As I understood in the blockchain, it is "not" possible to interact with webservices outside the blockchain. This must be done over oracles in order to verfiy that the request is secure, and the state change can be done in the blockchain. Please correct me, if I am wrong.

I am currently working with Testrpc, Truffle, and React in order to test my smart contract. Now I want to integrate oraclize.it into my environment. What is the best way to do this?

I tried to copy the testexamples into my Contract folder, but in the contract there is this reference:

import "github.com/oraclize/ethereum-api/oraclizeAPI.sol";

How can I integrate this reference to my folder structure?

I tried to copy the following files to my contract folder:


But I got a couple of errors.

What's the best way to implement Oraclize with Truffle and Testrpc/Ganache?

2 Answers 2


It is very possible to use the Oraclize service with testrpc alongside truffle.

Firstly, you need to follow the naming convention of contract filenames in truffle. As per their docs:

Truffle expects your contract files to define contracts that match their filenames exactly

Therefore you should download the Oraclize API from the Oraclize github repo, here's a specific link to the file oraclizeAPI_0.4.sol. Download this to the truffle contracts folder of your working directory, and rename the file to usingOraclize.sol. This is required so at compilation time, truffle knows which specific contract to compile from within the file. The other alternative is to directly paste all of the API into the required contract, but adding and renaming the API itself is likely the most elegant solution I'm aware of at the moment.

Now you will be able to import the API on your other contracts within that folder by including import "usingOraclize.sol" at the beginning of them, and then specifying its inheritance on the proper contract within, assuming the name of the example contract you need the API in is named myContract, the inheritance method should looks like

contract myContract is usingOraclize {
    // your code

The next step is making it so that your private testrpc chain is able to communicate with the Oraclize service, giving it the ability to send requests and receive the results back. For this, you will need the ethereum-bridge. Git clone that repository into a separate folder somewhere. What the bridge will do is, as its name suggest, setup a bridge for you between the Oraclize service and your blockchain while it runs.

Once ethereum-bridge is properly set-up, testrpc should be configured to use a static set of addresses, as the bridge will be dependent upon a specified address for deploying its required contracts on your private testrpc chain, therefore if you want those addresses to stay constant, between testrpc runs, you should be running testrpc with some re-usable addresses. You can do this by adding the --mnemonic flag when starting it, and using the same mnemonic phrase over when restarting testrpc, to ensure it generates the same Oraclize OAR (OraclizeAddressResolver), which you will need to use in the next step.

Now, we will need to find out the OAR that gets generated by the bridge.

  1. Start testrpc using a specific mnemonic phrase, and take note of the index of the last available account, (you can use any for this, but I recommend the last one, as it's an account that shouldn't be used in tests, also make sure enough other accounts were generated for you to be able to do tests using). Here's an example startup parameter:

testrpc --mnemonic "my test example" --accounts 50

Since 50 accounts are generated, the last address' index is 49.

  1. Run the eth-bridge, and get the OAR that is generated using this testrpc chain. I am assuming testrpc is running on the default RPC host:port of localhost:8545, if not you will need additional paramaters. Go to the root directory where ethereum-bridge is, and run the following command in a terminal.

node bridge -a 49

The following part of step 2 only needs to be done on your first-run

Now wait, until you see the line:

Please add this line to your contract constructor:

OAR = OraclizeAddrResolverI(0x145437eac36aeacee0c135c9015fff316ba938ed);

Your address should of course be different, as you'd be using a different mnemonic phrase. Add that specific line, right at the beginning of your myContract constructor so that it looks like this:

contract myContract is usingOraclize {
    function myContract() {
        OAR = OraclizeAddrResolverI(0x145437eac36aeacee0c135c9015fff316ba938ed);
        // rest of your constructor code
    // your code
  1. Now you are ready to begin compilation on truffle and making any tests you need for it, just ensure you always run steps 1 and 2 with the same parameters, and you won't have to change the OAR from within the contracts! (Do remember to remove the OAR variable from your constructor before production, this is just for testing, in production it will automatically fetch the OAR depending on the chain you're running it, currently the Mainnet, Ropsten, and browser-solidity VM environment are supported.)
  • 1
    Additionally, once this is all up and running; to successfully complete a query without an invalid jump exception (throw), the contract doing the oracle request, must have a sufficient positive balance of ether. This is a requirement even on testnets, as the ethereum-bridge emulates it as a production environment, so therefore expects there to be sufficient ether for the callback address, to actually cover the callback once the query comes in!
    – DenisM
    Commented Jan 15, 2017 at 21:14
  • Every time I launch node -a 49 I get a different address for the OAR to put in my constructor. Also how can I test queries that get run in the future Commented Apr 15, 2017 at 21:10
  • If you're using the newest ethereum-bridge version, it should actually always be the same constant OAR, even without a constant mnemonic phrase used for testrpc. Do note, if you're relaunching the ethereum-bridge for whatever reason, you should relaunch testrpc alongside it, or revert it to a clean snapshot.
    – DenisM
    Commented Apr 17, 2017 at 19:44
  • NOTE it's a good idea to run the bridge with the --dev flag if using testrpc, which circumvents the myid was triggered, but it was already seen before, skipping event... error, in the case of replayed logs, which may happen with a testrpc instance using snapshots etc...
    – DenisM
    Commented Nov 27, 2017 at 17:16
  • @DenisM do i need to keep the ethereum-bridge node application running after the OAR contract has been deployed on my network ?
    – amitKumar
    Commented Feb 10, 2021 at 11:24

These instructions appear to work (the bridge script runs ok) but when I actually make a call, I get a "key not found in the database" error.


Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.