Google App Engine: 数据库对象不可迭代
我正在做一个电子商务网站，使用的是Google App Engine和Python。这里是我在数据存储中定义的“产品”实体：
现在，我想根据用户的偏好来筛选一些产品。用户可以通过下拉选项来选择这些偏好。以下是我在'newbooks.html'中的相关代码：
<form method = "post">
<p>Department: </p>
<select name = "branch">
<option></option>
<option>Computers</option>
<option>EXTC</option>
<option>IT</option>
<option>ETRX</option>
<option>MECH</option>
</select>
<br>
<br>
<p>Semester: </p>
<select name = "semester">
<option></option>
<option>1</option>
<option>2</option>
<option>3</option>
<option>4</option>
<option>5</option>
<option>6</option>
<option>7</option>
<option>8</option>
</select>
<br>
<br>
<p>Publications: </p>
<select name = "publications">
<option></option>
<option>Techmax</option>
<option>Nandu</option>
<option>Pearson</option>
<option>Tata McGraw Hill</option>
<option>Technical</option>
</select>
<br>
<br>
<p>Subject: </p>
<select name = "subject">
<option></option>
<option>System Programming and Compiler Construction</option>
<option>Advanced Microprocessors</option>
<option>Microprocessors and Interfacing</option>
<option>Computer Networks</option>
<option>Data Warehouse and Data Mining</option>
</select>
<br><br>
<input type = "submit">
</form>
这是我的Python代码：
class NewBooks(Handler):
def get(self):
self.render("newbooks.html")
def post(self):
branch = self.request.get("branch")
semester = self.request.get("semester")
publications = self.request.get("publications")
subject = self.request.get("subject")
if semester:
yo = int(semester)
if(branch and semester and publications and subject):
disp = Products.all().filter("branch =", branch).filter("publisher =", publications).filter("name =", subject).filter("semester =", yo).get()
self.render("newbooks.html", disp = disp)
elif(branch and semester and publications):
disp = Products.all().filter("branch =", branch).filter("publisher =", publications).filter("semester =", yo).get()
self.render("newbooks.html", disp = disp)
elif(branch and semester and subject):
disp = Products.all().filter("branch =", branch).filter("name =", subject).filter("semester =", yo).get()
self.render("newbooks.html", disp = disp)
elif(branch and publications and subject):
disp = Products.all().filter("branch =", branch).filter("publisher =", publications).filter("name =", subject).get()
self.render("newbooks.html", disp = disp)
elif(semester and publications and subject):
disp = Products.all().filter("publisher =", publications).filter("name =", subject).filter("semester =", yo).get()
self.render("newbooks.html", disp = disp)
elif(branch and semester):
disp = Products.all().filter("branch =", branch).filter("semester =", yo).get()
self.render("newbooks.html", disp = disp)
elif(semester and publications):
disp = Products.all().filter("publisher =", publications).filter("semester =", yo).get()
self.render("newbooks.html", disp = disp)
elif(publications and subject):
disp = Products.all().filter("publisher =", publications).filter("name =", subject).get()
self.render("newbooks.html", disp = disp)
elif(branch and subject):
disp = Products.all().filter("branch =", branch).filter("name =", subject).get()
self.render("newbooks.html", disp = disp)
elif(branch and publications):
disp = Products.all().filter("branch =", branch).filter("publisher =", publications).get()
self.render("newbooks.html", disp = disp)
elif(semester and subject):
disp = Products.all().filter("name =", subject).filter("semester =", yo).get()
self.render("newbooks.html", disp = disp)
elif(branch):
disp = Products.all().filter("branch =", branch).get()
self.render("newbooks.html", disp = disp)
elif(semester):
disp = Products.all().filter("semester =", yo).get()
self.render("newbooks.html", disp = disp)
elif(publications):
disp = Products.all().filter("publisher =", publications).get()
self.render("newbooks.html", disp = disp)
elif(subject):
disp = Products.all().filter("name =", subject).get()
self.render("newbooks.html", disp = disp)
但是，当用户选择并提交他们的筛选条件后，我遇到了以下错误：
TypeError: 'Products' object is not iterable
我的代码有什么问题呢？为什么我数据库中的条目不能被迭代？