132 lines
6.8 KiB
HTML
132 lines
6.8 KiB
HTML
<!DOCTYPE html><html lang="zh-CN"><head><meta charset="utf-8"><meta name="X-UA-Compatible" content="IE=edge"><title> Django Manager Method · MarkDown</title><meta name="description" content="Django Manager Method - Ching"><meta name="viewport" content="width=device-width, initial-scale=1"><link rel="short icon" href="/favicon.png"><link rel="stylesheet" href="/css/apollo.css"><link rel="stylesheet" href="https://fonts.googleapis.com/css?family=Source+Sans+Pro:400,600" type="text/css"><style><!-- hexo-inject:begin --><!-- hexo-inject:end -->mjx-container[jax="SVG"] {
|
||
direction: ltr;
|
||
}
|
||
|
||
mjx-container[jax="SVG"] > svg {
|
||
overflow: visible;
|
||
}
|
||
|
||
mjx-container[jax="SVG"] > svg a {
|
||
fill: blue;
|
||
stroke: blue;
|
||
}
|
||
|
||
mjx-container[jax="SVG"][display="true"] {
|
||
display: block;
|
||
text-align: center;
|
||
margin: 1em 0;
|
||
}
|
||
|
||
mjx-container[jax="SVG"][justify="left"] {
|
||
text-align: left;
|
||
}
|
||
|
||
mjx-container[jax="SVG"][justify="right"] {
|
||
text-align: right;
|
||
}
|
||
|
||
g[data-mml-node="merror"] > g {
|
||
fill: red;
|
||
stroke: red;
|
||
}
|
||
|
||
g[data-mml-node="merror"] > rect[data-background] {
|
||
fill: yellow;
|
||
stroke: none;
|
||
}
|
||
|
||
g[data-mml-node="mtable"] > line[data-line] {
|
||
stroke-width: 70px;
|
||
fill: none;
|
||
}
|
||
|
||
g[data-mml-node="mtable"] > rect[data-frame] {
|
||
stroke-width: 70px;
|
||
fill: none;
|
||
}
|
||
|
||
g[data-mml-node="mtable"] > .mjx-dashed {
|
||
stroke-dasharray: 140;
|
||
}
|
||
|
||
g[data-mml-node="mtable"] > .mjx-dotted {
|
||
stroke-linecap: round;
|
||
stroke-dasharray: 0,140;
|
||
}
|
||
|
||
g[data-mml-node="mtable"] > svg {
|
||
overflow: visible;
|
||
}
|
||
|
||
[jax="SVG"] mjx-tool {
|
||
display: inline-block;
|
||
position: relative;
|
||
width: 0;
|
||
height: 0;
|
||
}
|
||
|
||
[jax="SVG"] mjx-tool > mjx-tip {
|
||
position: absolute;
|
||
top: 0;
|
||
left: 0;
|
||
}
|
||
|
||
mjx-tool > mjx-tip {
|
||
display: inline-block;
|
||
padding: .2em;
|
||
border: 1px solid #888;
|
||
font-size: 70%;
|
||
background-color: #F8F8F8;
|
||
color: black;
|
||
box-shadow: 2px 2px 5px #AAAAAA;
|
||
}
|
||
|
||
g[data-mml-node="maction"][data-toggle] {
|
||
cursor: pointer;
|
||
}
|
||
|
||
mjx-status {
|
||
display: block;
|
||
position: fixed;
|
||
left: 1em;
|
||
bottom: 1em;
|
||
min-width: 25%;
|
||
padding: .2em .4em;
|
||
border: 1px solid #888;
|
||
font-size: 90%;
|
||
background-color: #F8F8F8;
|
||
color: black;
|
||
}
|
||
|
||
foreignObject[data-mjx-xml] {
|
||
font-family: initial;
|
||
line-height: normal;
|
||
overflow: visible;
|
||
}
|
||
|
||
.MathJax path {
|
||
stroke-width: 3;
|
||
}
|
||
|
||
mjx-container {
|
||
overflow: auto hidden;
|
||
}
|
||
|
||
mjx-container + br {
|
||
display: none;
|
||
}
|
||
</style><!-- hexo-inject:begin --><!-- hexo-inject:end --></head><body><header><a href="/" class="logo-link"><img src="/logo.png"></a><ul class="nav nav-list"><li class="nav-list-item"><a href="/" target="_self" class="nav-list-link">ALL</a></li><li class="nav-list-item"><a href="/categories/leetcode/" target="_self" class="nav-list-link">LEETCODE</a></li><li class="nav-list-item"><a href="https://bearmiebear.blogspot.com" target="_blank" class="nav-list-link">BEAR</a></li><li class="nav-list-item"><a href="/atom.xml" target="_self" class="nav-list-link">RSS</a></li></ul></header><section class="container"><div class="post"><article class="post-block"><h1 class="post-title">Django Manager Method</h1><div class="post-meta"><div class="post-time">2016年4月25日</div></div><div class="post-content"><h4 id="Django_Manager"><a href="#Django_Manager" class="headerlink" title="Django Manager"></a>Django Manager</h4><p>Django 里会为每一个 model 生成一个 Manager，默认名字为 objects，一般情况下对 model 进行的处理都是通过 model.objects.XXX( ) 来进行的。其实是调用了 model 的 manager 的方法，而 manager 之中的方法是 QuerySet 方法的代理，QuerySet 方法是对数据库操作的封装。</p>
|
||
<!-- hexo-inject:begin --><!-- hexo-inject:end --><p>eg.</p>
|
||
<figure class="highlight python"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">from</span> django.db <span class="keyword">import</span> models</span><br><span class="line"></span><br><span class="line"><span class="class"><span class="keyword">class</span> <span class="title">Person</span><span class="params">(models.Model)</span>:</span></span><br><span class="line"> ...</span><br><span class="line"> people = models.Manager()</span><br></pre></td></tr></table></figure>
|
||
<p>上面这个 model，<code>Person.objects</code>会产生一个<code>AttributeError</code>，但是<code>Person.people</code>就可以正常操作。因为默认的 manager 已经变成 people，objects 这个 manager 没有重新声明，不起作用。</p>
|
||
<h4 id="u81EA_u5B9A_u4E49_Manager"><a href="#u81EA_u5B9A_u4E49_Manager" class="headerlink" title="自定义 Manager"></a>自定义 Manager</h4><p>通常需要自定义 manager 的情况有两点:</p>
|
||
<ol>
|
||
<li>需要修改/扩展 Django 的 manager 方法</li>
|
||
<li>需要修改返回的 QuerySet</li>
|
||
</ol>
|
||
<h4 id="u9ED8_u8BA4_Manager"><a href="#u9ED8_u8BA4_Manager" class="headerlink" title="默认 Manager"></a>默认 Manager</h4><p>如果使用自定义的 manager 需要注意的是，Django 将 model 中定义的第一个 manager 认为是默认 manager，而且 Django 框架中会用到默认 manager。</p>
|
||
<p>笨方法是使用自定义 manager 的时候，对于 model 依然提供 objects 这个默认 manager，并放在第一个。</p>
|
||
<p>eg.</p>
|
||
<figure class="highlight python"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br></pre></td><td class="code"><pre><span class="line"><span class="class"><span class="keyword">class</span> <span class="title">Book</span><span class="params">(models.Model)</span>:</span></span><br><span class="line"> title = models.CharField(max_length=<span class="number">100</span>)</span><br><span class="line"> author = models.CharField(max_length=<span class="number">50</span>)</span><br><span class="line"> </span><br><span class="line"> objects = models.Manager() <span class="comment"># default manager</span></span><br><span class="line"> custom_objects = CustomBOokManager() <span class="comment"># custom manager</span></span><br></pre></td></tr></table></figure>
|
||
<p><a href="http://blog.csdn.net/sicofield/article/details/49283751" target="_blank" rel="noopener">source</a></p>
|
||
</div></article></div></section><footer><div class="paginator"><a href="/2016/05/04/Tastypie/" class="prev">PRVE</a><a href="/2016/02/16/Flask-Day-2/" class="next">NEXT</a></div><div class="copyright"><p>© 2016 - 2020 <a href="http://blog.tunpok.com">Ching</a>, unless otherwise noted.</p></div></footer><script src="https://cdn.bootcss.com/mathjax/2.5.3/MathJax.js?config=TeX-AMS-MML_HTMLorMML"></script><!-- hexo-inject:begin --><!-- hexo-inject:end --></body></html> |