docs: add Contract.providerOrAccount explanation in migration guide

[PhilippeR26]

Motivation and Resolution

Add in the migration guide an explanation to connect an account to a contract after contract instantiation.
v7:

myContract.connect(myAccount);

v8:

myContract.providerOrAccount = myAccount;

Usage related changes

N/A

Development related changes

N/A

Checklist:

• Rebased to the last commit of the target branch (or merged it into my branch)

[penovicp]

The account isn't optional here.

[PhilippeR26]

Strange, because here it's optional :

const myTestContract = new Contract({ abi: compiledSierra.abi, address: deployResponse.contract_address });
  myTestContract.providerOrAccount = account0;

[PhilippeR26]

type ContractOptions = {
    abi: Abi;
    address: string;
    /**
     * Connect account to read and write methods
     * Connect provider to read methods
     * @default defaultProvider
     */
    providerOrAccount?: ProviderOrAccount;
    /**
     * Class hash of the contract
     */
    classHash?: string;
} & CommonContractOptions;

[PhilippeR26]

Shouldn't it be same concept in both?

[tabaktoni]

No because you cant do factory aka. Nor declare nor deploy without account.

To be honest optional provider or account on main class has no sense either, because without it you cant do anything with contract class

[tabaktoni]

I think this should be non-optional in both

[PhilippeR26]

Not sure.

• Create a Contract without account/provider : I have seen this case to use myContract.functions() to get a list of functions of a contract.
• Create a Contract with just a provider : Used to read Starknet (not write). Useful because you can read Starknet without asking to the user to connect an account.
• Create a Contract with an account: Used to write Starknet.

[tabaktoni]

• Create a Contract with just a provider : Used to read Starknet (not write). Useful because you can read Starknet without asking to the user to connect an account.
• Create a Contract with an account: Used to write Starknet.

Both these cases require a provider, so in those it is not optional.

• Create a Contract without account/provider : I have seen this case to use myContract.functions() to get a list of functions of a contract.

There are better ways to extract a function, but let say this is the simplest one; in that case, one can provide a default or a dummy provider. However, this is an extreme edge case; one should use the Calldata parser to do this.