python – scrapy – 处理多种类型的项目 – 多个和相关的Django

发布时间：2020-12-20 13:08:27 所属栏目：Python 来源：网络整理

导读：我有以下Django模型.我不确定在使用scrapy管道将蜘蛛扫描到Django中的数据库时,保存这些相互关联对象的最佳方法是什么.似乎scrapy管道只是为了处理一种“种类”的物品 models.py class Parent(models.Model): field1 = CharField()class ParentX(models.Mode

我有以下Django模型.我不确定在使用scrapy管道将蜘蛛扫描到Django中的数据库时,保存这些相互关联对象的最佳方法是什么.似乎scrapy管道只是为了处理一种“种类”的物品

models.py

class Parent(models.Model):
    field1 = CharField()


class ParentX(models.Model):
    field2 = CharField()
    parent = models.OneToOneField(Parent,related_name = 'extra_properties')


class Child(models.Model):
    field3 = CharField()
    parent = models.ForeignKey(Parent,related_name='childs')

items.py

# uses DjangoItem https://github.com/scrapy-plugins/scrapy-djangoitem

class ParentItem(DjangoItem):
    django_model = Parent

class ParentXItem(DjangoItem):
    django_model = ParentX

class ChildItem(DjangoItem):
    django_model = Child

spiders.py

class MySpider(scrapy.Spider):
    name = "myspider"
    allowed_domains = ["abc.com"]
    start_urls = [
        "http://www.example.com",# this page has ids of several Parent objects whose full details are in their individual pages

    ]

    def parse(self,response):
        parent_object_ids = [] #list from scraping the ids of the parent objects

        for parent_id in parent_object_ids:
            url = "http://www.example.com/%s" % parent_id
            yield scrapy.Request(url,callback=self.parse_detail)

    def parse_detail(self,response):
        p = ParentItem()
        px = ParentXItem()
        c = ChildItem()



        # populate p,px and c1,c2 with various data from the response.body

        yield p
        yield px
        yield c1
        yield c2 ... etc c3,c4

pipelines.py – 不知道该怎么做

class ScrapytestPipeline(object):
    def process_item(self,item,spider):


        # This is where typically storage to database happens
        # Now,I dont know whether the item is a ParentItem or ParentXItem or ChildItem

        # Ideally,I want to first create the Parent obj and then ParentX obj (and point p.extra_properties = px),and then child objects 
        # c1.parent = p,c2.parent = p

        # But I am not sure how to have pipeline do this in a sequential way from any order of items received

解决方法

如果你想按顺序进行操作,如果你将一个项目存储在另一个项目中,我会支持,一个depakage – 它在管道中,它可能会起作用.

我认为在保存db之前更容易关联对象.

在spiders.py中,当你“使用来自response.body的各种数据填充p,px和c1,c2”时,你可以填充从对象数据构造的“假”主键.

然后你可以保存数据并在模型中更新 – 如果已经只在一个管道中被删除：

class ItemPersistencePipeline(object):
    def process_item(self,spider):
        try:
             item_model = item_to_model(item)
        except TypeError:
            return item   
        model,created = get_or_create(item_model)
        try:
            update_model(model,item_model)
        except Exception,e:
            return e
        return item

当然方法：

def item_to_model(item):
    model_class = getattr(item,'django_model')
    if not model_class:
        raise TypeError("Item is not a `DjangoItem` or is misconfigured")   
    return item.instance   

def get_or_create(model):
    model_class = type(model)
    created = False
    try:
        #We have no unique identifier at the moment
        #use the model.primary for now
        obj = model_class.objects.get(primary=model.primary)
    except model_class.DoesNotExist:
        created = True
        obj = model  # DjangoItem created a model for us.

    return (obj,created)

from django.forms.models import model_to_dict

def update_model(destination,source,commit=True):
    pk = destination.pk

    source_dict = model_to_dict(source)
    for (key,value) in source_dict.items():
        setattr(destination,key,value)

    setattr(destination,'pk',pk)

    if commit:
        destination.save()

    return destination

来自：How to update DjangoItem in Scrapy

您还应该在django模型中定义字段“primary”以搜索是否已经在新项目中进行了搜索

models.py

class Parent(models.Model):
    field1 = CharField()   
    #primary_key=True
    primary = models.CharField(max_length=80)
class ParentX(models.Model):
    field2 = CharField()
    parent = models.OneToOneField(Parent,related_name = 'extra_properties')
    primary = models.CharField(max_length=80) 
class Child(models.Model):
    field3 = CharField()
    parent = models.ForeignKey(Parent,related_name='childs')
    primary = models.CharField(max_length=80)

（编辑：李大同）

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