Solidity JSON – How to Store JSON String in Solidity

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I have trying to store a JSON string in my solidity code string variable, it only stores the string on the constructor, but if try and store the same data in the function call it never saves it.

contract BOLData {

    string public SData;
    string public SCData;


    function BOLData(string S_Data) 
    { 
        SData= S_Data;
        SCData= '';
    } 
    function getSData() constant returns (string retVal) 
    { 
        return SData;
    }
    function setSCData(string SC_Data) 
    { 
        SCData = SC_Data; 
    } 
    function getSCData() constant returns (string retVal) 
    { 
        return SCData;
    }

}

Best Answer

Just gave it a try on Remix and seems to be working fine. using setSCData() does modify the value of SCData.

Maybe you are getting confused by the name of your variables... In the constructor you are setting SData but then the set function only deals with SCData, there's no function to update SData value.

Related Solutions

Solidity JSON Parsing – How to Parse JSON in Solidity

I'll assume that you want to call an external source on which you can't have control and that you use the json() Oraclize datasource in order to get only the right part of the service json that is returned when you call it's URL as indicated in Oraclize Available Datasources documentation.

For now I think you have no way to make Oraclize return anything else than a string. That means that you have to get the returned Json as a string parameter of your oraclize __callback function.

But then, as you ask, you need to parse the json to an array. This would be very costly even if you find a way to do it.

So the short answer would be that what you ask is not possible.

However, let me suggest the following, not totally satisfactory, workarounds. I know it's just workarounds that probably won't fit your needs but I think that what you want to do is not possible for now, so let's just try to go closest as possible from the goal.

Workarounds:

use a proxy website that would be able to request you original service, the one you don't control, and parse the resulting json using whatever your can use as server side language. make it format the result as a single line string with separator (ie. a comma). Then tell Oraclize to query this proxy instead of the original service. Your contract will then get the string that will be more easy and cost efficient to parse and split. You can create a split function based on this Solidity string utils lib. Note that you won't find a split function to split your string in more than 2 slices in this lib but this is a good starting point.
With the Oraclize Json() URL function, you can use XPath to target a value in the JSON result. You could compare the cost of splitting a result string to the cost of calling Oraclize multiple times to target each result item separately. I can't say which is cheaper even if I guess that it really depends of the length of your result items strings.
If you use your contract from a Dapp only, I suggest you to call the original service directly with the client side JS and forget Oraclize, extract values from it and then call a method in which you could pass each value as a parameter. But I guess that if you use Oraclize it's probably that you want your contract to be autonomous.

[Ethereum] sending string parameter value to solidity method

Your method changes the state of the contract (block chain) meaning that you can't get any values since by the time the call returns the transaction (calling the method) may not have been mined (there is no computed id to return).

You will get the hash of the transaction and must wait until the code is executed (mined). Only then can you get the id by calling a method that does only a read operation over the contract.

You also need to assign a cost in gas to the transaction for the call since you are asking a miner to run it for you. Use the geth IPC since it's far less cumbersome than throwing JSON objects at the client:

entityContract.insert("my_string", {from:eth.accounts[0],gas:100000000});

where entityContract is a contract instance created from its ABI and address.

Best Answer

Related Solutions

Solidity JSON Parsing – How to Parse JSON in Solidity

[Ethereum] sending string parameter value to solidity method

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