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我想将明确的主-主数据库设置与 Flask 和 SQLAlchemy 一起使用，希望 Flask-SQLAlchemy 支持这一点。

我希望能够执行以下代码片段之类的操作，但我不确定 Flask-SQLAlchemy 是否支持它

from flask import Flask
from flask.ext.sqlalchemy import SQLAlchemy

app = Flask(__name__)
SQLALCHEMY_DATABASE_URI = 'default_DB_uri'
SQLALCHEMY_BINDS = { 'master1':'first_master_DB_uri', 'master2': 'second_master_DB_uri' }

app.config['SQLALCHEMY_DATABASE_URI'] = SQLALCHEMY_DATABASE_URI
app.config['SQLALCHEMY_BINDS'] = SQLALCHEMY_BINDS

db = SQLAlchemy(app)

@app.route('/some_endpoint')
def some_endpoint():
    # read some data for the default DB
    readData = db.session.query('select ...')

    m = SomeModel()
    masterSession1 = db.session(bind='master1')
    # persist the data in m into the first master
    masterSession1.add(m)

    masterSession2 = db.session(bind='master2')
    # persist the data into the second master
    masterSession2.add(m)

    return "some return value"

有没有办法使用 Flask-SQLAlchemy 和绑定来实现这一点？我猜 Flask-SQLAlchemy 已经使用绑定处理了多个引擎，但我看不出如何将其用于显式 DB 选择，而不是像这里提到的基于模型的选择：http: //pythonhosted.org/Flask- SQLAlchemy/binds.html

谢谢您的帮助。

4

1 回答 1

1

The code below is what I ended up with to have this functionality.

A few notes:

  • I changed get_table_for_bind to bind all tables without an explicit __bind_key__ to all the binds. This is done in order to be able to call db.create_all() or db.drop_all() and create/drop the tables in all the DBs. In order for this to work and not break the default DB selection, when not specifying a specific bind, get_binds was changed to map the None bind again after the original implementation, to override the Table->Bind mapping.
  • If you don't specify a using_bind everything should work with the default DB.
  • SQLAlchemy mapped objects keep a reference to the session and state so you can't really add the same object to two DBs. I made a copy of the object before adding it in order to persist it in two DBs. Not sure if there is some better way to do this.
  • I haven't fully tested this and this might break some other functionality I'm not using or not aware of.

flask-sqlalchemy overrides:

from flask_sqlalchemy import SQLAlchemy, SignallingSession, get_state
from flask_sqlalchemy._compat import itervalues

class UsingBindSignallingSession(SignallingSession):
    def get_bind(self, mapper=None, clause=None):
        if self._name:
            _eng = get_state(self.app).db.get_engine(self.app,bind=self._name)
            return _eng
        else:
            return super(UsingBindSignallingSession, self).get_bind(mapper, clause)

    _name = None
    def using_bind(self, name):
        self._name = name
        return self

class UsingBindSQLAlchemy(SQLAlchemy):
    def create_session(self, options):
        return UsingBindSignallingSession(self, **options)

    def get_binds(self, app=None):
        retval = super(UsingBindSQLAlchemy, self).get_binds(app)
        # get the binds for None again in order to make sure that it is the default bind for tables
        # without an explicit bind
        bind = None
        engine = self.get_engine(app, bind)
        tables = self.get_tables_for_bind(bind)
        retval.update(dict((table, engine) for table in tables))
        return retval

    def get_tables_for_bind(self, bind=None):
        """Returns a list of all tables relevant for a bind.
        Tables without an explicit __bind_key__ will be bound to all binds.
        """
        result = []
        for table in itervalues(self.Model.metadata.tables):
            # if we don't have an explicit __bind_key__ bind this table to all databases
            if table.info.get('bind_key') == bind or table.info.get('bind_key') == None:
                result.append(table)
        return result

db = UsingBindSQLAlchemy()

Now you can do this:

# This is the default DB
SQLALCHEMY_DATABASE_URI=YOUR_MAIN_DB_URI_CONNECT_STRING
# Master1 and Master2
SQLALCHEMY_BINDS = { 'master1':YOUR_MASTER1_DB_URI_CONNECT_STRING, 'master2':YOUR_MASTER2_DB_URI_CONNECT_STRING }

# Tables without __bind_key__ will be dropped/created on all DBs (default, master1, master2)
db.drop_all()
db.create_all()

s = db.session().using_bind('master1')
s.add(SOME_OBJECT)
s.commit()

s = db.session().using_bind('master2')
s.add(SOME_OBJECT_CLONE) # a clone of the original object, before the first add()
s.commit()

# and the default DB, as always
db.session.add(SOME_OTHER_OBJECT)
db.session.commit()
于 2013-12-02T10:48:23.083 回答