model.py

""" Copyright 2022 Google LLC

 Licensed under the Apache License, Version 2.0 (the "License");
 you may not use this file except in compliance with the License.
 You may obtain a copy of the License at

      http://www.apache.org/licenses/LICENSE-2.0

 Unless required by applicable law or agreed to in writing, software
 distributed under the License is distributed on an "AS IS" BASIS,
 WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 See the License for the specific language governing permissions and
 limitations under the License.
"""

from sqlalchemy import Column, Integer, String, Boolean, LargeBinary, Float, \
  Numeric, DateTime, Date, FetchedValue, ForeignKey, ColumnDefault
from sqlalchemy.orm import registry, relationship
from sqlalchemy.dialects.postgresql import JSONB, ARRAY
from datetime import timezone, datetime

mapper_registry = registry()
Base = mapper_registry.generate_base()


def format_timestamp(timestamp: datetime) -> str:
  return timestamp.astimezone(timezone.utc).isoformat() if timestamp else None


"""
 BaseMixin contains properties that are common to all models in this sample.
 
 The created_at and updated_at properties are automatically filled with the
 current client system time when a model is created or updated.
"""
class BaseMixin(object):
  __prepare_statements__ = None

  version_id = Column(Integer, nullable=False)
  created_at = Column(DateTime(timezone=True),
                      # We need to explicitly format the timestamps with a
                      # timezone to ensure that SQLAlchemy uses a
                      # timestamptz instead of just timestamp.
                      ColumnDefault(datetime.utcnow().astimezone(timezone.utc)))
  updated_at = Column(DateTime(timezone=True),
                      ColumnDefault(
                        datetime.utcnow().astimezone(timezone.utc),
                        for_update=True))
  __mapper_args__ = {"version_id_col": version_id}


"""
 BaseUuidMixin is the base class for all tables that use a client-side
 generated UUID as the primary key.
""" 
class BaseUuidMixin(BaseMixin):
  id = Column(String, primary_key=True)


"""
 BaseInt64Mixin is the base class for all tables that use an auto-generated
 INT64 as the primary key. The value is generated by a bit-reversed sequence
 in the database.
"""
class BaseInt64Mixin(BaseMixin):
  id = Column(Integer, primary_key=True)


class Singer(BaseUuidMixin, Base):
  __tablename__ = "singers"

  first_name = Column(String(100))
  last_name = Column(String(200))
  full_name = Column(String,
                     server_default=FetchedValue(),
                     server_onupdate=FetchedValue())
  active = Column(Boolean)
  albums = relationship("Album", back_populates="singer")

  __mapper_args__ = {
    "eager_defaults": True,
    "version_id_col": BaseMixin.version_id
  }

  def __repr__(self):
    return (
      f"singers("
      f"id={self.id!r},"
      f"first_name={self.first_name!r},"
      f"last_name={self.last_name!r},"
      f"active={self.active!r},"
      f"created_at={format_timestamp(self.created_at)!r},"
      f"updated_at={format_timestamp(self.updated_at)!r}"
      f")"
    )


class Album(BaseUuidMixin, Base):
  __tablename__ = "albums"

  title = Column(String(200))
  marketing_budget = Column(Numeric)
  release_date = Column(Date)
  cover_picture = Column(LargeBinary)
  singer_id = Column(String, ForeignKey("singers.id"))
  singer = relationship("Singer", back_populates="albums")
  # The `tracks` relationship uses passive_deletes=True, because `tracks` is
  # interleaved in `albums` with `ON DELETE CASCADE`. This prevents SQLAlchemy
  # from deleting the related tracks when an album is deleted, and lets the
  # database handle it.
  tracks = relationship("Track", back_populates="album", passive_deletes=True)

  def __repr__(self):
    return (
      f"albums("
      f"id={self.id!r},"
      f"title={self.title!r},"
      f"marketing_budget={self.marketing_budget!r},"
      f"release_date={self.release_date!r},"
      f"cover_picture={self.cover_picture!r},"
      f"singer={self.singer_id!r},"
      f"created_at={format_timestamp(self.created_at)!r},"
      f"updated_at={format_timestamp(self.updated_at)!r}"
      f")"
    )


class Track(BaseUuidMixin, Base):
  __tablename__ = "tracks"

  id = Column(String, ForeignKey("albums.id"), primary_key=True)
  track_number = Column(Integer, primary_key=True)
  title = Column(String)
  sample_rate = Column(Float)
  album = relationship("Album", back_populates="tracks")

  def __repr__(self):
    return (
      f"tracks("
      f"id={self.id!r},"
      f"track_number={self.track_number!r},"
      f"title={self.title!r},"
      f"sample_rate={self.sample_rate!r},"
      f"created_at={format_timestamp(self.created_at)!r},"
      f"updated_at={format_timestamp(self.updated_at)!r}"
      f")"
    )


class Venue(BaseUuidMixin, Base):
  __tablename__ = "venues"

  name = Column(String(200))
  description = Column(JSONB)

  def __repr__(self):
    return (
      f"venues("
      f"id={self.id!r},"
      f"name={self.name!r},"
      f"description={self.description!r},"
      f"created_at={format_timestamp(self.created_at)!r},"
      f"updated_at={format_timestamp(self.updated_at)!r}"
      f")"
    )


class Concert(BaseUuidMixin, Base):
  __tablename__ = "concerts"

  name = Column(String(200))
  venue_id = Column(String, ForeignKey("venues.id"))
  venue = relationship("Venue")
  singer_id = Column(String, ForeignKey("singers.id"))
  singer = relationship("Singer")
  start_time = Column(DateTime(timezone=True))
  end_time = Column(DateTime(timezone=True))
  ticket_sales = relationship("TicketSale", back_populates="concert")

  def __repr__(self):
    return (
      f"concerts("
      f"id={self.id!r},"
      f"name={self.name!r},"
      f"venue={self.venue!r},"
      f"singer={self.singer!r},"
      f"start_time={self.start_time!r},"
      f"end_time={self.end_time!r},"
      f"created_at={format_timestamp(self.created_at)!r},"
      f"updated_at={format_timestamp(self.updated_at)!r}"
      f")"
    )


class TicketSale(BaseInt64Mixin, Base):
  __tablename__ = "ticket_sales"

  concert_id = Column(String, ForeignKey("concerts.id"))
  concert = relationship("Concert")
  customer_name = Column(String)
  price = Column(Numeric)
  # "seats" has type text[] in the database. By not specifying any type here,
  # we ensure that SQLAlchemy just sends an untyped string value to the
  # database. If we were to configure the type to be ARRAY(String) here, then
  # we would get an error 'Array casting / coercion is not supported', as
  # SQLAlchemy would try to cast the value to a VARCHAR[].
  # TODO: Use this mapping when array casting/coercion is supported.
  #       seats = Column(ARRAY(String))
  seats = Column()

  def __repr__(self):
    return (
      f"ticket_sales("
      f"id={self.id!r},"
      f"concert={self.concert!r},"
      f"customer_name={self.customer_name!r},"
      f"price={self.price!r},"
      f"seats={self.seats!r},"
      f"created_at={format_timestamp(self.created_at)!r},"
      f"updated_at={format_timestamp(self.updated_at)!r}"
      f")"
    )