在Django中动态地过滤查询集的实现
作者：前端小工
本文主要介绍了Django中动态地过滤查询集的实现，文中通过示例代码介绍的非常详细，具有一定的参考价值，感兴趣的小伙伴们可以参考一下
简介
要建立一个允许过滤和分页的列表页，你必须让一些独立的东西一起工作。Django的对象关系映射器（ORM）和内置的分页类使开发者在不了解如何处理数据库和SQL的情况下，也能轻松地提高工作效率。在本指南中，你将学习如何使用AJAX动态地过滤查询集。
在本文的例子中，我采用了Spotify上按国家划分的前50首歌的数据集。你也可以从这里下载同样的数据集。像往常一样，本指南中使用的代码可以在GitHub上找到。你可以在本指南的结尾处找到这个链接。
开始使用
要开始，请像这样启动一个新的Django项目。
django-admin startproject my_proj
然后，创建一个示例应用程序。
cd my_proj python manage.py startapp my_app
更新settings.py 。
INSTALLED_APPS += [
'my_app'
]这里是你在指南中要遵循的目录结构。
├── db.sqlite3 ├── manage.py ├── my_app/ │ ├── __init__.py │ ├── admin.py │ ├── apps.py │ ├── migrations/ │ ├── models.py │ ├── templates/ │ │ ├── base.html │ │ └── index.html │ ├── tests.py │ └── views.py ├── my_proj/ │ ├── __init__.py │ ├── asgi.py │ ├── settings.py │ ├── urls.py │ └── wsgi.py └── top50contry.csv └── requirements.txt
数据准备
在跳转到实际代码之前，我们首先需要将所有数据推送到数据库。
我已经创建了一个名为TopSongPoularity 的基本模型来存储数据集的必要信息。
下面是my_app 的models.py 。
## my_app/models.py
from django.db import models
class TopSongPoularity(models.Model):
title = models.CharField(max_length = 220)
artist = models.CharField(max_length = 220)
top_genre = models.CharField(max_length = 220)
year = models.IntegerField()
pop = models.IntegerField()
duration = models.IntegerField()
country = models.CharField(max_length = 100)
def __str__(self):
return self.title现在你已经创建了模型，用下面的方法将其迁移到数据库中。
python manage.py makemigrations python manage.py migrate
接下来，我们要把所有的CSV数据推送到数据库中，所以我们要用shell来执行一个脚本。
python manage.py shell
在shell中运行下面的脚本，将CSV数据推送到数据库中。
#Django Shell
import csv
from datetime import datetime
from my_app.models import TopSongPoularity
with open('top50contry.csv', 'r') as fin:
reader = csv.reader(fin)
headers = next(reader, None)
for row in reader:
obj = {
"title": row[1],
"artist": row[2],
"top_genre": row[3],
"year": int(row[4]),
"pop": int(row[15]),
"duration": int(row[12]),
"country": row[16]
}
TopSongPoularity.objects.create(**obj)创建视图
接下来，让我们来编写视图。ListTopSongs 是一个基于类的视图（CBV），它继承了View 类。在该类的get() 方法中，它接受查询参数并相应地过滤QuerySet。在QuerySet被过滤后，它再调用get_paginated_context() ，以获得序列化格式的分页数据。
getCountries() 是一个基于函数的视图（FBV），它为数据库中所有独特的国家返回JSON输出。
#my_app/views.py
import json
from django.core.paginator import Paginator
from django.core.serializers import serialize
from django.http import JsonResponse
from django.shortcuts import render
from django.views import View
from .models import TopSongPoularity
def index(request):
return render(request, "index.html", {})
class ListTopSongs(View):
# set default page limit as 10
page_limit = 10 # default
'''
Helper method to get the pagination context
out of queryset of given page number with limit.
Args:
queryset: Filtered queryset object
page: a number representing the page number
limit: the result count, per page.
Returns the JSON of queryset for the given page,
with pagination meta info.
'''
def get_paginated_context(self, queryset, page, limit):
if not page: page = 1 # if no page provided, set 1
# if limit specified, set the page limit
if limit:
self.page_limit = limit
# instantiate the paginator object with queryset and page limit
paginator = Paginator(queryset, self.page_limit)
# get the page object
page_obj = paginator.get_page(page)
# serialize the objects to json
serialized_page = serialize("json", page_obj.object_list)
# get only required fields from the serialized_page json.
serialized_page = [obj["fields"] for obj in json.loads(serialized_page)]
# return the context.
return {
"data": serialized_page,
"pagination": {
"page": page,
"limit": limit,
"has_next": page_obj.has_next(),
"has_prev": page_obj.has_previous(),
"total": queryset.count()
}
}
'''
GET method for this View.
'''
def get(self, request, *args, **kwargs):
# fetch the query params
page = request.GET.get('page')
limit = request.GET.get('limit')
country = request.GET.get('country')
start = request.GET.get('start')
end = request.GET.get('end')
sort_by = request.GET.get('sort_by')
# get all results from DB.
queryset = TopSongPoularity.objects.all()
'''filter the queryset object based on query params'''
# 1. on basis of country
if country and country != "all":
queryset = queryset.filter(country=country)
# 2. On basis of date (start and end date)
if start and end:
if start != "0" and end != "0":
queryset = queryset.filter(
year__gte = start,
year__lte = end
)
# 3. Sorting the filtered queryset
if sort_by and sort_by != "0":
queryset = queryset.order_by(sort_by)
# return the serialized output by
# calling method 'get_paginated_context'
to_return = self.get_paginated_context(queryset, page, limit)
return JsonResponse(to_return, status = 200)
def getCountries(request):
# get Countries from the database
# excluding null and blank values
if request.method == "GET" and request.is_ajax():
country = TopSongPoularity.objects.all().\
values_list('country').distinct()
country = [c[0] for c in list(country)]
return JsonResponse({
"country": country,
}, status = 200)创建URL
现在，让我们对视图进行路由。
#my_proj/urls.py
from django.urls import path
from my_app.views import ListTopSongs, index, getCountries
urlpatterns = [
path('api/get/top_songs', ListTopSongs.as_view()),
path('api/get/countries', getCountries, name = "get_countries"),
path('', index)
]创建模板
现在后端代码已经完成，让我们转到前端。
我使用了一个基本模板(base.html)，包括Bootstrap和jQuery库。
<!--templates/base.html-->
<!--doctype HTML-->
<html>
<head>
<meta charset="utf-8" />
<meta http-equiv="X-UA-Compatible" content="IE=edge">
<meta property="og:locale" content="en_US" />
<meta charset="utf-8" />
<meta http-equiv="X-UA-Compatible" content="IE=edge">
<meta name="viewport" content="width=device-width, initial-scale=1">
<title>Log rocket</title>
<!-- css cdn includes -->
<link rel="stylesheet" href = "https://stackpath.bootstrapcdn.com/bootstrap/4.5.2/css/bootstrap.min.css">
{% block style %}
{% endblock style %}
</head>
<body>
{% block content %}
{% endblock %}
<script src="https://ajax.googleapis.com/ajax/libs/jquery/3.1.1/jquery.min.js"></script>
<script src="https://stackpath.bootstrapcdn.com/bootstrap/4.5.2/js/bootstrap.min.js"></script>
{% block javascript %}
{% endblock javascript %}
</body>
</html>现在，让我们创建index.html ，显示带有过滤器的表格。这个模板文件继承了base.html ，并创建了一个带有标题和空主体的表格。最后，它还包含两个 "下一步 "和 "上一步 "的按钮。
index.html 的其余部分，即JavaScript部分，将在下面解释。
<!--templates/index.html-->
{% extends 'base.html' %}
{% block content %}
<section>
<div class="container-fluid">
<div class="row">
<div class="col-sm-2 col-2">
<div class="form-group">
<label for="country">Country</label>
<select class="form-control" id="countries" url={% url 'get_countries' %}>
</select>
</div>
</div>
<div class="col-sm-2 col-2">
<div class="form-group">
<label for="year">Year</label>
<select class="form-control" id="year">
<option value="0" start=0 end=0>All years</option>
<option value="1" start=2019 end=2020>2019-2020</option>
<option value="2" start=2018 end=2019>2018-2019</option>
<option value="3" start=2016 end=2018>2016-2018</option>
<option value="4" start=2010 end=2016>2010-2016</option>
<option value="5" start=1900 end=2010>1900-2010</option>
</select>
</div>
</div>
<div class="col-sm-2 col-2">
<div class="form-group">
<label for="sort">Sort By</label>
<select class="form-control" id="sort">
<option value="0">No option selected</option>
<option value="duration">Duration</option>
<option value="pop">Pop</option>
<option value="year">Year</option>
</select>
</div>
</div>
</div>
</div>
</section>
<section>
<div class="container">
<div class="row justify-content-center table-responsive">
<div id="result-count" class="text-right">
<span class='font-weight-bold'></span> results found.
</div>
<div id="page-count" class="text-right">Page:
<span class='font-weight-bold'></span>
</div>
<table class="table table-light table-bordered table-hover" id="hero_table" data-toggle="table">
<thead class="thead-dark">
<tr>
<th data-field="title">Title</th>
<th data-field="country">Country</th>
<th data-field="top_genre">Top Genre</th>
<th data-field="artist">Artist</th>
<th data-field="duration">Duration</th>
<th data-field="pop">Pop</th>
<th data-field="year">Year</th>
</tr>
</thead>
<tbody id="table_body">
</tbody>
</table>
</div>
<div class="row justify-content-center">
<nav aria-label="navigation">
<ul class="pagination">
<li class="page-item">
<button class="btn btn-primary page-link" id = "previous">Previous</button>
</li>
<li class="page-item pull-right">
<button class="btn btn-primary page-link" id="next">Next</button>
</li>
</ul>
</nav>
</div>
</div>
</section>
{% endblock content %}创建客户端脚本
本指南的最后一部分是使用AJAX连接前端和后端。请参考下面代码片断中提到的注释。
<!---templates/index.html--->
{% block javascript %}
<script>
// maintaining the state of each variable.
var current_page = 1; // maintains the current page
var page_limit = 10; // the limit of results shown on page.
var sort_by = ""; // maintains the select option for sort_by
var country = ""; // maintains the select option for country
var start_year = ""; // maintains the select option for start_yr
var end_year = ""; // maintains the select option for end_yr
function get_list_url(page) {
// returns the consructed url with query params.
return `api/get/top_songs?page=${page}&limit=${page_limit}&country=${country}&sort_by=${sort_by}&start=${start_year}&end=${end_year}`;
}
function getCountries() {
// call the ajax and populates the country select options
$.ajax({
method: 'GET',
url: $("#countries").attr("url"),
success: function (response) {
countries_option = "<option value='all' selected>All Countries</option>";
$.each(response["country"], function (a, b) {
countries_option += "<option>" + b + "</option>"
});
$("#countries").html(countries_option)
},
error: function (response) {
console.log(response)
}
});
}
// On select change of the country select, call the getAPIData
$("#countries").on("change", function (e) {
current_page = 1;
country = this.value
getAPIData(get_list_url(current_page));
});
// On select change of the year select, call the getAPIData
$("#year").on("change", function (e) {
current_page = 1;
start_year = $(this).find(':selected').attr("start");
end_year = $(this).find(':selected').attr("end");
getAPIData(get_list_url(current_page));
})
// On select change of the sort select, call the getAPIData with sortby.
$("#sort").on("change", function (e) {
current_page = 1;
sort_by = this.value
getAPIData(get_list_url(current_page));
})
// Helper method that popluates the html table with next and prev
// url, and current page number.
function putTableData(response) {
// creating table row for each response and
// pushing to the html cntent of table body of table_body table
let row;
$("#table_body").html("");
if (response["data"].length > 0) {
$.each(response["data"], function (a, b) {
row = "<tr> <td>" + b.title + "</td>" +
"<td>" + b.country + "</td>" +
"<td>" + b.top_genre + "</td>" +
"<td>" + b.artist + "</td>" +
"<td>" + b.duration + "</td>" +
"<td>" + b.pop + "</td>" +
"<td>" + b.year + "</td>" +
$("#table_body").append(row);
});
}
else{
// if there is no results found!
$("#table_body").html("No results found.");
}
if (response.pagination.has_prev) {
// sets the previous page url.
$("#previous").attr("data-url", get_list_url(current_page - 1));
$("#previous").attr("disabled", false);
} else {
// if there is no prev page available, disable the btn.
$("#previous").attr("disabled", true);
}
if (response.pagination.has_next) {
// sets the next page url.
$("#next").attr("data-url", get_list_url(current_page + 1));
$("#next").attr("disabled", false);
} else {
// if there is no next page available, disable the btn.
$("#next").attr("disabled", true)
}
}
// On click of next/prev button, call the getAPIData with the given url.
$(".page-link").click(function (e) {
e.preventDefault();
let url = $(this).attr("data-url");
getAPIData(url);
})
// Main method which calls AJAX to get the data from backend.
function getAPIData(url) {
$.ajax({
method: 'GET',
url: url,
success: function (response) {
current_page = parseInt(response.pagination.page)
putTableData(response);
// put the total result count.
$("#result-count span").html(response.pagination.total)
$("#page-count span").html(response.pagination.page)
},
error: function (response) {
$("#hero_table").hide();
}
});
}
//on page load, call this two methods.
getAPIData(get_list_url(current_page));
getCountries()
</script>
{% endblock javascript %}结语
在本指南中，你已经学会了如何使用AJAX以及如何与后端进行异步通信。过滤表格数据是一个常见的处理场景，我希望本指南能让你更好地了解如何处理过滤数据。
如果你愿意，你也可以使用REST框架，如Django REST框架来保持简单。
如果你在遵循本指南的过程中遇到任何问题，你可以随时查看我的Github仓库来查看整个项目。
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