present?基本上不是零,不是空的？

class Object
  def present?
    !blank?
  end
  def blank?
    respond_to?(:empty?) ? !!empty? : !self
  end
end

ActiveRecord条件

在Rails 4中,没有原始的sql代码就可以完成任务.

# Both lines lead to the same result:
User.where.not(name: [nil,""])
User.where.not(name: nil).where.not(name: "")

因为没有原始的sql代码,所以不必担心如果它们与每个数据库适配器一起使用.实际上,这对MysqL和postgres都有效.

to_sql

如果您附加了.to_sql,例如在rails控制台中,您可以看到它们如何转换为SQL查询.

# rails console

User.where.not(name: [nil,""]).to_sql
# => "SELECT \"users\".* FROM \"users\" WHERE (NOT ((\"users\".\"name\" = '' OR \"users\".\"name\" IS NULL)))"

User.where.not(name: nil).where.not(name: "").to_sql
# => "SELECT \"users\".* FROM \"users\" WHERE (\"users\".\"name\" IS NOT NULL) AND (\"users\".\"name\" != '')"

进一步阅读

> [1] Rails 4 guide “ActiveRecord Query Interface”
> [2] Definition of present? on github