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方法
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实例公共方法

except(*skips)

从查询中移除skips中指定的一个或多个条件。

Post.order('id asc').except(:order)                  # discards the order condition
Post.where('id > 10').order('id asc').except(:where) # discards the where condition but keeps the order

源代码：显示 | 在 GitHub 上 

# File activerecord/lib/active_record/relation/spawn_methods.rb, line 75
def except(*skips)
  relation_with values.except(*skips)
end

merge(other, *rest)

如果other是一个ActiveRecord::Relation，则合并other中的条件。如果other是一个数组，则返回一个数组，表示结果记录与other的交集。

Post.where(published: true).joins(:comments).merge( Comment.where(spam: false) )
# Performs a single join query with both where conditions.

recent_posts = Post.order('created_at DESC').first(5)
Post.where(published: true).merge(recent_posts)
# Returns the intersection of all published posts with the 5 most recently created posts.
# (This is just an example. You'd probably want to do this with a single query!)

Procs 将由 merge 评估

Post.where(published: true).merge(-> { joins(:comments) })
# => Post.where(published: true).joins(:comments)

这主要用于在多个关联之间共享公共条件。

对于两个关系中都存在的条件，来自other的条件将优先。要查找两个关系的交集，请使用QueryMethods#and。

源代码：显示 | 在 GitHub 上 

# File activerecord/lib/active_record/relation/spawn_methods.rb, line 33
def merge(other, *rest)
  if other.is_a?(Array)
    records & other
  elsif other
    spawn.merge!(other, *rest)
  else
    raise ArgumentError, "invalid argument: #{other.inspect}."
  end
end

only(*onlies)

从查询中移除除onlies中指定的一个或多个条件之外的所有条件。

Post.order('id asc').only(:where)         # discards the order condition
Post.order('id asc').only(:where, :order) # uses the specified order

源代码：显示 | 在 GitHub 上 

# File activerecord/lib/active_record/relation/spawn_methods.rb, line 83
def only(*onlies)
  relation_with values.slice(*onlies)
end