Ruby-on-rails 在 Rails 4 中使用 has_many :through :uniq 时的弃用警告
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Deprecation warning when using has_many :through :uniq in Rails 4
提问by Ryan Crispin Heneise
Rails 4 has introduced a deprecation warning when using :uniq => true with has_many :through. For example:
当使用 :uniq => true 和 has_many :through 时，Rails 4 引入了弃用警告。例如：
has_many :donors, :through => :donations, :uniq => true
Yields the following warning:
产生以下警告：
DEPRECATION WARNING: The following options in your Goal.has_many :donors declaration are deprecated: :uniq. Please use a scope block instead. For example, the following:
has_many :spam_comments, conditions: { spam: true }, class_name: 'Comment'
should be rewritten as the following:
has_many :spam_comments, -> { where spam: true }, class_name: 'Comment'
What is the correct way to rewrite the above has_many declaration?
重写上述 has_many 声明的正确方法是什么？
回答by Dylan Markow
The uniqoption needs to be moved into a scope block. Note that the scope block needs to be the second parameter to has_many(i.e. you can't leave it at the end of the line, it needs to be moved before the :through => :donationspart):
该uniq选项需要移动到作用域块中。请注意，scope 块需要是第二个参数 to has_many（即您不能将它留在行尾，它需要移动到:through => :donations部件之前）：
has_many :donors, -> { uniq }, :through => :donations
It may look odd, but it makes a little more sense if you consider the case where you have multiple parameters. For example, this:
这可能看起来很奇怪，但如果您考虑有多个参数的情况，它会更有意义。例如，这个：
has_many :donors, :through => :donations, :uniq => true, :order => "name", :conditions => "age < 30"
becomes:
变成：
has_many :donors, -> { where("age < 30").order("name").uniq }, :through => :donations
回答by Andrew Hacking
In addition to Dylans answer, if you happen to be extending the association with a module, make sure that you chain it in the scope block (as opposed to specifying it separately), like so:
除了 Dylans 答案之外，如果您碰巧扩展了与模块的关联，请确保将其链接到作用域块中（而不是单独指定它），如下所示：
has_many :donors,
-> { extending(DonorExtensions).order(:name).uniq },
through: :donations
Maybe its just me but it seems very unintuitive to use a scope block to extend an association proxy.
也许它只是我，但使用范围块来扩展关联代理似乎非常不直观。
