models.py

from django.db import models

# Create your models here.
from cms.models import CMSPlugin, Model

class Forthcoming(Model):
    title = models.CharField(
        max_length=200,
        unique=True
    )
    series_list = (
        ('Sources', 'Sources'),
        ('Studies', 'Studies'),
        ('Proceedings', 'Proceedings'),
        ('Textbooks', 'Textbooks'),
    )
    series = models.CharField(max_length=20, choices=series_list)

    author = models.CharField(
        max_length=200,
        unique=True
    )
    description = models.CharField(
        max_length=1000
    )
    cover = models.ImageField(
        upload_to='eoaforthcoming/images'
    )

    # functions:
    def __str__(self):
        return self.title

class EOAForthcomingListModel(CMSPlugin):

    # functions:
    def __str__(self):
        return str(self.id)

class EOAForthcomingModel(CMSPlugin):
    eoaforthcoming = models.ForeignKey(
        Forthcoming, on_delete=models.CASCADE
    )

    # functions:
    def __str__(self):
        return self.eoaforthcoming.title

    @property
    def layout(self):
        instance, plugin_class = self.parent.get_plugin_instance()
        return instance.layout

    def copy_relations(self, oldinstance):
        # Because we have a ForeignKey, it's required to copy over
        # the reference to the referenced instance to the new plugin.
        self.eoaforthcoming = oldinstance.eoaforthcoming