小编Geo*_*iev的帖子

在我的 Rails 5.0.5 应用程序中，我需要将json列转换为string, array: true.

我的列中的值json如下：

[ "200px-RR5219-0015R.png", "2017_03_25_2235.doc", "137555.jpg" ]

我尝试过这个迁移：

[ "200px-RR5219-0015R.png", "2017_03_25_2235.doc", "137555.jpg" ]

并得到这个错误：

ActiveRecord::StatementInvalid: PG::DatatypeMismatch: ERROR:  column "attachments" cannot be cast automatically to type character varying[]
HINT:  You might need to specify "USING attachments::character varying[]".
: ALTER TABLE "tasks" ALTER COLUMN "attachments" TYPE character varying[]

然后我编辑了迁移：

class ChangeTaskAttachmentsTypeToString < ActiveRecord::Migration[5.0]
  def change
    change_column :tasks, :attachments, :string, array: true
  end
end

最后得到这个错误：

PG::CannotCoerce: ERROR:  cannot cast type json to …