通用查询
1、公共函数：
def generic_query(model, filter_kwargs=None, order_by=None, limit=None, aggregate=None, annotate=None):"""通用的 Django ORM 查询函数。:param model: Django 模型类:param filter_kwargs: 过滤条件字典:param order_by: 字符串或字符串列表，用于指定排序字段:param limit: 返回结果的数量限制:param aggregate: 聚合函数字典，例如 {'total': Sum('price')}:param annotate: 注解字段字典，例如 {'item_count': Count('items')}:return: 查询结果"""queryset = model.objects.all()# 应用过滤条件if filter_kwargs:queryset = queryset.filter(**filter_kwargs)# 应用排序if order_by:if isinstance(order_by, str):order_by = [order_by]queryset = queryset.order_by(*order_by)# 应用聚合if aggregate:return queryset.aggregate(**aggregate)# 应用注解if annotate:queryset = queryset.annotate(**annotate)# 应用结果数量限制if limit is not None:queryset = queryset[:limit]try:# 尝试获取单个对象result = queryset.get()except (ObjectDoesNotExist, MultipleObjectsReturned):# 如果没有找到对象或找到多个对象，则返回整个查询集result = querysetreturn result2、示例
# 有两个模型 Book 和 Author，其中 Book 有一个外键关联到 Author# app/model.py
from django.db import modelsclass Author(models.Model):name = models.CharField(max_length=100)class Book(models.Model):title = models.CharField(max_length=200)author = models.ForeignKey(Author, on_delete=models.CASCADE)price = models.DecimalField(max_digits=5, decimal_places=2)publication_date = models.DateField()# =========================
# app/view.py# 获取所有书籍
books = generic_query(Book)
print(books)# 根据价格过滤书籍
cheap_books = generic_query(Book, filter_kwargs={'price__lt': 10.00})
print(cheap_books)# 按作者名称排序书籍
sorted_books = generic_query(Book, order_by=['author__name'])
print(sorted_books)# 获取前 5 本书
top_five_books = generic_query(Book, limit=5)
print(top_five_books)# 计算所有书籍的平均价格
average_price = generic_query(Book, aggregate={'avg_price': Avg('price')})
print(average_price)# 统计每个作者的书籍数量
books_per_author = generic_query(Book, annotate={'book_count': Count('author')})
print(books_per_author)通用创建
1、公共函数：
from django.core.exceptions import ValidationErrordef generic_create(model, **kwargs):"""通用的 Django ORM 创建函数。:param model: Django 模型类:param kwargs: 要创建的对象的属性值:return: 创建的对象实例"""try:# 创建并保存对象obj = model(**kwargs)obj.full_clean() # 验证数据是否符合模型的约束obj.save()return objexcept ValidationError as e:# 处理验证错误raise ValueError(f"Validation error: {e}")except Exception as e:# 处理其他异常raise ValueError(f"An error occurred: {e}")2、示例
# 有两个模型 Book 和 Author，其中 Book 有一个外键关联到 Author
from django.db import modelsclass Author(models.Model):name = models.CharField(max_length=100)class Book(models.Model):title = models.CharField(max_length=200)author = models.ForeignKey(Author, on_delete=models.CASCADE)price = models.DecimalField(max_digits=5, decimal_places=2)publication_date = models.DateField()# =======================# 创建一个新的作者
new_author = generic_create(Author, name="J.K. Rowling")
print(new_author)# 创建一本新书: 先获取或创建一个关联作者, 再创建一本书
author = generic_create(Author, name="George Orwell")
new_book = generic_create(Book, title="1984", author=author, price=15.99, publication_date="1949-06-08")
print(new_book)# 创建一本书并关联已有的作者
# 假设已经有一个作者对象
existing_author = Author.objects.get(name="J.K. Rowling")# 创建一本书并关联已有的作者
new_book = generic_create(Book, title="Harry Potter and the Chamber of Secrets", author=existing_author, price=12.99, publication_date="1998-07-02")
print(new_book)# 处理多对多关系：
# 一个作者并关联多本书
# 创建多个书籍对象
book1 = generic_create(Book, title="Book 1", author=existing_author, price=10.99, publication_date="2020-01-01")
book2 = generic_create(Book, title="Book 2", author=existing_author, price=11.99, publication_date="2020-02-01")
# 获取/创建一个作者并关联多本书
existing_author = Author.objects.get(name="J.K. Rowling")
existing_author.books.add(book1, book2) # 假设 Author 模型中有一个 ManyToManyField 名为 books
print(existing_author)通用更新
def generic_update(model, filter_kwargs, update_fields):"""通用的 Django ORM 修改函数。:param model: Django 模型类:param filter_kwargs: 要修改的对象的过滤条件字典:param update_fields: 要更新的字段及其新值的字典:return: 修改后的对象实例"""try:# 获取对象filter_objs = model.objects.filter(**filter_kwargs)if filter_objs:obj = filter_objs.first()else:raise ObjectDoesNotExist# 更新字段for field, value in update_fields.items():setattr(obj, field, value)# 验证数据是否符合模型的约束obj.full_clean()# 保存对象obj.save()return objexcept ObjectDoesNotExist:raise ValueError(f"Object with filter_kwargs {filter_kwargs} does not exist.")except ValidationError as e:# 处理验证错误raise ValueError(f"Validation error: {e}")except Exception as e:# 处理其他异常raise ValueError(f"An error occurred: {e}")通用删除
def generic_delete(model, filter_kwargs):"""通用的 Django ORM 删除函数。:param model: Django 模型类:param filter_kwargs: 要删除的对象的字典属性值:return: 删除的对象实例（如果成功删除）"""try:# 获取对象# 获取对象filter_objs = model.objects.filter(**filter_kwargs)if filter_objs:obj = filter_objs.first()else:raise ObjectDoesNotExist# 删除对象obj.delete()return objexcept ObjectDoesNotExist:raise ValueError(f"Object with primary filter_kwargs {filter_kwargs} does not exist.")except Exception as e:# 处理其他异常raise ValueError(f"An error occurred: {e}")
