Typeorm Select

select.ts

import { Primitive, Simplify } from 'type-fest';
import {
  EntityManager,
  EntityTarget,
  FindOptionsOrder,
  FindOptionsRelations,
  FindOptionsWhere,
  ObjectLiteral,
} from 'typeorm';

export type Defined<T> = T extends undefined ? never : T;

declare const embeddedMarker: unique symbol;
export type Embedded<T = {}> = T & { [embeddedMarker]: true };
export const embed = <T extends {}>(x: T): Embedded<T> => x as Embedded<T>;

type NonRelationProperty = Primitive | Function | Date | Embedded;
export type Selection<Entity> = FindOptionsRelations<Entity>;

export type ShouldKeepProperty<
  Entity,
  Relations extends FindOptionsRelations<Entity>
> = keyof {
  [Property in keyof Entity as NonNullable<Entity[Property]> extends
    | NonRelationProperty
    | NonRelationProperty[]
    ? Property
    : Relations[Property] extends true | object
    ? Property
    : never]-?: unknown;
};

export type SelectProperty<
  Entity,
  Relations extends Selection<Entity>,
  Property extends keyof Entity
> = NonNullable<Entity[Property]> extends
  | NonRelationProperty
  | NonRelationProperty[]
  ? Defined<Entity[Property]>
  : NonNullable<Entity[Property]> extends (infer Relation)[]
  ? Relations[Property] extends true
    ? Select<Relation, {}>[]
    : Relations[Property] extends FindOptionsRelations<NonNullable<Relation>>
    ? Select<Relation, Relations[Property]>[]
    : unknown
  : Relations[Property] extends true
  ? Select<Defined<Entity[Property]>, {}>
  : Relations[Property] extends FindOptionsRelations<
      NonNullable<Defined<Entity[Property]>>
    >
  ? Select<Defined<Entity[Property]>, Relations[Property]>
  : unknown;

export type Select<
  Entity,
  Relations extends Selection<Entity> = {}
> = Simplify<{
  [Property in keyof Entity as Property extends ShouldKeepProperty<
    Entity,
    Relations
  >
    ? Property
    : never]-?: SelectProperty<Entity, Relations, Property>;
}>;

type Options<Entity, Relations extends FindOptionsRelations<Entity>> = {
  relations?: Relations;
  where?: FindOptionsWhere<Entity>;
  order?: FindOptionsOrder<Entity>;
};

export const select = async <
  Entity extends ObjectLiteral,
  Relations extends FindOptionsRelations<Entity> = {}
>(
  db: EntityManager,
  entity: EntityTarget<Entity>,
  options?: Options<Entity, Relations>
): Promise<Select<Entity, Relations>[]> =>
  db.find(entity, options ?? {}) as any;

export const selectOne = async <
  Entity extends ObjectLiteral,
  Relations extends FindOptionsRelations<Entity> = {}
>(
  db: EntityManager,
  entity: EntityTarget<Entity>,
  options?: Options<Entity, Relations>
): Promise<Select<Entity, Relations> | null> =>
  db.findOne(entity, options ?? {}) as any;

export const selectOneOrFail = async <
  Entity extends ObjectLiteral,
  Relations extends FindOptionsRelations<Entity> = {}
>(
  db: EntityManager,
  entity: EntityTarget<Entity>,
  options?: Options<Entity, Relations>
): Promise<Select<Entity, Relations>> =>
  db.findOneOrFail(entity, options ?? {}) as any;