SQLAlchemy declarative. Specify columns to select

Question

Declarative base:

Base = declarative_base()
Base.query = Session.query_property()

The class:

class Cheat(Base):

  __tablename__ = 'cheats'

  id = Column(Integer, primary_key = True, autoincrement = True)
  cheat = Column(Text)
  name = Column(String(255), index = True)
  _html = Column('html', Text)
  _slug = Column('slug', String(255))

  @hybrid_property
  def html(self):
    return self._html

  @html.setter
  def set_html(self, md):
    from markdown import markdown
    self._html = markdown(md)

  @hybrid_property
  def slug(self):
    return self._slug

  @slug.setter
  def set_slug(self, name):
    self._slug = slugify(name)

  def __init__(self, name, cheat):
    self.name = name
    self.slug = name
    self.cheat = cheat
    self.html = cheat

  def __repr__(self):
    return "Cheat<%s>" % self.name

Now I can get everything from the cheats:

Cheat.query.all()

and SQLAlchemy will generate SQL statement similar to:

SELECT name, slug, cheat, html FROM cheats

but I want my SQL statement to be:

SELECT name, slug FROM cheats

so I need to specify which columns I want to retrieve, because I don't really need to pull heavy texts from the database over the network. How do I do that?

Answer 1

define them as deferred, then they will only be fetched when the're accessed

from sqlalchemy.orm import deferred

class Cheat(Base):

  __tablename__ = 'cheats'

  id = Column(Integer, primary_key = True, autoincrement = True)
  cheat = deferred(Column(Text))
  name = Column(String(255), index = True)
  _html = Column('html', Text)
  _slug = deferred(Column('slug', String(255)))