updated_at", "2022-08-21 15:47:44.957101"], ["greeting", nil], ["signature", "Regards"]]
TRANSACTION (0.4ms) commit transaction
...
irb(main):002:0> physician.greeting
=> nil
irb(main):003:0> physician.reload.greeting
=> "Hello!"
这就造成了Sqlite与Rails行为的不一致。
之后
幸运的是，这个PR增加了对二进制列的默认值的支持，在从数据库中读取其数据之前就可以读取。
irb(main):001:0> physician = Physician.create! name: "Belle"
(0.6ms) SELECT sqlite_version(*)
TRANSACTION (0.0ms) begin transaction
Physician Create (0.3ms) INSERT INTO "physicians" ("name", "created_at", "updated_at", "greeting", "signature") VALUES (?, ?, ?, ?, ?) [["name", "Belle"], ["created_at", "2022-08-21 15:47:44.957101"], ["updated_at", "2022-08-21 15:47:44.957101"], ["greeting", "<11 bytes of binary data>"], ["signature", "Regards"]]
TRANSACTION (0.4ms) commit transaction
...
irb(main):002:0> physician.greeting
=> "Hello!"
irb(main):003:0> physician.reload.signature
=> "Hello!"
