Query based on relation between fields values

Users GraphQL
1

Hello,

for the sake of simplicity let’s say i have a schema with 2D vectors.

type Vector
{
    id: ID!
    x: Float!
    y: Float!
}

I’m trying to come up with a simple query fetching vectors for which y > x. How do i do it ? Seems trivial but really i haven’t found any simple solution…

Thanks

1 Like
2

Hi @lumi
As far as I’m concerned there is not a clean and very efficient way to do that. One way is to use a Lambda Query:
In your schema use this:

type Vector {
  VectorID: ID!
  X: Int
  Y: Int
}

type Query {
   findXbiggerThanY(name: String): [Vector] @lambda
}

And in your Lambda Script add this function:

async function findXbiggerThanY({args, dql, graphql}) {
    let { data: { queryVector } } = await graphql(`
    {
        queryVector {
            VectorID
            X
            Y
        }
    }
    `);
    queryVector = queryVector.filter(({ X, Y })=> X > Y);
    return queryVector;
}

self.addGraphQLResolvers({
    "Query.findXbiggerThanY": findXbiggerThanY,
})

Now if you make this query you can get the results:

query MyQuery {
  findXbiggerThanY {
    VectorID
    X
    Y
  }
}

The better choice is to store the result when you are changing X or Y in another field(I know that if you want to do various math operations this would not be a good option).

If you decided to store extra information in your type using @lambdaOnMutate will be helpful to automate the calculations and store them.

1 Like
3

Thanks for response!

I did try your solution with Lambda Query but am getting this error:
Evaluation of custom field failed because external request returned an error: unexpected error with: 400 for field: findXbiggerThanY within type: Query.

Any ideas as to why it fails? or how to debug it ?

Thanks

4

If you are using dgraph cloud please add your schema and lambda function here maybe I can help.
Also the example I explained is still in this url you can give it a try:
https://green-pine.us-east-1.aws.cloud.dgraph.io/graphql

5

Thanks, i tried your url. It seems to work fine on your side. On my side, however, i get the error i mentioned. I actually locally am using the schema lambda and query that you posted so literally doing copy paste. I’m using dockers for dgraph and lambda server so issuing commands:

sudo docker run -it -p 8080:8080 dgraph/standalone:master
sudo docker run -it --rm -p 8686:8686 -v /path/to/script/myLmbd.js  -e DGRAPH_URL=http://localhost:8080 dgraph/dgraph-lambda

if any ideas as to what’s wrong, do let me know please. Thank you.

6

@lumi I have no idea. But I will setup Dgraph Lambda in one server in a day or two, After that I can test this solution and let you know :innocent: