sqlalchemy 同时连接多个数据库。完成flask_sqlalchemy的__bind_key__功能

本文链接：https://blog.youkuaiyun.com/weixin_42068117/article/details/83857355

本文介绍了如何使用SQLAlchemy在Flask应用中同时连接并操作多个数据库，包括通过`__bind_key__`实现数据库绑定，以及通过`engine.binds`配置不同数据库连接。示例代码展示了具体的配置和使用方法。

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https://github.com/zzzeek/sqlalchemy/blob/master/lib/sqlalchemy/sql/schema.py

 """Symbol indicating that a :class:`.Table` or :class:`.Sequence`
    should have 'None' for its schema, even if the parent
    :class:`.MetaData` has specified a schema.
    .. versionadded:: 1.0.14
 """

def _get_table_key(name, schema):
    if schema is None:
        return name
    else:
        return schema + "." + name

这一段代码显示的是我们给定的schema会拼接数据库的名字。大家应该可以理解是数据库.表名这样就不会有数据库的限制。这一段属于示例给大家理解的，如果只想知道怎么用，直接看本文最后的代码示例就可以了。

class Table(DialectKWArgs, SchemaItem, TableClause):

"""
 The :class:`.Table` object constructs a unique instance of itself based
    on its name and optional schema name within the given
    :class:`.MetaData` object. Calling the :class:`.Table`
    constructor with the same name and same :class:`.MetaData` argument
    a second time will return the *same* :class:`.Table` object - in this way
    the :class:`.Table` constructor acts as a registry function.

  :param schema: The schema name for this table, which is required if
        the table resides in a schema other than the default selected schema
        for the engine's database connection.  Defaults to ``None``.
        If the owning :class:`.MetaData` of this :class:`.Table` specifies
        its own :paramref:`.MetaData.schema` parameter, then that schema