Move beginner doubt

[Shoydon]

Discord user ID

shoydon

Describe your question in detail.

Hello.... I am new to Move. I just wanted some help in my project

struct Card has key, store {
  id: u64,
  owner: address,
  ipfs_hash: String,
}

//global variables
let totalCardsCount = 0;
let CardsById: SimpleMap<u64, Card> = simple_map::create();
let myCards: SimpleMap<address, vector<u64>> = simple_map::create();  // stores the ids of cards i own

Can someone help me correct this code?
i am making a card collection app. I have made it using solidity, so i was trying to build it on aptos
Solidity code for reference:

struct Card {
  uint id;
  address owner;
  string ipfsHash;
}

uint public totalCardsCount;
mapping(uint => Card) public CardsById;
mapping(address => uint[]) public myCards;  

constructor() {
  totalCardsCount = 0;
}

What error, if any, are you getting?

No response

What have you tried or looked at? Or how can we reproduce the error?

No response

Which operating system are you using?

Windows

Which SDK or tool are you using? (if any)

N/A

Describe your environment or tooling in detail

No response

[ajaythxkur]

@Shoydon

module 0xCAFE::card {
    use std::signer;
    use aptos_std::simple_map::{Self, SimpleMap};
    use std::vector;
    use std::string::String;

    struct State has key {
        total_cards_count: u64,
        cards_by_id: SimpleMap<u64, Card>
    }

    struct MyCard has key {
        cards: SimpleMap<address, vector<u64>>,
    }

    struct Card has store, drop {
        id: u64,
        owner: address,
        ipfs_hash: String,
    }

    fun init_module(creator: &signer){
        move_to(creator, State {
            total_cards_count: 0,
            cards_by_id: simple_map::new(),
        })
    }

    entry fun add_card(user: &signer, ipfs_hash: String) acquires State, MyCard {
        let user_addr = signer::address_of(user);
        let state = borrow_global_mut<State>(@0xCAFE);
        let counter = state.total_cards_count + 1;
        let new_card = Card {
            id: counter,
            owner: user_addr,
            ipfs_hash,
        };
        if(!exists<MyCard>(user_addr)){
            let my_card = MyCard {
                cards: simple_map::new()
            };
            move_to(user, my_card);
        };
        let my_card = borrow_global_mut<MyCard>(user_addr);
        let user_card_idx = simple_map::borrow_mut(&mut my_card.cards, &user_addr);
        vector::push_back(user_card_idx, counter);
        simple_map::upsert(&mut state.cards_by_id, counter, new_card);
        state.total_cards_count = counter;
    }
}

[Shoydon]

Thanks! I'll check it out
@ajaythxkur do i need to write my address in place of the 0xCAFE ?

[Shoydon]

Hey @ajaythxkur I wrote the code for the view functions. Is this right?

#[view]
    public fun view_cards_count():u64 acquires State {
        let state = borrow_global_mut<State>(@my_addrx);
        state.total_cards_count
    }

#[view]
   public fun view_cards(): vector<Card> acquires State, Card {
        let state = borrow_global_mut<State>(@my_addrx);
        let cards = vector::empty<Card>();
        let count = state.total_cards_count;
        for (i in 1..(count+1)) {
            let temp = simple_map::borrow(&mut state.cards_by_id, &i);
            vector::push_back(&mut cards, temp);
        };
        cards
    }

[ajaythxkur]

@Shoydon you should not mut borrow anything in view function as you are not changing state

[Shoydon]

@ajaythxkur I see. Thanks for letting me know!