How to upsert new record in Prisma without an ID?

I'm using Prisma (https://www.prisma.io) as ORM. I want to check for duplicates when store data and, if not exists, create a new record.

I thought I could do that with upsert method provided by Prisma and available in the generated client, but the where clause of that method only works with id (or @unique fields), but if the record doesn't exist, there isn't any id to provide.

I provide an example of the problem.

datamodel.prisma

type System {
  id: ID! @unique
  performances: [SystemPerformance!]! @relation(name: "PerformanceBySystem" onDelete: CASCADE)
  name: String! @unique
}

type SystemPerformance {
  id: ID! @unique
  system: System! @relation(name: "PerformanceBySystem")
  date: DateTime!
  perf1: Float
  perf2: Float
}

seed.js

const { prisma } = require('./generated/prisma-client');
async function main(){
  await prisma.createSystem({
    name: 's1',
  });
  await prisma.createSystem({
    name: 's2',
  });
  await prisma.createSystem({
    name: 's3',
  });
}
main();

After creation there is a database with three Systems without performances. I'm trying to insert a new SystemPerformance if there aren't any that have same date and same System. I have tried

const { prisma } = require('./prisma/generated/prisma-client');

const perf = await prisma.upsertSystemPerformance({
       where: {
         system: {name: 's1'},
         date: "2019-03-12T00:01:06.000Z"
       },
       update: {
         perf1: 13.45,
         perf2: 18.93
       },
       create: {
        system: {
            connect: { name: 's1' }
        },
        date: "2019-03-12T00:01:06.000Z",
        perf1: 13.45,
        perf2: 18.93
       }
})

But an exception is thrown:

UnhandledPromiseRejectionWarning: Error: Variable '$where' expected value of type 'SystemPerformanceWhereUniqueInput!' but got: {"system":{"name":'s1'},"date":"2019-03-12T00:01:06.000Z"}. Reason: 'system' Field 'system' is not defined in the input type 'SystemPerformanceWhereUniqueInput'

The only solution I have found is check for existence and then update or create, but I wanted to do it with upsert.

let check = await prisma.$exists.SystemPerformance({
            system: {name: 's1'},
            date: "2019-03-12T00:01:06.000Z"
        });
let perfo;
if (check){
  const sysPerf = await prisma.systemPerformances({where:{system: {name: 's1'}, date: "2019-03-12T00:01:06.000Z"}})
            .$fragment(`
            {
                id
            }
            `);
  perfo = await prisma.updateSystemPerformance({
    where: {id: sysPerf[0].id},
            data: {
              perf1: 13.45,
              perf2: 18.93
            }
   })
}
else {
  perfo = await prisma.createSystemPerformance({
    system: {
      connect: { name: 's1' }
    },
    date: "2019-03-12T00:01:06.000Z",
    perf1: 13.45,
    perf2: 18.93
  }
})

Is there a way to do that with upsert?

The fields in where need to be unique.

If you can make some field, let's say date @unique (date: DateTime! @unique), and use that for your where in the upsert, I think it would work (tested on my local)