Upsert in prisma without ID creates duplicate records (promise error?)

I need to insert records in a PG database from a json file with 500k records.

Since the file is huge I’m creating a Read Stream and using JSONStream.parse to send json objects over to pipe.

So far so good. This is not the problem, I’m just providing context.

After parsing the object, I need to insert the information using prisma but I cannot insert records if certain field is already in the table. So first thing I think is that I should use an upsert.

The problem is that this field is not a unique key of that table, therefore I cannot use it in the where clause of the prisma upsert.

Then, I did the following:

           await prisma.pets
                where: { name: nameFromJson },
              .then(async (existing_pet) => {
                if (!existing_pet) {
                  await prisma.pets.create({
                    data: {
                      name: nameFromJson,
                      legs: numberOfLegs,
                      isAlive: isAlive,
              .catch((error) => {
                throw new Error(error)

My idea is to find the record with the same field first and when that promise is resolved, send the result to another promise where I can check the record and if it does not exist, then just shoot the create.

But I keep getting duplicates in the table.

I’d like to understand what I’m doing wrong.