ActiveRecord.find方法中":conditions"的应用

在SQL文的查询条件中经常会用得到关键字in，例如：

SELECT * FROM accounts WHERE nick_name = 'nicknm' AND id IN ("1","2");

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此时如果利用Rails的find方法，代码如下所示：

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require "rubygems"require "active_record"module ActiveRecordclass Basedef self.each_cons(n)offset = 0loop dosize = yield(offset)break if size < noffset += nendendendendActiveRecord::Base.establish_connection(:adapter => 'mysql',:host => 'localhost',:database => 'myapp_development',:username => 'my',:password => '123')class Account < ActiveRecord::Baseestablish_connection(:adapter => 'mysql',:host => 'localhost',:database => 'myauth_development',:username => 'my',:password => '123')end#condns 是个数组condns = []condns << "1"condns << "2"#非常值得注意的是：此时传给in(即第二个？)的参数一定要是数组类型的，#否则返回的不是想要的结果。#举例说明：如果将condns设置成字符串类型→"1,2"，那么下述find方法解析完的#SQL是SELECT * FROM accounts WHERE nick_name = 'nicknm' AND id #IN ("1,2");#而我们期待的结果应该是：#SELECT * FROM accounts WHERE nick_name = 'nicknm' AND id IN #("1","2");accounts = Account.find(:all, :conditions => ["nick_name = ? and id in (?)",  "nicknm",  condns],:order => 'id asc',:limit => 1000)