Thanks, it worked.
If someone is interested:
class UrlBundle(Bundle):
def __init__(self, *args, suffix='', **kwargs):
super().__init__(*args, **kwargs)
self._suffix = suffix
def create_row_processor(self, query, procs, labels):
s_proc = super().create_row_processor(query, procs,
labels)
suffix = self._suffix
def proc(row, a):
entity = s_proc(row, a)
return get_url(entity.id, entity.file_name,
entity.storage_type, suffix)
return proc
class File(Base):
id = Column(Integer, primary_key=True)
file_name = Column(Unicode(255))
storage_type = Column(EnumInt(STORAGE_TYPE))
@hybrid_method
def get_url(self, suffix=''):
return get_url(self.id, self.file_name, self.storage_type, suffix)
@get_url.expression
def get_url(cls, suffix=''):
return UrlBundle('url', cls.id, cls.file_name, cls.storage_type,
suffix=suffix)
And now I can do queries such as:
session.query(File.get_url('150x150')).filter_by(id=123)
On Tuesday, September 22, 2015 at 4:33:51 PM UTC+3, Michael Bayer wrote:
>
>
>
> On 9/22/15 7:18 AM, Yegor Roganov wrote:
>
> I know that I can encapsulate multiple columns into one using either
> composite column or hybrid_property, but unfortunatelly neither suits me
> 100%.
>
> Let's say I have a `File` model which includes fields `id`, 'file_name`,
> `storage_type`,
> and there is a `get_url` python function that when given `id`, 'file_name`
> and `storage_type` returns the constructed url.
>
> I want know to have a computed property `url` on the `File` model and be
> able to make queries such as
> ```
> f = session.query(File.url).filter_by(id=1).first()
> f[0] # should be a url returned by `get_url(f.id, f.file_name,
> f.storage_type)`
> ```
>
> I obviously cannot use `hybrid_property` since it only allows sql (which
> is expected).
> What comes very close is `sqlalchemy.orm.composite`.
> I can define composite class such as:
> ```
> class UrlComposite:
> def __init__(self, id, file_name, storage_type):
> self.id = id
> self.file_name = file_name
> self.storage_type = storage_type
>
> def __composite_values__(self):
> return self.id, self.file_name, self.storage_type
>
> def __eq__(self, other):
> return self.id == other.id and self.file_name == other.file_name\
> and self.storage_type == other.storage_type
>
> def __ne__(self, other):
> return not self.__eq__(other)
>
> def get(self'):
> return get_url(self.id, self.file_name, self.storage_type)
> ```
> Then I can do:
> ```
> f = session.query(File.url).filter_by(id=1).first()
> f[0].get() # extra get!
> ```
> it's almost what I wanted, but know to obtain the url I need to call a
> getter method on `UrlComposite`, which ideally I'd like to avoid. Is this
> possible?
>
> probably a Bundle can do this, since you can write your own
> create_row_processor method to return whatever you want, see
> http://docs.sqlalchemy.org/en/rel_1_0/orm/loading_columns.html?highlight=bundle#column-bundles
>
>
>
> I hope my question is clear, thanks in advance!
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