P
Prisma•2mo ago
Nisharg Shah

Why I am getting typescript type error in my findOne function

export interface RoleService {
  findOne: <S extends NonNullable<RoleFindFirstArgs['select']>>(
    params: RequireAtLeastOne<Omit<NonNullable<RoleFindFirstArgs['where']>, 'type'>>,
    select: S,
  ) => Promise<Pick<RoleSchema, keyof S> | null>;
}


const findOne: RoleService['findOne'] = async (params, select) => {
  const data = await prismaClient.role.findFirst({
    where: {
      ...params,
      type: {
        in: userTypesOfNoDefaults,
      },
    },
    select,
  });

  return data;
};
export interface RoleService {
  findOne: <S extends NonNullable<RoleFindFirstArgs['select']>>(
    params: RequireAtLeastOne<Omit<NonNullable<RoleFindFirstArgs['where']>, 'type'>>,
    select: S,
  ) => Promise<Pick<RoleSchema, keyof S> | null>;
}


const findOne: RoleService['findOne'] = async (params, select) => {
  const data = await prismaClient.role.findFirst({
    where: {
      ...params,
      type: {
        in: userTypesOfNoDefaults,
      },
    },
    select,
  });

  return data;
};
Getting error in two places, in keyof S and in findOne function, but if I am doing same thing in other project its working fine but not in Prisma, am I doing wrong?
3 Replies
Prisma AI Help
Prisma AI Help•2mo ago
Skipping coffee for instant knowledge! Let's brew that AI answer now. The TypeScript type error you’re encountering in your findOne function is a common issue when wrapping Prisma Client methods and trying to preserve type safety for dynamic select arguments. This happens because TypeScript cannot infer the precise return type when select is passed as a generic parameter, especially if you type it as keyof S or similar. As a result, the return type often becomes {} or loses the correct shape, leading to type errors. Why does this happen? - When you use a generic S for select, TypeScript cannot automatically map the selected fields to the resulting object type. This is a known limitation and is discussed in several Prisma issues and discussions. If you type the return as Pick<RoleSchema, keyof S>, TypeScript expects S to be a record of keys, but Prisma’s select expects a shape like { field1: true, field2: true }, not a type with actual keys. - If you explicitly type the select parameter, TypeScript often widens the type, and Prisma’s internal type inference cannot narrow it down to the actual selected fields, resulting in {} or incorrect types in the return value. This is documented in this discussion and this issue. How to fix or work around: - Do not explicitly type the select parameter. Let TypeScript infer it from the object you pass. This allows Prisma’s type inference to work as intended. - If you need to type it, use function overloads or helper types like Prisma.UserGetPayload<{ select: S }> for the return type, as shown in this workaround: 
function findOne<S extends Prisma.RoleSelect>(
  params: Prisma.RoleWhereInput,
  select: S
): Promise<Prisma.RoleGetPayload<{ select: S }> | null> {
  return prismaClient.role.findFirst({ where: params, select });
}
function findOne<S extends Prisma.RoleSelect>(
  params: Prisma.RoleWhereInput,
  select: S
): Promise<Prisma.RoleGetPayload<{ select: S }> | null> {
  return prismaClient.role.findFirst({ where: params, select });
}
- Avoid using Pick<RoleSchema, keyof S> directly, as it does not m atch how Prisma’s types are generated. Summary:
This is a TypeScript limitation with dynamic generics and Prisma’s type inference. The recommended approach is to let TypeScript infer the select type or use Prisma’s GetPayload utility for accurate return types. This is not a Prisma bug, but a known TypeScript typing challenge with dynamic selects in Prisma wrappers source, source. 🤔 Alright, thanks for letting us know that there's still some help needed. A team member will reply to you shortly. In the meantime, please let us know any additional info, questions, or which parts of the answer may need clarification.
Nurul
Nurul•2mo ago
Did you try restarting the TypeScript server?
Nisharg Shah
Nisharg ShahOP•2mo ago
Yes tried, but not working

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