The type 'T' cannot be assigned to type 'ObjectLiteral'

Question

The type 'T' cannot be assigned to type 'ObjectLiteral'

I am looking to implement the generic repository/service pattern in the following manner

import { EntityTarget, FindOptionsWhere } from "typeorm";

import { AppDataSource as db } from "../database";

export const getAllSerivce  = async <T>(
  entity: EntityTarget<T>,
  query?: FindOptionsWhere<T>
) => {
  const repository = db.getRepository(entity);
  const res = query ? await repository.findBy(query) : await repository.find();
  return res;
};

However, I am encountering this error:

Argument of type 'EntityTarget' is not assignable to parameter of type 'EntityTarget'. Type '{ type: T; name: string; }' is not assignable to type 'EntityTarget'. Type '{ type: T; name: string; }' is not assignable to type '{ type: ObjectLiteral; name: string; }'. Types of property 'type' are incompatible. Type 'T' is not assignable to type 'ObjectLiteral'.ts(2345) generic.service.ts(5, 38): This type parameter might need an extends ObjectLiteral constraint.

typescript express typeorm typescript-generics

Answer 1

Answer №1

When EntityTarget or FindOptionsWhere have a generic constraint on T, you must also include that constraint in your function:

export const fetchAllItems  = async <T extends ObjectLiteral>(
//                                   ^^^^^^^^^^^^^^^^^^^^^^^
  entity: EntityTarget<T>,
  query?: FindOptionsWhere<T>
) => {
  const repository = db.getRepository(entity);
  const result = query ? await repository.findBy(query) : await repository.find();
  return result;
};

Answer 2

When EntityTarget or FindOptionsWhere have a generic constraint on T, you must also include that constraint in your function:

export const fetchAllItems  = async <T extends ObjectLiteral>(
//                                   ^^^^^^^^^^^^^^^^^^^^^^^
  entity: EntityTarget<T>,
  query?: FindOptionsWhere<T>
) => {
  const repository = db.getRepository(entity);
  const result = query ? await repository.findBy(query) : await repository.find();
  return result;
};

The type 'T' cannot be assigned to type 'ObjectLiteral'

Answer №1

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