from django.contrib.gis.db import models

class SimpleModel(models.Model):

    class Meta:

        abstract = True

class Location(SimpleModel):

    point = models.PointField()

    def __str__(self):

        return self.point.wkt

class City(SimpleModel):

    name = models.CharField(max_length=50)

    state = models.CharField(max_length=2)

    location = models.ForeignKey(Location, models.CASCADE)

    def __str__(self):

        return self.name

class AugmentedLocation(Location):

    extra_text = models.TextField(blank=True)

class DirectoryEntry(SimpleModel):

    listing_text = models.CharField(max_length=50)

    location = models.ForeignKey(AugmentedLocation, models.CASCADE)

class Parcel(SimpleModel):

    name = models.CharField(max_length=30)

    city = models.ForeignKey(City, models.CASCADE)

    center1 = models.PointField()

    # Throwing a curveball w/`db_column` here.

    center2 = models.PointField(srid=2276, db_column="mycenter")

    border1 = models.PolygonField()

    border2 = models.PolygonField(srid=2276)

    def __str__(self):

        return self.name

class Author(SimpleModel):

    name = models.CharField(max_length=100)

    dob = models.DateField()

class Article(SimpleModel):

    title = models.CharField(max_length=100)

    author = models.ForeignKey(Author, models.CASCADE, unique=True)

class Book(SimpleModel):

    title = models.CharField(max_length=100)

    author = models.ForeignKey(Author, models.SET_NULL, related_name="books", null=True)

class Event(SimpleModel):

    name = models.CharField(max_length=100)

    when = models.DateTimeField()