SQLAlchemy 中的 Model.query 和 session.query(Model) 有什么区别? [英] What's the difference between Model.query and session.query(Model) in SQLAlchemy?

问题描述

我是 SQLAlchemy 的初学者，发现查询可以通过 2 种方法完成:

I'm a beginner in SQLAlchemy and found query can be done in 2 method:

方法一:

DBSession = scoped_session(sessionmaker())
class _Base(object):
    query = DBSession.query_property()

Base = declarative_base(cls=_Base)

class SomeModel(Base):
    key   = Column(Unicode, primary_key=True)
    value = Column(Unicode)

# When querying
result = SomeModel.query.filter(...)

方法二

DBSession = scoped_session(sessionmaker())
Base = declarative_base()

class SomeModel(Base):
    key   = Column(Unicode, primary_key=True)
    value = Column(Unicode)

# When querying
session = DBSession()
result = session.query(SomeModel).filter(...)

它们之间有什么区别吗?

Is there any difference between them?

推荐答案

在上面的代码中，没有什么区别.这是因为，在第一个示例的第 3 行:

In the code above, there is no difference. This is because, in line 3 of the first example:

• query 属性明确绑定到 DBSession
• 没有自定义的 Query 对象传递给 query_property

• the query property is explicitly bound to DBSession
• there is no custom Query object passed to query_property

正如@petr-viktorin 在此处的答案中指出的那样，在定义模型之前必须有可用的会话在第一个示例中，这可能会出现问题，具体取决于您的应用程序的结构.

As @petr-viktorin points out in the answer here, there must be a session available before you define your model in the first example, which might be problematic depending on the structure of your application.

但是，如果您需要一个自定义查询来自动向所有查询添加额外的查询参数，那么只有第一个示例允许这样做.从 sqlalchemy.orm.query.Query 继承的自定义查询类可以作为参数传递给 query_property.这个问题展示了这种模式的一个例子.

If, however, you need a custom query that adds additional query parameters automatically to all queries, then only the first example will allow that. A custom query class that inherits from sqlalchemy.orm.query.Query can be passed as an argument to query_property. This question shows an example of that pattern.

即使模型对象上定义了自定义查询属性，在使用 session.query 进行查询时也不会使用该属性，如第二个示例的最后一行.这意味着如果您需要自定义查询类，则类似于第一个示例的唯一选项.

Even if a model object has a custom query property defined on it, that property is not used when querying with session.query, as in the last line in the second example. This means something like the first example the only option if you need a custom query class.

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