We are trying to develop a Dapp through which user can save some information in blockchain. We want to use this application as a storage of data so that later point of time user can query on that. do we need smart contract in this case?

For example, 1000 users(accounts) are simply saving their identity in the block chain.


2 Answers 2


You have a 'data' field in every transaction that can be used to store information (It works in similar way to the OP_RETURN opcode from Bitcoin, ie it is considered opaque by the protocol).

But retrieving and processing the information stored in that way will be more difficult that writing a simple contract.

For example you cannot delete a 'data' field from an existing transaction, so you have to define some way to declare such data as no longer valid. In a contract it is trivial to override or delete old data.

Ultimately as stated in the comments it depends on your particular use case.

  • Thank You Ismael for the explanation. Could you please help to understand the difference in data storage, in blockchain block for normal transaction and using smart contract transaction.
    – Sarmin
    Aug 11, 2017 at 6:14
  • Let's say that each contract has its own storage where they can read/write data. The content of the storage is not directly part of the blockchain, but its content is secured by the stateRoot field in a block that represent the result of applying each transaction in the block. It is expensive if you want to store massive amounts of data, there are other alternatives like Swarm or Ipfs.
    – Ismael
    Aug 11, 2017 at 18:18

You are trying to use a solid technology for the wrong purpose. As your title or the language suggests "smart contract", see the word there "contract". Now ask yourself, what agreement/contract are you possibly getting 1000+ users into by saving their data on the Ethereum blockchain? The smart contract works best with financial cases (but not exclusive) and in cases where a third party is needed. If you can sit down and tell me the sort of agreement you are getting into and the third party involved then, and only then, can you go into Ethereum (even if it doesn't make sense). Dearest Sarmin, your case doesn't need a DApp. Thank you.

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.