step 2 with basic crud implemented

app/templates/items/form.html

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+{% extends "base.html" %}
+
+{% block content %}
+<div class="page-header">
+    <div>
+        <h1>{{ page_title }}</h1>
+        <p class="muted">所属箱子：<a href="/boxes/{{ box.id }}">{{ box.name }}</a></p>
+    </div>
+    <a href="/boxes/{{ box.id }}">返回箱子</a>
+</div>
+
+<form method="post" action="{{ form_action }}" class="stack">
+    <label>
+        名称
+        <input type="text" name="name" value="{{ item.name if item else '' }}" required>
+    </label>
+    <label>
+        数量
+        <input type="number" name="quantity" min="0" value="{{ item.quantity if item and item.quantity is not none else '' }}">
+    </label>
+    <label class="checkbox-row">
+        <input type="checkbox" name="is_container" {% if item and item.is_container %}checked{% endif %}>
+        这个物品本身是一个小容器
+    </label>
+    <label>
+        备注
+        <textarea name="note" rows="4">{{ item.note if item and item.note else '' }}</textarea>
+    </label>
+    <button type="submit">{{ submit_label }}</button>
+</form>
+{% endblock %}

app/templates/items/show.html

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+{% extends "base.html" %}
+
+{% block content %}
+<div class="page-header">
+    <div>
+        <h1>{{ item.name }}</h1>
+        <p class="muted">位于箱子 <a href="/boxes/{{ item.box.id }}">{{ item.box.name }}</a> 中</p>
+    </div>
+    <div class="actions">
+        <a href="/boxes/{{ item.box.id }}">返回箱子</a>
+        <a href="/items/{{ item.id }}/edit">编辑物品</a>
+    </div>
+</div>
+
+<section class="card">
+    <p><strong>是否容器：</strong> {{ "是" if item.is_container else "否" }}</p>
+    <p><strong>数量：</strong> {{ item.quantity if item.quantity is not none else '-' }}</p>
+    <p><strong>备注：</strong> {{ item.note or '-' }}</p>
+    <div class="actions">
+        <form method="post" action="/items/{{ item.id }}/delete">
+            <button type="submit" class="link-button">删除物品</button>
+        </form>
+    </div>
+</section>
+
+{% if item.is_container %}
+<section class="stack">
+    <div class="page-header">
+        <h2>子物品</h2>
+        <a class="button" href="/items/{{ item.id }}/subitems/new">添加子物品</a>
+    </div>
+    {% if item.subitems %}
+        {% for subitem in item.subitems %}
+        <article class="card">
+            <h3>{{ subitem.name }}</h3>
+            {% if subitem.quantity is not none %}<p><strong>数量：</strong> {{ subitem.quantity }}</p>{% endif %}
+            {% if subitem.note %}<p><strong>备注：</strong> {{ subitem.note }}</p>{% endif %}
+            <div class="actions">
+                <a href="/subitems/{{ subitem.id }}/edit">编辑</a>
+                <form method="post" action="/subitems/{{ subitem.id }}/delete">
+                    <button type="submit" class="link-button">删除</button>
+                </form>
+            </div>
+        </article>
+        {% endfor %}
+    {% else %}
+    <section class="card">
+        <p>还没有子物品。</p>
+    </section>
+    {% endif %}
+</section>
+{% else %}
+<section class="card">
+    <p>这个物品不是容器，因此不能包含子物品。</p>
+</section>
+{% endif %}
+{% endblock %}