[Django]-Can Django select_for_update be used to acquire a read lock?

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  1. Yes, your approach is pretty much right and it will acquire the lock for the first query and the rest will have to wait until the transaction is complete.

  2. If you are not using the version field for anything other than acquiring the lock, you can forcefully acquire a lock by forcefully evaluating the QuerySet using a list(). See the code below.

    @atomic_transaction
def func(product_id, amount_to_purchase):
    # Forcefully acquiring a lock
    product = list(Product.objects.select_for_update.filter(...))[0]

    if product.amount_available_for_purchase > amount_to_purchase:
      # do payment related stuff
      Purchase.objects.create(product=product, amount=amount_to_purchase)
      # do more stuff

Here you are acquiring the lock forcefully by evaluating the QuerySet like mentioned here in the docs.

👤PSN

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