Query the first object of all user related objects in Django-CodePudding

I have a django model like below:

class Books:
    name = models.CharField(max_length=255)
    author = models.ForeignKey(User, on_delete=models.CASCADE)
    timeStamp = models.DateTimeField(auto_now_add=True)
    first = models.BooleanField(default=False)

I already have like a million entries in the Books table and added first field recently. Now I want to update the first field of the first created object of every user to True.

all = Books.objects.all()
li = []
for i in all:
   if i.user.username not in li:
       i.first = True
       i.save()
       li.append(i.user.username)

I tried the following function but it takes so long to execute, with much data in it. So is there a faster way? Tried the bulk_update method, for that also the loop should be completed.

CodePudding user response：

Because you are using PostgreSQL you can call .distinct() on specific column, and after that use queryset .update() method to update all columns to same value which should be a lof faster.

Books.objects.all().order_by('timeStamp').distinct('author').update(first=True)

Code above first orders queryset by timeStamp field, after that calling distinct on author column leaving only first distinct row (earliest) and in the end updates column value.