Contract view function

What is contract view function

A contract view function is a type of function in a blockchain smart contract that allows users to view or read the state of the contract without making any modifications. These functions are non-mutating, meaning they do not change any state on the blockchain and do not require any gas fees for execution. They are typically used to retrieve information from a contract, such as balances or stored data.

The view functions in contracts allow you to read the state of the smart contract, and we can create table functions to analyze them.

How to create

E.g. If we want to create table function for ERC20 balanceOf view function:

    /**
     * @notice Get the number of tokens held by the `account`
     * @param account The address of the account to get the balance of
     * @return The number of tokens held
     */
    function balanceOf(address account) external view returns (uint) {
        return balances[account];
    }

Its JSON ABI is:

{
 "constant":true,
 "inputs":[
   {"internalType":"address","name":"account","type":"address"}
  ],
 "name":"balanceOf",
 "outputs":[
   {"internalType":"uint256","name":"","type":"uint256"}
  ],
  "payable":false,
  "stateMutability":"view",
  "type":"function"
}

Create a table function for balanceOf:

pragma blockduck_create_contract_view_rpc(balanceOf, '{"constant":true,"inputs":[{"internalType":"address","name":"account","type":"address"}],"name":"balanceOf","outputs":[{"internalType":"uint256","name":"","type":"uint256"}],"payable":false,"stateMutability":"view","type":"function"}');

inputs

Args	Types	Info
suffix	VARCHAR	Table function suffix to identify the specific view
event_abi	VARCHAR	JSON ABI of the view function to be monitored

examples

D pragma blockduck_create_contract_view_rpc(balanceOf, '{"constant":true,"inputs":[{"internalType":"address","name":"account","type":"address"}],"name":"balanceOf","outputs":[{"internalType":"uint256","name":"","type":"uint256"}],"payable":false,"stateMutability":"view","type":"function"}');
┌─────────┐
│ Success │
│ boolean │
├─────────┤
│ 0 rows  │
└─────────┘

How to query

After that, table function named eth_contract_view_rpc_balanceOf already been created. Then you can try to query from it.

Inputs

Args	Types	Info
address	LIST(VARCHAR)	Contract address emitting the event
fromBlock	BigInt	Block number to start scanning from
toBlock	BigInt	Block number to stop scanning at
arg0	...	...
...	...	...
argn	...	inputs of the view function. Must be '0x' prefixed.
url	VARCHAR	URL of the Ethereum node

Examples

set variable eth_url = 'https://eth-mainnet.g.alchemy.com/v2/{API_KEY}';
select * from eth_contract_view_rpc_balanceOf(['0x1f9840a85d5aF5bf1D1762F925BDADdC4201F984']::varchar[], 21104077, 21104078, '0xD66428f5754db6126059314275676B2820e09135', getvariable('eth_url'));
┌────────────────────────────────────────────┬──────────┬──────────────────────┐
│                  address                   │  block   │      balanceOf0      │
│                  varchar                   │  int64   │        varint        │
├────────────────────────────────────────────┼──────────┼──────────────────────┤
│ 0x1f9840a85d5aF5bf1D1762F925BDADdC4201F984 │ 21104077 │ 0                    │
│ 0x1f9840a85d5aF5bf1D1762F925BDADdC4201F984 │ 21104078 │ 20166875074384524618 │
└────────────────────────────────────────────┴──────────┴──────────────────────┘

Dependent RPC Method

• eth_call