When should we call( ), watch( ) or get ( ) an event? which is the fastest way to get your data from the smart contract?

Question

Q1. I find this concept to be very confusing, when should I be using watch, call or get to listen to an event? how are they different and when should they be used?

Also,

var event1 = newInst.getSupplier({'OwnAdd': someaddr},{fromBlock:'latest, toBlock:'pending'}, function(error, result) {
    console.log("listening bro1");
    if (!error)
        console.log(result.args);
});

It returns me the structure twice.

{OwnAdd: "0xfd4e38348590a41e91b5ee57b69b99e746783990", _NameoProd: "lime", _QuantityoProd: BigNumber, _MnfofProd: "Done", _toSrv: "Meh", …}OwnAdd: "0xfd4e38348590a41e91b5ee57b69b99e746783990"_MnfofProd: "Done"_NameoProd: "lime"_QuantityoProd: BigNumber {s: 1, e: 1, c: Array(1)}_comments: "Bajaj"_status: "Saul "_toSrv: "Meh"__proto__: Object
eventwatcher.html:327 listening bro1
eventwatcher.html:329 {OwnAdd: "0xfd4e38348590a41e91b5ee57b69b99e746783990", _NameoProd: "lime", _QuantityoProd: BigNumber, _MnfofProd: "Done", _toSrv: "Meh", …}OwnAdd: "0xfd4e38348590a41e91b5ee57b69b99e746783990"_MnfofProd: "Done"_NameoProd: "lime"_QuantityoProd: BigNumber {s: 1, e: 1, c: Array(1)}_comments: "Bajaj"_status: "Saul "_toSrv: "Meh"__proto__: Object

Q2. I can't figure out why it sends me twice, can anyone figure this out? Note: I am just trying to get the pending data and not all the records with the above event

Smart Contract:

pragma solidity ^0.4.20;

contract Supplier{
    struct supply{
        string NameoProd;
        uint QuantityoProd;
        string MnfofProd;
        string toSrv;
        string stat;
        string comments;
    }
    uint SaleID=100000;
    mapping (uint=>supply) fmr;
    event getSupplier( address indexed OwnAdd, string _NameoProd,
        uint _QuantityoProd,
        string _MnfofProd,
        string _toSrv,
        string _status,
        string _comments);

    function setSupply(string _NameoProd,
        uint _QuantityoProd,
        string _MnfofProd,
        string _toSrv,
        string _status,
        string _comments) public{
        address snd = msg.sender;
        fmr[SaleID]=supply(_NameoProd,_QuantityoProd,_MnfofProd,_toSrv,_status,_comments);
        emit getSupplier(snd, _NameoProd,_QuantityoProd,_MnfofProd,_toSrv,_status,_comments);
        SaleID++;
    }
  function getSomething(uint ID) public view returns (string , uint  , string , string , string , 
    string  ){
        supply a=fmr[ID];
       return (a.NameoProd, a.QuantityoProd, a.MnfofProd, a.toSrv, a.stat, a.comments);
    }
    function update(uint ID, string rpf) public {
        supply b =fmr[ID];
        b.stat=rpf;
        fmr[ID]=b;
        emit getSupplier(msg.sender, b.NameoProd,b.QuantityoProd,b.MnfofProd,b.toSrv,b.stat,b.comments);
    }

    }

Q3. To get values back to a UI is it more feasible to get the data ID by ID or is it better to use events (what I am trying to achieve now). If I use events then when I call update I will get all the records from the events on page reload. I will have the old records as well as new record for that SupplyID. I can write a filter on the Dapp but can something else be done?

Answer 1

For events you only have event.watch() and event.get() (event() is equivalent to event.watch()).

• event.get() will return existing events between the two blocks passed as parameters. A dapp can use it to rebuild the current state of the contract.

• event.watch() will start listening for future events. A dapp can use it to keep the state up to date.

For the duplicated events it might be that you have two separate listeners watching events, or your contract is generating the two events.

Sometimes setting an event watch filtering with the user address can work. But it depends on the specifics of your design.