Bulk update of a model field based on a condition

I have a 5 column model with around 10,000+ lines of data. Now I want to update one column of all the lines based on other column values.

>Solution :

myModel = MyModel.objects.all()

for l in myModel:
    if c1=='ChkVal1' and c2 < c3:    
        c4='Value 1'
    elif c1=='ChkVal2' and c2 b> c3:
        c4='Value 2'
    else
        c4='Value 3'

MyModel.objects.bulk_update(myModel, update_fields = ['c4'])