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contains\u eager和joinedload之间的SQLAlchemy差异

sqlalchemy sql python

Igor Komar · 技术社区 · 6 年前

SQLAlchemy的区别是什么 contains_eager 和 joinedload 。我读了 manual 关于contains\u eager,和 manual 关于joinedload。它们都可以用于加载一对多相关行或多对一。

它们正在生成相同的sql:

query = session.query(User).\
    outerjoin(adalias, User.addresses).\
    options(contains_eager(User.addresses, alias=adalias)).all()

...

SELECT
    users.user_id AS users_user_id,
    users.user_name AS users_user_name,
    adalias.address_id AS adalias_address_id,
    adalias.user_id AS adalias_user_id,
    adalias.email_address AS adalias_email_address,
    (...other columns...)
FROM users
LEFT OUTER JOIN email_addresses AS email_addresses_1
ON users.user_id = email_addresses_1.user_id


>>> jack = session.query(User).\
... options(joinedload(User.addresses)).\
... filter_by(name='jack').all()

SELECT
    addresses_1.id AS addresses_1_id,
    addresses_1.email_address AS addresses_1_email_address,
    addresses_1.user_id AS addresses_1_user_id,
    users.id AS users_id, users.name AS users_name,
    users.fullname AS users_fullname,
    users.password AS users_password
FROM users
LEFT OUTER JOIN addresses AS addresses_1
    ON users.id = addresses_1.user_id
WHERE users.name = ?
['jack']

有人能给出更具体的代码示例吗?