django-ormex 0.2

GroupConcat

Works like Concat, but for concatenating field values of related ManyToMany model. For instance, you may use it if you have an Author model as ManyToMany relation in the Book model (Book.authors = ManyToManyField(Author)) and you want to have concatenated list of all authors coupled to a given book.

Given the following models:

class Publisher(models.Model):
    """Publisher."""

    name = models.CharField(max_length=30)
    address = models.CharField(max_length=50)
    city = models.CharField(max_length=60)
    state_province = models.CharField(max_length=30)
    country = models.CharField(max_length=50)
    website = models.URLField()


class Author(models.Model):
    """Author."""

    salutation = models.CharField(max_length=10)
    name = models.CharField(max_length=200)
    email = models.EmailField()
    headshot = models.ImageField(upload_to='authors', null=True, blank=True)


class Book(models.Model):
    """Book."""

    title = models.CharField(max_length=100)
    authors = models.ManyToManyField('books.Author', related_name='books')
    publisher = models.ForeignKey(Publisher, related_name='books')
    publication_date = models.DateField()
    isbn = models.CharField(max_length=100, unique=True)
    price = models.DecimalField(max_digits=10, decimal_places=2)
    pages = models.PositiveIntegerField(default=200)
    stock_count = models.PositiveIntegerField(default=30)

We could use GroupConcat as follows:

from ormex.aggregations import GroupConcat

book = Book.objects.all() \
        .values('id',
                'title',
                'pages',
                'price',
                'publisher__id',
                'publisher__name') \
        .annotate(
            authors__name=GroupConcat('authors__name', separator=', ')
        ) \
        .first()

Output would look as follows:

{
    'authors__name': 'Finn Janssen, Dan Dijkman, Merel Wolf, Evy de Jong',
    'id': 14,
    'pages': 83,
    'price': Decimal('62.13'),
    'publisher__id': 19,
    'publisher__name': 'Rijn, de Bruyn and Verharen',
    'title': 'Laboriosam officia temporibus facere omnis odit.'
}