add distinct_on option for queries

[maaft]

My project emits Event like this:

emit StateChanged(gameId, state);

I want to be able to query the most-recent event for a gameId. For example Hasura solves this with distinct_on query parameters.

I think that would be a great addition.

My current workaround is, to query all sorted and then do the filtering client side. This adds a lot of traffic overhead of course.

Or maybe there is another solution that I'm not aware of?

[joshstevens19]

why cant you use the order by and first 1 in the graphql aka like below?

query AllTransfers {
  allTransfers(first: 1, orderBy: [BLOCK_NUMBER_DESC]) {
    nodes {
      blockHash
      blockNumber
      contractAddress
      from
      network
      nodeId
      to
      txHash
      value
    }
    pageInfo {
      endCursor
      hasNextPage
      hasPreviousPage
      startCursor
    }
  }
}

https://rindexer.xyz/docs/accessing-data/graphql#ordering

[maaft]

I want to get a list of "most recent" games, not a single game.

In my case a GameEvent is defined by gameId and state. I want for example to get the first 10 games, unique by game_id, but ordered by block_number_desc. I don't see any possibility with current API to achieve such thing.

What I would like to do (see distinct_on param):

query GetGames {
  allGameEvents(first: 10 offset: 0 orderBy: [BLOCK_NUMBER_DESC], distinct_on: [game_id]) {
    nodes {
      gamedId
      blockNumber
      state
    }
    totalCount
  }
}

Without this, we have currently these limitations:

1. need to filter-out duplicate game_ids on client-side
2. not possible to reliably "fetch X unique games" since there can be multiple GameEvents for the same gameId in neighboring block-numbers. Example event ordering:

(gameId, state, block_number)
- 0, created, 0
- 0, active, 1
- 1, created, 2
- 2, created, 3

When I want to fetch let's say most recent 3 unique games for my pagination so I set first: 3, with current API I'll get on client-side:

- 0, created, 0
- 0, active, 1
- 1, created, 2

After filtering this list will be:

- 0, active, 1
- 1, created, 2

So my pagination breaks.

[maaft]

maybe custom queries could be an option?

https://www.graphile.org/postgraphile/custom-queries/

Update:

yep, solved it with custom queries:

1. create custom postgres function according to above documentation and your needs
2. it will be exposed by graphql API
3. use it