在中将默认值设置为Null

Question

from pymodm import connect, fields, MongoModel, EmbeddedMongoModel
from pymongo import IndexModel, ASCENDING, TEXT,client_session
import arrow
from sqlalchemy.log import echo_property
from sqlalchemy.orm import session, sessionmaker
# from .models import *
from scrapy.utils.project import get_project_settings
import arrow
from time import sleep
from sqlalchemy.sql.expression import null

from sqlalchemy.sql.schema import PrimaryKeyConstraint


def db_connect():
    """
    Performs database connection using database settings from settings.py.
    Returns sqlalchemy engine instance
    """
    engine = connect("mongodb://localhost:27017/abcd")
    return engine

now = arrow.get(arrow.now('America/New_York')).datetime

class Live_pr(MongoModel):
    uni_identifier = fields.CharField(required=True,primary_key=True)
    symbol = fields.ListField(required=True)
    #...........
    #..........
    price_dollar = fields.FloatField(blank=True, null=True, default=None) #I want set default Null for this field
    is_new = fields.IntegerField(default=1)
    scrape_timestamp = fields.DateTimeField(default=now)

    class Meta:
        cascade = True

db_connect()

#.....
#scrapy pipeline code
#....

def process_item(self, item, spider):
    prs = Live_pr()

    prs.uni_identifier = item["uni_identifier"]
    prs.symbol = item["symbols"]
    if item["price"]:
        prs.price_dollar = item["price"]
    prs.save()

我只想知道在mongoengine模型中是否存在将默认值设置为Null的方法，“default=None”并不是work.It只会删除整个字段。设置"null=true“会引发此类型错误：

"/home/*******/.local/lib/python3.9/site-packages/pymodm/fields.py"，文件

第89行，在init超级(CharField，self).init(verbose_name=verbose_name，TypeError：init() )中有一个意外的关键字参数'null'

Answer 1

您可以像这样设置默认值：

field2 = fields.CharField(blank=True, null=True, default=None)