How to create a query and add columns to select sequentially?

问题

I need to construct a query where the selected columns in the result are changing. How can I add columns to the result progressively similar to .filter:

query = session.query(User).filter(name == 'Hansen').filter(country == 'Spain')

Thanks!

回答1:

The sqlalchemy Query class has an add_columns method that can be used for this.

cols = ['col1', 'col2', 'col3', 'col4']

q = session.query()
for c in cols:
    q = q.add_columns(getattr(MyTable, c)) 

res = q.all()

As the name suggests, the method will accept more than one column expression.

q.add_columns(*list_of_columns)

Query.add_entity would be used to add an orm entity, such as a model class, to the query.

q = session.query()
q = q.add_entity(MyTable)
# Fetch objects, not just columns
list_of_objs = q.all()

来源：https://stackoverflow.com/questions/57873787/how-to-create-a-query-and-add-columns-to-select-sequentially