摘要：前言一般來說解決連接多個庫的最簡單的方式是新建兩個或多個相互沒有關聯配置不同的來連接這樣的話正常配置就行不用特殊配置如果這樣解決的話也就不用看下面的配置了不可以加上如下的五種方式都是可以的這個配置很關鍵很關鍵這個配置很關鍵用戶工

一般來說,解決sqlalchemy 連接多個庫的最簡單的方式是新建兩個或多個db.session 相互沒有關聯,modle配置不同的db.session來連接,這樣的話,relationship正常配置就行,不用特殊配置.如果這樣解決的話,也就不用看下面的配置了

# -*- coding:utf-8 -*-

import flask
from flask_sqlalchemy import SQLAlchemy  # Flask-SQLAlchemy 2.3.2
from datetime import datetime
from sqlalchemy.orm import backref, foreign  # SQLAlchemy 1.3.1

app = flask.Flask(__name__)
app.config["DEBUG"] = True
app.config["SQLALCHEMY_BINDS"] = {
    "read_db": "mysql://reader:test@127.0.0.1:3306/test?charset=utf8",
    "write_db": "mysql://writer:test@127.0.0.2:3306/test?charset=utf8"
}

app.config["SQLALCHEMY_TRACK_MODIFICATIONS"] = False
app.config["SQLALCHEMY_ECHO"] = False
db = SQLAlchemy(app)


class RDriver(db.Model):
    __bind_key__ = "read_db"
    __tablename__ = "driver"
    # __table_args__ = {"schema": "test"} # 不可以加上

    id = db.Column(db.Integer, primary_key=True, autoincrement=True)
    fk_user_id = db.Column(db.Integer, db.ForeignKey("user.id"))
    driver_name = db.Column(db.String(7))
    create_time = db.Column(db.TIMESTAMP, default=datetime.now)


class RUser(db.Model):
    __bind_key__ = "read_db"
    __tablename__ = "user"
    # __table_args__ = {"schema": "test"}

    id = db.Column(db.Integer, primary_key=True, autoincrement=True)
    user_name = db.Column(db.String(32), index=True, unique=True)
    user_password = db.Column(db.String(32))
    create_time = db.Column(db.TIMESTAMP, default=datetime.now)
    update_time = db.Column(db.TIMESTAMP, default=datetime.now)
    # 如下的五種方式都是可以的
    # driver_fk = db.relationship("RDriver", foreign_keys="RDriver.fk_user_id")
    # driver_fk = db.relationship("RDriver", primaryjoin=lambda: RDriver.fk_user_id == RUser.id, viewonly=True)
    # driver_fk = db.relationship("RDriver", primaryjoin=RDriver.fk_user_id == id)
    fk_driver = db.relationship("RDriver", primaryjoin="RDriver.fk_user_id == RUser.id")
    # driver_fk = db.relationship("RDriver", backref=db.backref("user", lazy=True),
    #                             primaryjoin=lambda: RDriver.fk_user_id == RUser.id, viewonly=True)


class WDriver(db.Model):
    __bind_key__ = "write_db"
    __tablename__ = "driver"
    __table_args__ = {"schema": "test", "extend_existing": True} # 這個配置很關鍵

    id = db.Column(db.Integer, primary_key=True, autoincrement=True)
    fk_user_id = db.Column(db.Integer, db.ForeignKey("test.user.id"))   # test.user.id很關鍵
    plate = db.Column(db.String(7))
    create_at = db.Column(db.TIMESTAMP, default=datetime.now)


class WUser(db.Model):
    __bind_key__ = "write_db"
    __tablename__ = "user"
    __table_args__ = {"schema": "test", "extend_existing": True}    # 這個配置很關鍵

    id = db.Column(db.Integer, primary_key=True, autoincrement=True)
    hash = db.Column(db.String(256), nullable=False)
    user_no = db.Column(db.String(32), index=True, unique=True)  # 用戶工號
    create_time = db.Column(db.TIMESTAMP, default=datetime.now)
    update_time = db.Column(db.TIMESTAMP, default=datetime.now)
    # 以下五種方式都是可以的
    # fk_driver = db.relationship("WDriver", foreign_keys="WDriver.fk_user_id", uselist=False)
    # fk_driver = db.relationship("WDriver", primaryjoin=lambda: WDriver.fk_user_id == WUser.id)
    fk_driver = db.relationship("WDriver", primaryjoin=WDriver.fk_user_id == id)
    # fk_driver = db.relationship("WDriver", primaryjoin="WDriver.fk_user_id == WUser.id")
    # fk_driver = db.relationship("WDriver", backref=db.backref("test.user", lazy=True),
    #                             primaryjoin=lambda: WDriver.fk_user_id == WUser.id)



r_user_obj = RUser.query.filter_by().first()
print("r_user_obj:", r_user_obj)
print("r_user_obj.driver_fk:", r_user_obj.fk_driver)
w_user_obj = WUser.query.filter_by(id=2188).first()
print("w_user_obj:", w_user_obj)
print("w_user_obj.driver_fk:", w_user_obj.fk_driver)

* https://docs.sqlalchemy.org/en/13/orm/relationship_api.html # 值得細看
* https://www.osgeo.cn/sqlalchemy/orm/relationship_api.html # 同上,中文
* https://www.cnblogs.com/srd945/p/9851227.html
* extend_existing: (False)當表已經存在于元數據中時，如果元數據中存在與column_list中的列同名的列，column_list中同名的列會替換掉元數據中已經有的列
* useexisting已被廢棄, 新版本使用extend_existing

關系配置參數真的很多,如下,很容易就會出錯,需要多讀讀官方文檔,還有就是建立modle時候盡量簡潔,風格統一,不要在數據庫層建立外鍵.

sqlalchemy.orm.relationship(argument, secondary=None, primaryjoin=None, secondaryjoin=None, foreign_keys=None,
uselist=None, order_by=False, backref=None, back_populates=None, post_update=False, cascade=False, extension=None,
viewonly=False, lazy="select", collection_class=None, passive_deletes=False, passive_updates=True, remote_side=None,
enable_typechecks=True, join_depth=None, comparator_factory=None, single_parent=False, innerjoin=False,
distinct_target_key=None, doc=None, active_history=False, cascade_backrefs=True, load_on_pending=False,
bake_queries=True, _local_remote_pairs=None, query_class=None, info=None, omit_join=None)