HIP-873: Decimals are not returned with the token balance in the new token relationship API

[mehcode]

Description

A token balance without the associated number of decimals to know how to interpret that balance is dangerous to present to an end user.

Steps to reproduce

1. Query for token balances using the new /api/v1/accounts/{id}/tokens API.
2. See that decimal information is not returned.

Additional context

No response

Hedera network

mainnet, testnet, previewnet

Version

v1

Operating system

None

[xin-hedera]

Token decimal is immutable and can be retrieved from /api/v1/tokens/{id}.

We can't change how the value is presented in the existing property since that'll be a breaking change and cause issues for applications treating it properly.

[mehcode]

If I, as an end-user, fetch my balance for 50 tokens. I now need to call the mirror node 51 total times to be able to correctly use that information (balance + decimals).

It's not a breaking change to add a new decimals field to the response from /api/v1/accounts/{id}/tokens.

[steven-sheehy]

It would not be performant to join on token for /api/v1/accounts/{id}/tokens to add decimal since they have different distribution columns for our sharded database.

Instead, we could fix the bug that makes /api/v1/tokens?token.id=0.0.X&token.id=0.0.Y not work by ensuring it uses an IN clause. However, the list API doesn't show decimals currently so would require a HIP to add the field. But if that was in place your use case would only require 2 queries. Also note that decimals is immutable so even though it might require 50 lookups now you could cache it indefinitely within the app.