Mysql迁移到TiDB双写数据库兜底方案详解

settings.py中新增配置

# Dev Database settings
DATABASES = {
    'default': {
        'ENGINE': 'django.db.backends.mysql',
        'NAME': 'name',
        'USER': 'root',
        'PASSWord': '123456',
        'HOST': 'db',
    },
    'replica': {
        'ENGINE': 'django.db.backends.mysql',
        'NAME': 'name',
        'USER': 'root',
        'PASSWORD': '123456',
        'HOST': 'db',
    },
    'bak': {
        'ENGINE': 'django.db.backends.mysql',
        'NAME': 'name',
        'USER': 'root',
        'PASSWORD': '123456',
        'HOST': 'db',
    },
}
# 多重写入数据库配置
MULTI_WRITE_DB = "bak"

import copy
import logging
import traceback
from django.db import models, transaction, router
from django.db.models.deletion import Collector
from django.db.models import sql
from django.db.models.sql.constants import CURSOR
from jcdp.settings import MULTI_WRITE_DB, DATABASES
multi_write_db = MULTI_WRITE_DB
# 重写QuerySet
class BaseQuerySet(models.QuerySet):
    def create(self, **kwargs):
        return super().create(**kwargs)
    def update(self, **kwargs):
        try:
            rows = super().update(**kwargs)
            if multi_write_db in DATABASES:
                self._for_write = True
                query = self.query.chain(sql.UpdateQuery)
                query.add_update_values(kwargs)
                with transaction.mark_for_rollback_on_error(using=multi_write_db):
                    query.get_compiler(multi_write_db).execute_sql(CURSOR)
        except Exception:
            logging.error(traceback.fORMat_exc())
            raise
        return rows
    def delete(self):
        try:
            deleted, _rows_count = super().delete()
            if multi_write_db in DATABASES:
                del_query = self._chain()
                del_query._for_write = True
                del_query.query.select_for_update = False
                del_query.query.select_related = False
                collector = Collector(using=multi_write_db)
                collector.collect(del_query)
                collector.delete()
        except Exception:
            logging.error(traceback.format_exc())
            raise
        return deleted, _rows_count
    def raw(self, raw_query, params=None, translations=None, using=None):
        try:
            qs = super().raw(raw_query, params=params, translations=translations, using=using)
            if multi_write_db in DATABASES:
                super().raw(raw_query, params=params, translations=translations, using=multi_write_db)
        except Exception:
            logging.error(traceback.format_exc())
            raise
        return qs
    def bulk_create(self, objs, batch_size=None, ignore_conflicts=False):
        try:
            for obj in objs:
                obj.save()
        except Exception:
            logging.error(traceback.format_exc())
            raise
        # objs = super().bulk_create(objs, batch_size=batch_size, ignore_conflicts=ignore_conflicts)
        # if multi_write_db in DATABASES:
        #     self._db = multi_write_db
        #     super().bulk_create(objs, batch_size=batch_size, ignore_conflicts=ignore_conflicts)
        return objs
    def bulk_update(self, objs, fields, batch_size=None):
        try:
            super().bulk_update(objs, fields, batch_size=batch_size)
            if multi_write_db in DATABASES:
                self._db = multi_write_db
                super().bulk_update(objs, fields, batch_size=batch_size)
        except Exception:
            logging.error(traceback.format_exc())
            raise
class BaseManager(models.Manager):
    _queryset_class = BaseQuerySet
class BaseModel(models.Model):
    objects = BaseManager()
    class Meta:
        abstract = True
    def delete(
            self, using=None, *args, **kwargs
    ):
        try:
            instance = copy.deepcopy(self)
            super().delete(using=using, *args, **kwargs)
            if multi_write_db in DATABASES:
                super(BaseModel, instance).delete(using=multi_write_db, *args, **kwargs)
        except Exception:
            logging.error(traceback.format_exc())
            raise
    def save_base(self, raw=False, force_insert=False,
                  force_update=False, using=None, update_fields=None):
        try:
            using = using or router.db_for_write(self.__class__, instance=self)
            assert not (force_insert and (force_update or update_fields))
            assert update_fields is None or update_fields
            cls = self.__class__
            # Skip proxies, but keep the origin as the proxy model.
            if cls._meta.proxy:
                cls = cls._meta.concrete_model
            meta = cls._meta
            # A transaction isn't needed if one query is issued.
            if meta.parents:
                context_manager = transaction.atomic(using=using, savepoint=False)
            else:
                context_manager = transaction.mark_for_rollback_on_error(using=using)
            with context_manager:
                parent_inserted = False
                if not raw:
                    parent_inserted = self._save_parents(cls, using, update_fields)
                self._save_table(
                    raw, cls, force_insert or parent_inserted,
                    force_update, using, update_fields,
                )
            if multi_write_db in DATABASES:
                super().save_base(raw=raw,
                                  force_insert=raw,
                                  force_update=force_update,
                                  using=multi_write_db,
                                  update_fields=update_fields)
            # Store the database on which the object was saved
            self._state.db = using
            # Once saved, this is no longer a to-be-added instance.
            self._state.adding = False
        except Exception:
            logging.error(traceback.format_exc())
            raise

class DirectoryStructure(BaseModel):
    """
    目录结构
    """
    view = models.CharField(max_length=128, db_index=True)  # 视图名称 eg：部门视图 项目视图
    sub_view = models.CharField(max_length=128, unique=True, db_index=True)  # 子视图名称
    sub_view_num = models.IntegerField()  # 子视图顺序号