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Uses to return a single cell value from any table or sql request on Tableland
// SPDX-License-Identifier: UNLICENSED
pragma solidity ^0.8.17;
import "@openzeppelin/contracts/utils/Strings.sol";
import "@openzeppelin/contracts/utils/structs/EnumerableMap.sol";
interface IMidpoint {
function callMidpoint(uint64 midpointId, bytes calldata _data) external returns(uint256 requestId);
interface IStringCallback {
function stringResponse(uint256 requestId, string memory data) external;
contract QueryController {
// will be used for recalling callbacks
using EnumerableMap for EnumerableMap.UintToAddressMap;
// emits when requests come in
event RequestMade(uint256 requestId, string network, string query);
// emits when midpoint responses come in
event ResponseReceived(uint256 requestId, string response);
// the midpoint contract
address constant midpoint = 0x9BEa2A4C2d84334287D60D6c36Ab45CB453821eB;
// the addr of the midpoint responses
address constant midpointOrigin = 0xC0FFEE4a3A2D488B138d090b8112875B90b5e6D9;
// the id of our query type
uint64 midpointID = 389;
// recalling callbacks
// mapping(uint256 => address) public callbacks;
EnumerableMap.UintToAddressMap private callbacks;
// just the basic call, no callback recorded
function _queryString(string memory column, string memory query) private returns(uint256 requestId) {
string memory wrapped = string.concat(
"SELECT ", column, " as response FROM (", query,") LIMIT 1"
bytes memory args = abi.encodePacked(wrapped, bytes1(0x00));
requestId = IMidpoint(midpoint).callMidpoint(midpointID, args);
emit RequestMade(requestId, wrapped, query);
return requestId;
// call midpoint w/ a callback to your own contract. contract must conform to IStringCallback
function queryString(string memory column, string memory query, address endpoint) public returns(uint256 requestId) {
// create a requestid from midpoint
requestId = _queryString(column, query);
EnumerableMap.set(callbacks, requestId, endpoint);
return requestId;
function callback(uint256 _requestId, uint64 _midpointId, string memory response) public {
// Only allow the verified callback address to submit information for your midpoint.
require(tx.origin == midpointOrigin, "Invalid callback address");
require(midpointID == _midpointId, "Invalid Midpoint ID");
if (EnumerableMap.contains(callbacks, _requestId)) {
address to = EnumerableMap.get(callbacks, _requestId);
EnumerableMap.remove(callbacks, _requestId);
IStringCallback(to).stringResponse(_requestId, response);
// For Demonstration Purposes Only
emit ResponseReceived(_requestId, response);
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