关于find方法中boolean型的问题

Question

关于find方法中boolean型的问题
悬赏：5 发布时间：2009-04-18 提问人：阿拉觉得方腊； (初级程序员)

Message.find(:first, :conditions => {:read => true})
=> #

为什么上面的方法可以，下面的方法就不行
其中t.column :read, :boolean
谢谢指点！

Message.find(:first, :conditions => ['read = ?', true])
ActiveRecord::StatementInvalid: Mysql::Error: You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'read = 1) LIMIT 1' at line 1: SELECT * FROM messages WHERE (read = 1) LIMIT 1
from /usr/lib/ruby/gems/1.8/gems/activerecord-2.2.2/lib/active_record/connection_adapters/abstract_adapter.rb:188:in log'
from /usr/lib/ruby/gems/1.8/gems/activerecord-2.2.2/lib/active_record/connection_adapters/mysql_adapter.rb:309:inexecute'
from /usr/lib/ruby/gems/1.8/gems/activerecord-2.2.2/lib/active_record/connection_adapters/mysql_adapter.rb:563:in select'
from /usr/lib/ruby/gems/1.8/gems/activerecord-2.2.2/lib/active_record/connection_adapters/abstract/database_statements.rb:7:inselect_all_without_query_cache'
from /usr/lib/ruby/gems/1.8/gems/activerecord-2.2.2/lib/active_record/connection_adapters/abstract/query_cache.rb:62:in select_all'
from /usr/lib/ruby/gems/1.8/gems/activerecord-2.2.2/lib/active_record/base.rb:635:infind_by_sql'
from /usr/lib/ruby/gems/1.8/gems/activerecord-2.2.2/lib/active_record/base.rb:1490:in find_every'
from /usr/lib/ruby/gems/1.8/gems/activerecord-2.2.2/lib/active_record/base.rb:1452:infind_initial'
from /usr/lib/ruby/gems/1.8/gems/activerecord-2.2.2/lib/active_record/base.rb:587:in `find'
from (irb):3
[b]问题补充：[/b]
我的问题是文什么上面的行，下面的不行。
而且我成功执行过，

Album.find(:first, :conditions => ['user_id = ? and id = ? and active = ?',1,3, true])
=> #

我感觉就是很矛盾很困惑，怎么有的可以，有的不可以，

Answer 1

问题在于：

   read这个字段名，也就是说你把字段名改成read1，再写就两种查询都可以用了。

那么，为什么read做字段名
[code="ruby"]Message.find(:first, :conditions => {:read => true}) [/code]

仍然，可以用呢？

因为，对于Rails而言，两种查询转换成的sql语句不太一样，

[code="ruby"]Message.find(:first, :conditions => ['read = ?', true]) [/code]
会转换成:
[code="sql"]SELECT * FROM messages WHERE (read = 1) LIMIT 1[/code]
这时就会有保留字做属性名的语法错误，当然，你把read改成read1是不会出错的。

但是，
[code="ruby"]Message.find(:first, :conditions => {:read => true})[/code]
会转换成
[code="sql"]SELECT * FROM messages WHERE (messages.read = 1) LIMIT 1[/code]
当然，就不会有属性名是保留字的错误。

至于
[code="ruby"]Album.find(:first, :conditions => ['user_id = ? and id = ? and active = ?',1,3, true]) [/code]
能执行，自然是因为，没有保留字的原因了。

:arrow: