Flask SQLAlchemy query, specify column names
Question:
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?
Answers:
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'))
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
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).
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.
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()
You can use Query.values, Query.values
session.query(SomeModel).values('id', 'user')
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']
I usually use this snippet:
fields = ["col1", "col2", ...]
session.query(map(lambda x: getattr(SomeModel.c, x), fields))
result = ModalName.query.add_columns(ModelName.colname, ModelName.colname)
An alternate syntax to fetch entity with specific columns:
any_query.with_entities(Entity).options(load_only(Entity.col))
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?
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'))
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
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).
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.
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()
You can use Query.values, Query.values
session.query(SomeModel).values('id', 'user')
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']
I usually use this snippet:
fields = ["col1", "col2", ...]
session.query(map(lambda x: getattr(SomeModel.c, x), fields))
result = ModalName.query.add_columns(ModelName.colname, ModelName.colname)
An alternate syntax to fetch entity with specific columns:
any_query.with_entities(Entity).options(load_only(Entity.col))