Using @FieldResolver

foo.entity.ts

@Entity()
@ObjectType()
export class Foo extends BaseEntity {
    @PrimaryGeneratedColumn('uuid')
    @Field(() => ID)
    id: string;

    @Column()
    @Field()
    title: string;
    
    // we create a special field that has no equivalent in the database
    @Field({ nullable: true })
    scheduledDate: Date;
}

foo.resolver.ts

// https://typegraphql.com/docs/resolvers.html#field-resolvers

@FieldResolver(() => Date)
async scheduledDate(@Root() foo: Foo): Promise<Date> {
    // Write the custom sql query you want with the gql root.
    return new Date();
}