CEI smart contract design framework for pickWinner function in lesson 9

[Kuusho]

In lesson 9 of the foundry course, Patrick mentioned the CEI smart contract design framework.

I'd like to ask, in the pickWinner function for the Raffle,

uint256 requestId = i_vrfCoordinator.requestRandomWords( i_gasLane, i_subscriptionId, REQUEST_CONFRIMATIONS, i_callbackGasLimit, NUM_WORDS }

does this part that involves interacting with Chainlink count as effects (since we imported the contracts) or are they interactions (because they are fetching data from chainlink)?

[xyz899]

Hi !

The following line you wrote is an Interaction ( meaning we fetch data ) because you are asking of the Chainlink VRF to get random words that let's you generate a uniqueId. So no, in order to get a generated Id we need to fetch the data from an external source, like you do when fetching the price of a supported token with AggregatorV3Interface for example.

winter99

[Kuusho]

Thanks for this answer! Absolutely well thought out, I appreciate it

[r0bchain]

Guys, I am trying to understand where the call to the Chainlink VRF is made. I see that the method is in an interface and does not implement the body of the method. Where is it implemented?
As I read, the implementation of the body is in VRFConsumerBaseV2.sol, but there is not this method, I only can see fulfillRandomWords but nothing about requestRandomWords , any clue?

  function requestRandomWords(
    bytes32 keyHash,
    uint64 subId,
    uint16 minimumRequestConfirmations,
    uint32 callbackGasLimit,
    uint32 numWords
  ) external returns (uint256 requestId);

[r0bchain]

Ok, I found the answer to my question here, I guess this is where the body of the method is located : https://github.com/smartcontractkit/chainlink/blob/develop/contracts/src/v0.8/vrf/dev/VRFCoordinatorV2_5.sol
I got it from the Chainlink VRF official documentation:
https://docs.chain.link/vrf/v2-5/overview/subscription

[EngrPips]

Yeah, You call the VRFCoordinatorV2_5 to request random words, and the VRFCoordinatorV2_5 will call your contract back, which must be a type of VRFConsumerBaseV2 to fulfill your request for random words.