※ 引述《left (881 forever)》之铭言： : 各位大大 : 在djangobook上有一段说明为啥要data model的地方看不太懂 : 有人可以帮忙解说一下吗？ : 这里的introspection是指？ : 感谢 : http://djangobook.com/django-models/ : Introspection requires overhead and is imperfect. : In order to provide convenient data-access APIs, Django needs to know : the database layout somehow, and there are two ways of accomplishing this. : The first way would be to explicitly describe the data in Python, : and the second way would be to introspect the database at runtime to : determine the data models.This second way seems cleaner, because : the metadata about your tables lives in only one place, but it introduces : a few problems. First, introspecting a database at runtime obviously : requires overhead. If the framework had to introspect the database : each time it processed a request, or even only when the Web server : was initialized, this would incur an unacceptable level of overhead. : (While some believe that level of overhead is acceptable, : Django’s developers aim to trim as much framework overhead as possible.) : Second, some databases, notably older versions of MySQL, : do not store sufficient metadata for accurate and complete introspection. 这段就是在说web framework要能够跟资料库拿资料的话， 需要知道资料库的table, schema等资讯 然後web framework有两种方法可以知道这种资讯: 1. 写在程式里定义好资料库要有的表跟栏位 2. 在程式跑起来的时候去检视(Introspect)资料库既有的栏位 然後django采取的是第一种做法 因为第二种做法会增加不必要的复杂度 django实际上的作法就是在models.py里定义好资料的结构 然後下migrate的指令就可以生成database里的table 资料结构有变动时也是先改models.py的内容 再靠makemigrations跟migrate的指令来完成 这样能确保程式码跟资料库结构的一致性，避免一些奇怪的问题产生 --

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