ThinkPHP CURD方法的field方法属于模型的连贯操作方法之一,主要目的是标识要返回或者操作的字段,可以用于查询和写入操作。
1、用于查询
在查询操作中field方法是使用最频繁的。
$Model->field('id,title,content')->select();
这里使用field方法指定了查询的结果集中包含id,title,content三个字段的值。执行的SQL相当于:
SELECT id,title,content FROM table
当然,除了select方法之外,所有的查询方法,包括find等都可以使用field方法,这里只是以select为例说明。
上面的例子也可以使用数组代替:
$Model->field(array('id','title','content'))->select();
最终执行的SQL和上面等效。
似乎看起来数组的用法过于复杂,不过先别下这个结论,后面就会明白数组用法的好处了。
数组方式的定义可以为某些字段定义别名,例如:
$Model->field(array('id','title'=>'name','content'))->select();
执行的SQL相当于:
SELECT id,title as name,content FROM table
如果你希望直接使用:
$Model->field('id,title as name,content')->select();
可能会得到错误的结果。
对于一些更复杂的字段要求,数组的优势则更加明显,例如:
$Model->field(array('id','concat(name,'-',id)'=>'truename','LEFT(title,7)'=>'sub_title'))->select();
执行的SQL相当于:
SELECT id,concat(name,'-',id) as truename,LEFT(title,7) as sub_title FROM table
想必大家都明白了,对于需要在field中使用SQL函数的情况,数组方式可以很好的解决。
是不是field方法就这么点作用了呢?如果你这么认为,那就太低估ThinkPHP的field方法了,ThinkPHP考虑的细节远比你想象的要周到。
先看下面的情况,如果有一个表有非常多的字段,而且有两个需求,首先要求需要获取所有的字段,这个也许很简单,因为不调用field方法或者直接使用空的field方法都能做到,事实上,的确如此:
$Model->select(); $Model->field()->select(); $Model->field('*')->select();
上面三个用法是等效的,都相当于执行SQL:
SELECT * FROM table
但是这并不是我说的获取所有字段,我希望显式的调用所有字段(对于对性能要求比较高的系统,这个要求并不过分,起码是一个比较好的习惯),那么OK,仍然很简单,下面的用法可以完成预期的作用:
$Model->field(true)->select();
fied(true)的用法会显式的获取数据表的所有字段列表,哪怕你的数据表有100个字段。
第二个需求是我希望获取排除content字段(文本字段的值非常耗内存)之外的所有字段值,我们就可以使用field方法的排除功能,例如下面的方式就可以实现所说的功能:
$Model->field('content',true)->select();
要排除更多的字段也可以:
$Model->field('user_id,content',true)->select(); //或者用 $Model->field(array('user_id','content'),true)->select();
2、用于写入
除了查询操作之外,field方法还有一个非常重要的安全功能--字段合法性检测(注意:该功能3.1版本开始才能支持)。field方法结合create方法使用就可以完成表单提交的字段合法性检测,如果我们在表单提交的处理方法中使用了:
$Model->field('title,email,content')->create();
即表示表单中的合法字段只有title,email和content字段,无论用户通过什么手段更改或者添加了浏览器的提交字段,都会直接屏蔽。因为,其他的所有字段我们都不希望由用户提交来决定,你可以通过自动完成功能定义额外的字段写入。

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