I have some questions that need clarification.

Lets say if I create a trade-in website using blockchain technology,

First, do I store all sort of data into blockchain such as user credentials, user info, product info, etc? I'm sure trade data between the users need to be stored in the blockchain, but what about other data I mentioned above?

Second, since user credentials are private data, shouldn't they be stored in other database like sql-server?

Third, if they can be stored and retrieved from other database, does ethereum dapp provide any functionality to pull those APIs? (ex: .Net Core API)

Last but not least, is it also a good approach to store other data such as each product information into blockchain? (worried about too much data in blockchain?)

Thanks in advance.

2 Answers 2


Looks like you are trying to replace a database with Blockchain, which would not be a great idea. I suggest you to think about why you bring in Blockchain to your solution. Ideally it should be something like you need such transaction to be trusted without depending on a third party. So the solution you are implementing has such information, it make sense to bring only such data into Blockchain.

Answers to your questions in brief.

  1. Store only the appropriate data in Blockchain. Store data in Blockchain cost you Ether (or relevant currency), so better to avoid any unnecessary data.

  2. By design, no credentials will be managed by Blockchain but depend on private/public keys for authentication. Try to leverage on Blockchain architecture which supports avoiding of saving even encrypted passwords.

  3. You do not need any support from web3.js to connect with external databases or APIs. Just do that part as in a regular app.

  1. using the Blockchain to store your data instead of a classic database, is very expensive. An article from July 2018, calculated that it would cost 17,500 ETH/GB

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