prisma: Type 'string' is not assignable to type 'never'

Question

This is my DTO

export class CreateGradeDto {
  id: string;
  first_bimester?: number;
  second_bimester?: number;
  third_bimester?: number;
  fourth_bimester?: number;
  studentId: never;
  classId: string;
  createdAt: Date;
  updatedAt: Date;
}

This is my prisma model

model Grades {
  id              String   @id @unique
  first_bimester  Float
  second_bimester Float
  third_bimester  Float
  fourth_bimester Float
  student         Student  @relation(fields: [studentId], references: [id])
  studentId       String   @unique
  class           Classes  @relation(fields: [classId], references: [id])
  classId         String   @unique
  createdAt       DateTime @default(now())
  updatedAt       DateTime @default(now())
}

And this is the student model

export class CreateStudentDto {
  id: string;
  name: string;
  cpf: string;
  createdAt: Date;
  updatedAt: Date;
}

(I'm using nestjs for this project)

i can't figure out why i can't save the grades, even knowing that all the time the id's are saved as string. I also checked the real postgre database and they are saved as strings.

Can someone help me??

user_4887407 · Answer

I couldn't initially figure out how to create a record and relate it to an existing record. I got the same error as you (well, number is not assignable to type never because my IDs are numeric).

Then I found the relevant part of the docs here: https://www.prisma.io/docs/concepts/components/prisma-client/relation-queries/#connect-an-existing-record - it's not entirely front and centre. The syntax in your case would be something like:

prisma.grade.create({
    data: {
      student: { connect: { id: 'your-student-id' } },
      // ... rest of the grade data
    },
  });

So, yes, you will need to do some sort of mapping to convert the relation fields in the DTO to the syntax above. Something like:

// Create a copy of the dto data without the foreign key fields. Using lodash here for brevity
const gradeData = _.omit(createGradeDto, ['studentId', 'classId']);

prisma.grade.create({
    data: {
      ...gradeData,
      student: { connect: { id: createGradeDto.studentId } },
      class: { connect: { id: createGradeDto.classId } },
    },
  });

prisma: Type 'string' is not assignable to type 'never'

1 Answers