【发布时间】：2019-12-06 14:06:23
【问题描述】：
我从表中获取问题对象
@issue = Issue.where(id: issue_id)
所以我有了下一个活动记录对象。
ActiveRecord::Relation::WhereClause:0x00007f88ea670f00 @predicates=[#<Arel::Nodes::Equality:0x00007f88ea670fa0 @left=#<struct Arel::Attributes::Attribute relation=#<Arel::Table:0x00007f88ea05fe68 @name="issues", @type_caster=#<ActiveRecord::TypeCaster::Map:0x00007f88ea05fee0 @types=Issue(id: integer, tracker_id: integer, project_id: integer, subject: string, description: text, due_date: date, category_id: integer, status_id: integer, assigned_to_id: integer, priority_id: integer, fixed_version_id: integer, author_id: integer, lock_version: integer, created_on: datetime, updated_on: datetime, start_date: date, done_ratio: integer, estimated_hours: float, parent_id: integer, root_id: integer, lft: integer, rgt: integer, is_private: boolean, closed_on: datetime)>, @table_alias=nil>, name="id">, @right=#<Arel::Nodes::BindParam:0x00007f88ea670fc8 @value=#<ActiveRecord::Relation::QueryAttribute:0x00007f88ea670ff0 @name="id", @value_before_type_cast=1, @type=#<ActiveRecord::ConnectionAdapters::SQLite3Adapter::SQLite3Integer:0x00007f88e6cd3950 @precision=nil, @scale=nil, @limit=nil, @range=-9223372036854775808...9223372036854775808>, @original_attribute=nil>>>]>}
使用 project_id: integer 列，但是当我尝试获取 project_id 值时 - 它引发了错误
我的代码：
project_id = @issue.project_id
错误：
NoMethodError (undefined method `project_id' for #<Issue::ActiveRecord_Relation:0x00007fdb03e0e008>
Did you mean? object_id):
【问题讨论】：
-
试试
Issue.where(id: issue_id).pluck(:project_id)。原因：where返回一个Issue::ActiveRecord_Relation（许多对象），project_id意味着在单个对象中调用。pluck获取对应于表列传递的每个参数，并在数组中返回它们。 -
@SebastianPalma 感谢您的注意，但已经阅读了 pluck 的内容，但仍然不明白如何将 project_id 从对象获取到变量。
-
如果你需要一条记录，那么你应该使用 find 而不是 where。试试
Issue.find(issue_id).project_id。 -
@SebastianPalma 是的，就是这样，SteveTurczyn 已经回答了
标签： ruby-on-rails ruby activerecord rails-activerecord