Ruby-on-rails 仅当存在时才验证属性（仅当用户填写时）
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Validate attribute only if it present (only if user fill in it)
提问by prosto.vint
I need validate some attributes ONLY if they are not empty.
仅当某些属性不为空时，我才需要验证它们。
For example the user may have a logo. If we try to load it - validation should work. If we simply update the user's data without the logo, validation must be skipped.
例如，用户可能有一个标志。如果我们尝试加载它 - 验证应该有效。如果我们只是在没有徽标的情况下更新用户数据，则必须跳过验证。
Now i have:
我现在有：
The form has a choice of two files. One - logo, second - avatar. Both of this attributes is part of User model. In User model a have validation:
该表单可以选择两个文件。一个 - 标志，第二个 - 头像。这两个属性都是用户模型的一部分。在用户模型中有验证：
validates_preference_of :logo_file_name, :message=>I18n.t("...")
validates_format_of :logo_file_name, :with=>/\.(jpeg|jpg|png|gif)$/i, :message=> I18n.t("...")
validates_preference_of :avatar_file_name, :message=>I18n.t("...")
validates_format_of :avatar_file_name, :with=>/\.(jpeg|jpg|png|gif)$/i, :message=> I18n.t("...")
In this case, if we try to create a new User without selected logo and avatar, we will have errors (our validation). I tryed change validation and add ":on => :update" like this:
在这种情况下，如果我们尝试在没有选择徽标和头像的情况下创建新用户，则会出现错误（我们的验证）。我尝试更改验证并添加“：on => ：update”，如下所示：
validates_preference_of :logo_file_name, :message=>I18n.t("..."), :on => :update
validates_format_of :logo_file_name, :with=>/\.(jpeg|jpg|png|gif)$/i, :message=> I18n.t("..."), :on => :update
validates_preference_of :avatar_file_name, :message=>I18n.t("..."), :on => :update
validates_format_of :avatar_file_name, :with=>/\.(jpeg|jpg|png|gif)$/i, :message=> I18n.t("..."), :on => :update
Now i can create user without selected logo and avatar, but if i try edit user and try upload only logo - i have validation errors of avatar. If i choose file for avatar and logo leave blank - i have validation errors for logo.
现在我可以创建没有选定徽标和头像的用户，但是如果我尝试编辑用户并尝试仅上传徽标 - 我的头像验证错误。如果我为头像和徽标选择文件留空 - 我有徽标验证错误。
How i can run validation ony for attribute that I want to change?
如何对要更改的属性运行验证？
回答by Mark Thomas
Add :allow_blank => trueand it should do what you want.
添加:allow_blank => true它应该做你想做的。
回答by S?awosz
Maybe :if => lambda {|attr| attr.present?}will help?
也许:if => lambda {|attr| attr.present?}会有所帮助？
回答by miguel.camba
Some validations accept the options :allow_blank => trueor :allow_nil => true.
一些验证接受选项:allow_blank => true或 :allow_nil => true。
If this fails, use :if condition, like this:
如果失败，请使用 :if 条件，如下所示：
validates_format_of :avatar_file_name,
:with=>/\.(jpeg|jpg|png|gif)$/i,
:message=> I18n.t("..."),
:on => :update,
:if => lambda{ |object| object.avatar_file_name.present? }
But i encourage you to use allows. Much cleaner.
但我鼓励你使用允许。干净多了。
