如何使此代码用于获取列表中的对象更短？

Question

I am retrieving database objects to add to a dict, but the keys can't be duplicates, so I've done it this way:

    carb1 = random.choice(carbs)
    protein1 = random.choice(proteins)
    carb2 = Food.objects.filter(category='Carbs').exclude(name=carb1.name)[0]
    protein2 = Food.objects.filter(category='Protein').exclude(name=protein1.name)[0]
    veg1 = random.choice(vegs)
    veg2 = Food.objects.filter(category='Vegetables').exclude(name=veg1.name)[0]

    meals = [carb1, protein1, carb2, protein2]

    exclude_these = [o.name for o in meals]

    carb3 = Food.objects.filter(category='Carbs').exclude(name__in=exclude_these)[0]
    protein3 = Food.objects.filter(category='Protein').exclude(name__in=exclude_these)[0]
    veg3 = Food.objects.filter(category='Vegetables').exclude(name__in=exclude_these)[0]
    meals.append(carb3)
    meals.append(protein3)
    meals.append(veg3)

    exclude_these = [o.name for o in meals]

    carb4 = Food.objects.filter(category='Carbs').exclude(name__in=exclude_these)[0]
    protein4 = Food.objects.filter(category='Protein').exclude(name__in=exclude_these)[0]
    veg4 = Food.objects.filter(category='Vegetables').exclude(name__in=exclude_these)[0]

    meals.append(carb4)
    meals.append(protein4)
    meals.append(veg4)

    exclude_these = [o.name for o in meals]

    carb5 = Food.objects.filter(category='Carbs').exclude(name__in=exclude_these)[0]
    protein5 = Food.objects.filter(category='Protein').exclude(name__in=exclude_these)[0]
    veg5 = Food.objects.filter(category='Vegetables').exclude(name__in=exclude_these)[0]

    meals.append(carb5)
    meals.append(protein5)
    meals.append(veg5)

    exclude_these = [o.name for o in meals]

    carb6 = Food.objects.filter(category='Carbs').exclude(name__in=exclude_these)[0]
    protein6 = Food.objects.filter(category='Protein').exclude(name__in=exclude_these)[0]
    veg6 = Food.objects.filter(category='Vegetables').exclude(name__in=exclude_these)[0]

But this just seems like a ridiculous amount of code to achieve what I want.

Is there a way I can shorten this?

Answer 1

It looks like you want to retrieve 6 carbs, 6 proteins, and 6 vegs from your foods table and you don't care which they are (you provide no ordering in the query and take the first of each). Except the first one is random. Maybe you don't care that the first one is picked at random or maybe you want the remaining 5 to be uniformly picked at random as well?

Here are some options:

carb1, carb2, carb3, carb4, carb5, carb6 = tuple(
    Food.objects.filter(category='Carbs')[:6]
)

And similar for portein and veg. Frankly, don't name your variables carbN, just put all of them in a list or tuple. carbs = Food....[:6]

If the name column is not unique and you really want 6 carbs that have different names,

carbs = Food.objects.filter(category='Carbs').distinct('name')[:6]

Distinct on a column instead of the whole record doesn't work in all database backends. It works in postgres, but I think it doesn't work in mysql.

If you really want 6 random carbs, you can have the database randomize it for you.

carbs = Food.objects.filter(category='Carbs').order_by('?')[:6]

There may be some performance problems with random ordering if your table of foods is large.