SQLAlchemy:从连接多个表中获取单个对象 [英] SQLAlchemy: Getting a single object from joining multiple tables

问题描述

考虑两个表的经典设置 - user 和 api_key，由 SQLAlchemy 对象表示为:

Consider a classic setting of two tables - user and api_key, represented by SQLAlchemy objects as:

class User(Base):
    __tablename__ = 'user'
    user_id = Column(String)
    user_name = Column(String)
    vioozer_api_key = Column(String, ForeignKey("api_key.api_key"))

class ApiKey(Base):
    __tablename__ = 'api_key'    
    api_key = Column(String(37), primary_key=True)

为清楚起见，省略了其他字段.

Other fields omitted for clarity.

假设我想获取特定用户 ID 的用户名和 api 密钥:

Suppose that I want to get the user name and the api key for a specific user id:

user, api_key = database.db_session.query(User, ApiKey)\
    .join(ApiKey, User.vioozer_api_key==ApiKey.api_key)\
    .filter(User.user_id=='user_00000000000000000000000000000000').first()

我得到两个对象 - user 和 api_key，我可以从中获取 user.name 和 api_key.api_key.

I get two objects - user and api_key, from which I can fetch user.name and api_key.api_key.

我想用一个函数包装这个调用，该函数将返回一个对象，其字段将是 user 字段和 api_key 字段的联合 -SQL join 以同样的方式返回一个表，其中两个表的列都被连接起来.有没有办法自动获取一个对象，其字段是两个表的字段的并集?

I would like to wrap this call with a function, which would return a single objects whose fields would be the union of the user fields and the api_key fields - the same way a SQL join returns a table with the columns of both tables being joined. Is there a wayo to automatically get a object whose fields are the union of the fields of both tables?

我可以为每个 Join 操作定义一个 mapper class，但是我想知道是否可以自动完成映射.

I can define a mapper class for each Join operation, but I wonder if the mapping could be done automatically.

推荐答案

不是查询对象，而是查询字段列表，在这种情况下 SQLAlchemy 返回 KeyedTuple，提供 KeyedTuple._asdict() 方法可用于返回任意字典:

Instead of querying objects, query for list of fields instead, in which case SQLAlchemy returns instances of KeyedTuple, which offers KeyedTuple._asdict() method you can use to return arbitrary dictionary:

def my_function(user_id):
    row =  database.db_session.query(User.name, ApiKey.api_key)\
        .join(ApiKey, User.vioozer_api_key==ApiKey.api_key)\
        .filter(User.user_id==user_id).first()
    return row._asdict()

my_data = my_function('user_00000000000000000000000000000000')

但是对于您的特定查询，您甚至不需要加入 ApiKey，因为 api_key 字段存在于 User 表中:

But for your particular query, you do not need even to join on ApiKey as the api_key field is present on the User table:

row = database.db_session.query(User.name, User.api_key)\
    .filter(User.user_id==user_id).first()

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