问题：Flask SQLAlchemy查询，指定列名
如何使用模型在查询中指定所需的列（默认情况下会选择所有列）？我知道如何使用sqlalchmey会话：session.query(self.col1)，但是如何使用模型呢？我做不到SomeModel.query()。有办法吗？
How do I specify the column that I want in my query using a model (it selects all columns by default)? I know how to do this with the sqlalchmey session: session.query(self.col1), but how do I do it with with models? I can’t do SomeModel.query(). Is there a way?
回答 0
您可以使用该with_entities()方法来限制要返回结果的列。（文件）
result = SomeModel.query.with_entities(SomeModel.col1, SomeModel.col2)
根据您的要求，您可能还会发现递延有用。它们使您可以返回完整的对象，但可以限制导线上的列。
You can use the with_entities() method to restrict which columns you’d like to return in the result. (documentation)
result = SomeModel.query.with_entities(SomeModel.col1, SomeModel.col2)
Depending on your requirements, you may also find deferreds useful. They allow you to return the full object but restrict the columns that come over the wire.
回答 1
session.query().with_entities(SomeModel.col1)
是相同的
session.query(SomeModel.col1)
对于别名，我们可以使用.label（）
session.query(SomeModel.col1.label('some alias name'))
session.query().with_entities(SomeModel.col1)
is the same as
session.query(SomeModel.col1)
for alias, we can use .label()
session.query(SomeModel.col1.label('some alias name'))
回答 2
您可以使用load_only函数：
from sqlalchemy.orm import load_only
fields = ['name', 'addr', 'phone', 'url']
companies = session.query(SomeModel).options(load_only(*fields)).all()
You can use load_only function:
from sqlalchemy.orm import load_only
fields = ['name', 'addr', 'phone', 'url']
companies = session.query(SomeModel).options(load_only(*fields)).all()
回答 3
您可以使用Model.query，因为Model（通常是它的基类，尤其是在使用声明性扩展的情况下）已分配Sesssion.query_property。在这种情况下，Model.query相当于Session.query(Model)。
我不知道修改查询返回的列的方法（除非使用添加更多的方法add_columns()）。
因此，最好的选择是使用Session.query(Model.col1, Model.col2, ...)（如Salil所示）。
You can use Model.query, because the Model (or usually its base class, especially in cases where declarative extension is used) is assigned Sesssion.query_property. In this case the Model.query is equivalent to Session.query(Model).
I am not aware of the way to modify the columns returned by the query (except by adding more using add_columns()).
So your best shot is to use the Session.query(Model.col1, Model.col2, ...) (as already shown by Salil).
回答 4
您可以使用Query.values，Query.values
session.query(SomeModel).values('id', 'user')
You can use Query.values, Query.values
session.query(SomeModel).values('id', 'user')
回答 5
这里的一个例子：
movies = Movie.query.filter(Movie.rating != 0).order_by(desc(Movie.rating)).all()
我在数据库中查询评级为<> 0的电影，然后首先按最高评级对它们进行评级。
在这里看看：在Flask-SQLAlchemy中选择，插入，删除
An example here:
movies = Movie.query.filter(Movie.rating != 0).order_by(desc(Movie.rating)).all()
I query the db for movies with rating <> 0, and then I order them by rating with the higest rating first.
Take a look here: Select, Insert, Delete in Flask-SQLAlchemy
