Django 不通过外键实现多表关联查询

Django不通过外键实现多表关联查询

by:授客 QQ：1033553122

测试环境

Win 10

 

Python 3.5.4

 

Django-2.0.13.tar.gz

需求

不通过外键，使用django orm语法实现多个表之间的关联查询,类似如下sql的查询效果：

SELECT tb_project_version.*, tb_sprint.name, tb_project.name

FROM tb_project_version

JOIN tb_sprint ON tb_sprint.id=tb_project_version.sprint_id

JOIN tb_project ON tb_project.id=tb_project_version.project_id

数据表Model设计

class Sprint(models.Model):

id = models.AutoField(primary_key=True, verbose_name='自增id')

name = models.CharField(max_length=50, verbose_name='迭代名称')

...略

class Meta:

db_table = 'tb_sprint'

        verbose_name = '产品迭代表'

        verbose_name_plural = verbose_name

class Project(models.Model):

id = models.AutoField(primary_key=True, verbose_name='自增id')

name = models.CharField(max_length=50, verbose_name='项目名称')

...略

class Meta:

db_table = 'tb_project'

        verbose_name = '项目表'

        verbose_name_plural = verbose_name

 

class ProjectVersion(models.Model):

id = models.AutoField(primary_key=True, verbose_name='自增id')

name = models.CharField(max_length=50, verbose_name='版本名称')

project_id = models.IntegerField(verbose_name='关联的项目ID')

sprint_id = models.IntegerField(verbose_name='关联的迭代ID')

...略

class Meta:

db_table = 'tb_project_version'

        verbose_name = '项目版本表'

        verbose_name_plural = verbose_name

实现方法1-通过extra api函数实现

如下，带背景色部分的内容为核心

serializers.py

#!/usr/bin/env python

# -*- coding:utf-8 -*-

 

from rest_framework import serializers

from backend.models import ProjectVersion

 

# ProjectVersion model 序列化器

class ProjectVersionSerializer(serializers.ModelSerializer):

project = serializers.CharField(required=True)

sprint = serializers.CharField(required=True)

class Meta:

model = ProjectVersion

fields = '__all__'

read_only_fields = ['project', 'sprint']

说明：如上，如果使用了django rest framework序列化，则需要为其序列化器添加model中不存在的字段，否则序列化后还是看不到对应的目标字段

project_version_views.py

#!/usr/bin/env python

# -*- coding:utf-8 -*-

 

__author__ = '授客'

 

from rest_framework.views import APIView

from rest_framework.response import Response

from rest_framework import status

from backend.models import ProjectVersion

from backend.serializers import ProjectVersionSerializer

class ProjectVersionListAPIView(APIView):

'''

    项目视图-版本管理

    '''

    # 查询列表数据

    def get(self, request, format=None):

result = {}

try:

params =  request.GET

page_size = int(params.get('pageSize'))

page_no = int(params.get('pageNo'))

name = params.get('name')

project_id = params.get('projectId')

sort = params.get('sort')

if sort:

sort_list = sort.split(',')

else:

sort_list = ['-id']

startIndex = (page_no - 1) * page_size

endIndex = startIndex + page_size

filters = {'is_delete':0}

if name:

filters['name__startswith'] = name

if project_id:

filters['project_id'] = project_id

projectVersions = ProjectVersion.objects.filter(**filters).extra(

select={'project': 'SELECT tb_project.name FROM tb_project WHERE tb_project.id = tb_project_version.project_id',

'sprint':'SELECT tb_sprint.name FROM tb_sprint WHERE tb_sprint.id = tb_project_version.sprint_id'},

)

rows = projectVersions.order_by(*sort_list)[startIndex:endIndex]

rows = ProjectVersionSerializer(rows, many=True).data

total = projectVersions.count()

result['msg'] =  '获取成功'

            result['success'] =  True

            result['data'] = {}

result['data']['rows'] = rows

result['data']['total'] = total

return Response(result, status.HTTP_200_OK)

except Exception as e:

result['msg'] =  '%s' % e

result['success'] =  False

            return Response(result, status.HTTP_500_INTERNAL_SERVER_ERROR)

说明：

projectVersions.order_by(*sort_list)[startIndex:endIndex]

等价于

SELECT (SELECT tb_project.name FROM tb_project WHERE tb_project.id = tb_project_version.project_id) AS `project`,

(SELECT tb_sprint.name FROM tb_sprint WHERE tb_sprint.id = tb_project_version.sprint_id) AS `sprint`,

`tb_project_version`.`id`,

`tb_project_version`.`name`,

`tb_project_version`.`project_id`,

`tb_project_version`.`sprint_id`,

...略

FROM `tb_project_version`

WHERE `tb_project_version`.`is_delete` = 0

ORDER BY `tb_project`.`id` DESC LIMIT 10 # 假设startIndex=0, endIndex=10

projectVersions.count()

等价于

SELECT COUNT(*) AS `__count` FROM `tb_project_version`

WHERE `tb_project_version`.`is_delete` = 0

上述查询代码的另一种实现

projectVersions =  Project.objects.filter(**filters).extra(

select={'project:'tb_project.name',

'sprint':' tb_sprint.name',

tables=['tb_project', 'tb_sprint'],

where=['tb_project.id=tb_project_version.project_id', 'tb_sprint.id = tb_project_version.sprint_id']

)

rows = projectVersions.order_by(*sort_list)[startIndex:endIndex]

rows = ProjectVersionSerializer(rows, many=True).data

total = projectVersions.count()

projectVersions.order_by(*sort_list)[startIndex:endIndex]

等价于

SELECT (tb_project.name) AS `project`,

(tb_sprint.name) AS `sprint`,

`tb_project_version`.`id`,

`tb_project_version`.`name`,

`tb_project_version`.`project_id`,

`tb_project_version`.`sprint_id`,

...略

FROM `tb_project_version`

WHERE `tb_project_version`.`is_delete` = 0 AND (tb_project.id=tb_project_version.project_id) AND (tb_sprint.id = tb_project_version.sprint_id)

ORDER BY `tb_project`.`id` DESC LIMIT 10 # 假设startIndex=0, endIndex=10

projectVersions.count()

等价于

SELECT COUNT(*) AS `__count` FROM `tb_project_version` , `tb_project` , `tb_sprint` WHERE `tb_project_version`.`is_delete` = 0 AND (tb_project.id=tb_project_version.project_id) AND (tb_sprint.id = tb_project_version.sprint_id)

实现方法2-通过django rest framework实现

serializers.py

#!/usr/bin/env python

# -*- coding:utf-8 -*-

 

from rest_framework import serializers

from backend.models import ProjectVersion

from backend.models import Sprint

from backend.models import Project

# ProjectVersion model 序列化器

class ProjectVersionSerializer(serializers.ModelSerializer):

project = serializers.SerializerMethodField()

    sprint = serializers.SerializerMethodField()

def get_sprint(self, obj):

"""

        :param obj: 当前ProjectVersion的实例

        """

        current_project_version = obj

sprint = Sprint.objects.filter(id=current_project_version.sprint_id).first()

if sprint:

return sprint.name

else:

return '--'

 

def get_project(self, obj):

"""

        :param obj: 当前ProjectVersion的实例

        """

        current_project_version = obj

project = Project.objects.filter(id=current_project_version.project_id).first()

if project:

return project.name

else:

return '--'

 

    class Meta:

model = ProjectVersion

fields = '__all__'

read_only_fields = ['project', 'sprint']

 

project_version_views.py

#!/usr/bin/env python

# -*- coding:utf-8 -*-

 

__author__ = '授客'

 

from rest_framework.views import APIView

from rest_framework.response import Response

from rest_framework import status

from backend.models import ProjectVersion

from backend.serializers import ProjectVersionSerializer

class ProjectVersionListAPIView(APIView):

'''

    项目视图-版本管理

    '''

    # 查询列表数据

    def get(self, request, format=None):

result = {}

try:

params =  request.GET

page_size = int(params.get('pageSize'))

page_no = int(params.get('pageNo'))

name = params.get('name')

project_id = params.get('projectId')

sort = params.get('sort')

if sort:

sort_list = sort.split(',')

else:

sort_list = ['-id']

startIndex = (page_no - 1) * page_size

endIndex = startIndex + page_size

filters = {'is_delete':0}

if name:

filters['name__startswith'] = name

if project_id:

filters['project_id'] = project_id

rows = ProjectVersion.objects.filter(**filters).order_by(*sort_list)[startIndex:endIndex]

rows = ProjectVersionSerializer(rows, many=True).data

total = ProjectVersion.objects.filter(**filters).count()

result['msg'] =  '获取成功'

            result['success'] =  True

            result['data'] = {}

result['data']['rows'] = rows

result['data']['total'] = total

return Response(result, status.HTTP_200_OK)

except Exception as e:

result['msg'] =  '%s' % e

result['success'] =  False

            return Response(result, status.HTTP_500_INTERNAL_SERVER_ERROR)

方法3-通过raw函数执行原生sql

以下是项目中的一个实例，和本文上述内容没有任何关联，关键部分背景已着色，笔者偷懒，不做过多解释了，简单说下下面这段代码对用途：

主要是实现类似以下查询，获取指定分页对数据以及满足条件的记录记录总数。

SELECT tb_project.*, project_name_associated, project_id_associated, platform FROM tb_project

LEFT JOIN tb_project_associated ON tb_project.id=tb_project_associated.project_id

ORDER BY id DESC

LIMIT 0,10

from rest_framework.views import APIView

from rest_framework.response import Response

from rest_framework import status

from backend.models import Project

from backend.serializers import ProjectSerializer

import logging

logger = logging.getLogger('mylogger')

class ProjectListAPIView(APIView):

'''

    项目视图-项目管理-项目列表

    '''

 

    # 查询列表数据

    def get(self, request, format=None):

result = {}

try:

params =  request.GET

page_size = int(params.get('pageSize'))

page_no = int(params.get('pageNo'))

name = params.get('name')

project_status = params.get('status')

sort = params.get('sort')

order_by = 'id desc'

            if sort:

order_by = sort

            startIndex = (page_no - 1) * page_size

            where = 'WHERE tb_project.is_delete=0 '

            filters = {'is_delete':0}

if name:

filters['name__startswith'] = name

where += 'AND locate("%s", name) ' % name

if project_status:

       where += "AND status='%s'" % project_status

sql = 'SELECT tb_project.id, COUNT(1) AS count FROM tb_project LEFT JOIN tb_project_associated ON tb_project.id=tb_project_associated.project_id '

            query_rows = Project.objects.raw(sql)

total = query_rows[0].__dict__.get('count') if query_rows else 0

sql =  'SELECT tb_project.*,project_name_associated, project_id_associated, platform FROM tb_project LEFT JOIN tb_project_associated ON tb_project.id=tb_project_associated.project_id ' \

'%s ORDER BY %s ' \

'LIMIT %s,%s ' % (where,order_by, startIndex, page_size)

query_rows = Project.objects.raw(sql)

rows = []

for item in query_rows:

item.__dict__.pop('_state')

item.__dict__['create_time'] = item.__dict__['create_time'].strftime('%Y-%m-%d %H:%M:%S')

item.__dict__['update_time'] = item.__dict__['update_time'].strftime('%Y-%m-%d %H:%M:%S')

item.__dict__['begin_time'] = item.__dict__['begin_time'].strftime('%Y-%m-%d')

item.__dict__['end_time'] = item.__dict__['end_time'].strftime('%Y-%m-%d')

rows.append(item.__dict__)

            result['msg'] =  '获取成功'

            result['success'] =  True

            result['data'] = {}

result['data']['rows'] = rows

result['data']['total'] = total

return Response(result, status.HTTP_200_OK)

except Exception as e:

result['msg'] =  '%s' % e

result['success'] =  False

            return Response(result, status.HTTP_500_INTERNAL_SERVER_ERROR)

参考链接

https://docs.djangoproject.com/en/1.11/ref/models/querysets/#django.db.models.query.QuerySet.extra

https://www.jianshu.com/p/973971880da7