valid? 方法会清空errors

gistfile1.txt

>> c.errors.add_on_blank('instructor','not be blank')
=> ["instructor"]
>> c.errors
=> #<ActiveRecord::Errors:0xb01f150c @errors={"instructor"=>["not be blank"]}, @base=#<Conversation id: "3e7f4481-e96b-012d-7fdc-042b2b5ce4fb", state: 10, tag: "20101214-2-00022", title: "死亡索赔", aim: 1, emergency: 1, security: 1, kind_id: 1, content: "当事人利爱琼称有29人来我厂索赔，事�...", record_id: nil, district: "440310008000", ownerdistrict: "440310008000", sub_kind_id: 199, place: "坑梓", source: 3, reportor_id: "3e7f4480-e96b-012d-7fdc-042b2b5ce4fb", reported_at: "2010-12-14 12:46:00", levels: 2, finishdate: "2011-01-27 00:00:00", advice: "请司法所处理,并将处理结果于15个工作...", remark: nil, flag: 1, creator_id: "57ec3557-c4dc-4ac8-87a6-a13ad4104686", modifier_id: "57ec3557-c4dc-4ac8-87a6-a13ad4104686", dispatched_at: "2010-12-16 18:29:35", finished_at: nil, created_at: "2010-12-14 12:47:57", updated_at: "2010-12-31 17:59:31", count: nil, grid_id: nil, building_id: nil, warndate: "2011-01-25 00:00:00", dealdistrict: "440310008000", instruct: "同意拟办意见.", is_instruct: 0, advicer_id: "39022d40-e97c-012d-8003-042b2b5ce4fb", department_id: "68061b50-d28a-012d-c214-001321c95b62", serial_dep: nil, instructor_id: nil, utag: "10008201012A99023">>
>> c.errors.empty?
=> false
>> c.errors.empty?
=> false
>> c.errors.empty?
=> false
>> c.errors.empty?
=> false
>> c.valid?
=> true
>> c.errors.empty?
=> true