django-ormex 0.1

GroupConcat

Works like Concat, but for concatenating field values of related ManyToMany model.

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

books = Book.objects.all() \
        .select_related('publisher') \
        .prefetch_related('authors') \
        .only('id',
              'title',
              'pages',
              'price',
              'publisher__id',
              'publisher__name',
              'authors__id',
              'authors__name') \
        .values('id',
                'title',
                'pages',
                'price',
                'publisher__id',
                'publisher__name') \
        .annotate(authors__name=GroupConcat('authors__name')) \
        .distinct()