Flask SQLAlchemy query, specify column names
PythonSqlalchemyFlask SqlalchemyPython Problem Overview
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?
Python Solutions
Solution 1 - Python
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](http://docs.sqlalchemy.org/en/latest/orm/loading_columns.html#deferred "SQLAlchemy deferred column loading") useful. They allow you to return the full object but restrict the columns that come over the wire.
Solution 2 - Python
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'))
Solution 3 - Python
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()
Solution 4 - Python
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).
Solution 5 - Python
You can use Query.values, Query.values
session.query(SomeModel).values('id', 'user')
Solution 6 - Python
I usually use this snippet:
fields = ["col1", "col2", ...]\
session.query(map(lambda x: getattr(SomeModel.c, x), fields))
Solution 7 - Python
result = ModalName.query.add_columns(ModelName.colname, ModelName.colname)
Solution 8 - Python
As session.query(SomeModel.col1) returns an array of tuples like this [('value_1',),('value_2',)] if you want t cast the result to a plain array you can do it by using one of the following statements:
values = [value[0] for value in session.query(SomeModel.col1)]
values = [model.col1 for model in session.query(SomeModel).options(load_only('col1'))]
Result:
['value_1', 'value_2']
Solution 9 - Python
An alternate syntax to fetch entity with specific columns:
any_query.with_entities(Entity).options(load_only(Entity.col))
Solution 10 - Python
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