最佳方法查询 Django Rest Framework 中的数据库是什么？

huangapple
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英文:

What is the best method to query db in django rest framework

问题

我有models.py

  1. class Category(MPTTModel):
  2.     # 几个字段
  4. class Brand(models.Model):
  5.     # 几个字段
  7. class Attribute(models.Model):
  8.    # 几个字段
  10. class AttributeValue(models.Model):
  11.    attributes = models.ForeignKey(Attribute, # 其他条件)
  12.    # 几个字段
  14. class Product(models.Model):
  15.    category = models.ForeignKey(Category, # 其他条件)
  16.    brand = models.ForeignKey(Brand, # 其他条件)
  17.    attributes = models.ManyToManyField(Attribute, # 其他条件)
  18.    # 其他字段
  20. class ProductImages(models.Model):
  21.    product = models.ForeignKey(Product, # 其他条件)

在views.py，我有

  1. class ProductAPIView(generics.GenericAPIView):
  3.     serializer_class = ProductSerializer
  4.     queryset = Product.objects.all()

serializers.py

  1. class ProductSerializer(serializers.ModelSerializer):
  2.     brand = serializers.SlugRelatedField(queryset=Brand.objects.all())
  3.     category = serializers.SlugRelatedField(queryset=Category.objects.all())
  4.     attributes = AttributeSerializer(many=True, read_only=True)
  5.     product_images = ProductImageSerializer(many=True, read_only=True)

我得到的JSON响应如下

  1. {
  2.     "brand": ...,
  3.     "category": ...,
  4.     "attributes": [
  5.         { "attribute_values": [...] },
  6.         { "attribute_values": [...] }
  7.     ],
  8.     "product_images": [{...}, {...}]
  9. }

我了解到select_related和prefetch_related可以优化外键字段和多对多字段的数据库查询。

我将查询集更改为queryset = Product.objects.select_related('category', 'brand').all()

如何在ProductAPIView中更改查询集以包括attributes、product_images和attribute_values字段，并提高性能？

英文:

I have models.py

  1. class Category(MPTTModel):
  2.     # few fields
  4. class Brand(models.Model):
  5.     # few fields
  7. class Attribute(models.Model):
  8.    # few fields
  10. class AttributeValue(models.Model):
  11.    attributes = models.ForeignKey(Attribute, # other conditions)
  12.    # few fields
  14. class Product(models.Model):
  15.    category = models.ForeignKey(Category, # other conditions)
  16.    brand = models.ForeignKey(Brand, # other conditions)
  17.    attributes = models.ManyToManyField(Attribute, # other conditions)
  18.    # few other fields
  20. class ProductImages(models.Model):
  21.    product = models.ForeignKey(Product, # other conditions)

In views.py, I have

  1. class ProductAPIView(generics.GenericAPIView):
  3.     serializer_class = ProductSerializer
  4.     queryset = Product.objects.all()

serializers.py

  1. class ProductSerializer(serializers.ModelSerializer):
  2.     brand = serializers.SlugRelatedField(queryset = Brand.objects.all())
  3.     category = serializers.SlugRelatedField(queryset = Category.objects.all())
  4.     attributes = AttributeSerializer(many = True, read_only = True)
  5.     product_images = ProductImageSerializer(many = True, read_only = True)

I'm getting my json response like this

  1. {
  2.     "brand": ...,
  3.     "category": ...,
  4.     "attributes": [
  5.         { "attribute_values": [...] },
  6.         { "attribute_values": [...] }
  7.     ],
  8.     "product_images": [{...}, {...}]
  9. }

I came across select_related and prefetch_related which will optimise the db queries on foreign key fields and many-to-many fields.

I changed the queryset to queryset = Product.objects.select_related('category', 'brand').all()

How can i change the queryset in ProductAPIView to include the attributes, product_images and attribute_values fields also and improve the performance here ?

答案1

得分: 1

以下是您要翻译的部分：

"for the first part of your question you can take a look at Prefetch and this question.

for debugging purposes I always use this decorator:

  1. from django.db import connection, reset_queries
  2. import time
  3. import functools
  6. def query_debugger(func):
  8.     @functools.wraps(func)
  9.     def inner_func(*args, **kwargs):
  11.         reset_queries()
  12.         
  13.         start_queries = len(connection.queries)
  15.         start = time.perf_counter()
  16.         result = func(*args, **kwargs)
  17.         end = time.perf_counter()
  19.         end_queries = len(connection.queries)
  21.         print(f"Function : {func.__name__}")
  22.         print(connection.queries)
  23.         print(f"Number of Queries : {end_queries - start_queries}")
  24.         print(f"Finished in : {(end - start):.2f}s")
  25.         return result
  27.     return inner_func

And use it like this:

  1. @query_debugger
  2. def get(self, request, *args, **kwargs):
  3.    pass
  4. ```"
  6. <details>
  7. <summary>英文:</summary>
  9. for the first part of your question you can take a look at [Prefetch](https://docs.djangoproject.com/en/4.2/ref/models/querysets/#django.db.models.Prefetch)
  10. and this [question](https://stackoverflow.com/questions/54569384/django-chaining-prefetch-related-and-select-related?answertab=scoredesc#tab-top).
  12. for debugging purposes I always use this decorator:

from django.db import connection, reset_queries
import time
import functools

def query_debugger(func):

  1. @functools.wraps(func)
  2. def inner_func(*args, **kwargs):
  4.     reset_queries()
  5.     
  6.     start_queries = len(connection.queries)
  8.     start = time.perf_counter()
  9.     result = func(*args, **kwargs)
  10.     end = time.perf_counter()
  12.     end_queries = len(connection.queries)
  14.     print(f&quot;Function : {func.__name__}&quot;)
  15.     print(connection.queries)
  16.     print(f&quot;Number of Queries : {end_queries - start_queries}&quot;)
  17.     print(f&quot;Finished in : {(end - start):.2f}s&quot;)
  18.     return result
  20. return inner_func
  1. And use it like this:

@query_debugger
def get(self, request, *args, **kwargs):
pass

  3. </details>
  7. # 答案2
  8. **得分**: 1
  10. 你可以链式使用 `select_related` 和 `prefetch_related`：
  12. ```python
  13. class ProductAPIView(generics.GenericAPIView):
  15.     serializer_class = ProductSerializer
  16.     queryset = Product.objects.select_related('category', 'brand').prefetch_related("attributes")

或者覆盖 get_queryset 函数：

  1. class ProductAPIView(generics.GenericAPIView):
  3.     serializer_class = ProductSerializer
  4.     
  5.     def get_queryset(self):
  6.         qs = super().get_queryset()
  7.         return qs.select_related('category', 'brand').prefetch_related("attributes")

你可以使用 Prefetch 类来指定在 prefetch_related() 中使用的查询集，并以这种方式与 select_related() 结合使用：

英文:

you can chain select_realted & prefetch_related

  1. class ProductAPIView(generics.GenericAPIView):
  3.     serializer_class = ProductSerializer
  4.     queryset = Product.objects.select_related(&#39;category&#39;, &#39;brand&#39;).prefetch_related(&quot;attributes&quot;)

or override get_queryset function

  1. class ProductAPIView(generics.GenericAPIView):
  3.     serializer_class = ProductSerializer
  4.     
  5.     def get_queryset(self):
  6.         qs =  super().get_queryset()
  7.         return qs.select_related(&#39;category&#39;, &#39;brand&#39;).prefetch_related(&quot;attributes&quot;)

You can use the Prefetch class to specify the queryset that is used in prefetch_related() and this way combine it with select_related():

huangapple
  • 本文由 发表于 2023年5月13日 18:45:29
  • 转载请务必保留本文链接：https://go.coder-hub.com/76242311.html
  • django
  • django-prefetch-related
  • django-rest-framework
  • django-select-related
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