Speed up Django bulk_create with unique fields [duplicate]

Question

I have a database with thousands of entries. Each entry has a unique field that I called unique_id and it's calculated on some other fields:

class ModelA(models.Model):
    name = models.CharField(max_length=256, help_text="Type a name")
    created_at = models.DateTimeField(auto_now_add=True)
    unique_id = models.CharField(max_length=256, unique=True, editable=False, default=calculate_my_unique_id)

This is the algorithm I'm using to prevent duplicates (omitting a bit of code):

objectsToAdd = []

items_dict = ModelA.objects.in_bulk(field_name='unique_id')

unique_id = generate_unique_id()

if unique_id not in items_dict.keys():
    objectsToAdd.append( 
        ModelA(
            name=item_name, unique_id=unique_id
        )
    )

if objectsToAdd:
    ModelA.objects.bulk_create(objs=objectsToAdd)

The problem is that when table items grow, will grow also item_dict list and consequently the check time.

Is there a more efficient way to simply skip duplicates from bulk insert?

EDIT: If I use ignore_conflicts=True the bulk_create returns all objects I've tried to insert instead of those really created