I am trying to retrieve data from a postgresql database, transform it to a view model array and return the data to the client, ideally as a single object in this case rather than an array. I am getting the following error for the code I have listed beneath the error message. I am new to the functional programming space and am confused on how to utilize the data transformation concepts?

我正在尝试从PostgreSQL数据库检索数据，将其转换为视图模型数组，并将数据返回给客户端，在本例中最好是作为单个对象，而不是数组。对于我在错误消息下面列出的代码，我收到以下错误。我是函数式编程领域的新手，对如何利用数据转换概念感到困惑。

TS2345: Argument of type ‘(department: {}) => (department: QueryResult) => Department’ is not assignable to parameter of type '(a: {}) => TaskEither<DBError, {}>'.   Type ‘(department: QueryResult) => Department’ is not assignable to type 'TaskEither<DBError, {}>'.

TS2345：‘(Department：{})=>(Department：QueryResult)=>Department’的参数不能赋给‘(a：{})=>TaskEther ’类型的参数。‘TaskEither ’类型‘(Department：QueryResult)=>Department’不可赋值。

type DBError = MultipleResultsError | NoRecordsFoundError | Error;

const retrieveDepartments = async ({departmentId}: {departmentId: number}): Promise<TE.TaskEither<DBError, Department[]>> => {
    const client = await pool.connect();

    try {
        const query = 'SELECT * FROM department where departmentId = ?';
        const res: QueryResult<Department> = await client.query(query, [departmentId]);

        return pipe(
            TE.right(res.rows),
            TE.chain(
                TE.traverseArray(department => mapDepartmentViewModel)
            )
        );
    } catch (e) {
        return TE.left(e);
    } finally {
        client.release();
    }
}

export type Department = {
    departmentId: number,
    departmentName: string,
    departmentSupervisorId: number,
    departmentSupervisorFirstName: string,
    departmentSupervisorLastName: string
}

export const mapDepartmentViewModel = (department: QueryResult): Department => ({
    departmentId: department.departmentId,
    departmentName: department.departmentName,
    departmentSupervisorId: department.departmentSupervisorId,
    departmentSupervisorFirstName: department.departmentSupervisorFirstName,
    departmentSupervisorLastName: department.departmentSupervisorLastName
});

TaskEither<T, E> is just a type alias for Task<Either<T, E>>.

TaskEther 只是TASK >的类型别名。

Task<T> is a type alias for () => Promise<T>.

任务是()=>Promise 的类型别名。

retrieveDepartments actually returns a Promise<Either<DBError, Department[]>> since all the return values are Eithers. Therefore you should change its return type to Promise<Either<DBError, Department[]>>.

因为所有返回值都是Other，所以RetriveDepartments实际上返回了一个Promise >。因此，您应该将其返回类型更改为Promise< >。

Note that retrieveDepartments itself couldn't be typed as a TaskEither<DBError, Department[]> since it requires an argument, and Task take none: typed as a task, users won't be able to pass the arguments it actually expects.

请注意，receteDepartments本身不能被类型化为TaskEther ，因为它需要一个参数，而Task Take None：作为一个任务类型化，用户将无法传递它实际需要的参数。

type DBError = MultipleResultsError | NoRecordsFoundError | Error;

export type Department = {
    departmentId: number;
    departmentName: string;
    departmentSupervisorId: number;
    departmentSupervisorFirstName: string;
    departmentSupervisorLastName: string;
};

const retrieveDepartments = async ({
    departmentId,
}: { departmentId: number }): Promise<TE.TaskEither<DBError, Department[]>> => {
    const client = await pool.connect();

    try {
        const query = 'SELECT * FROM department where departmentId = ?';
        const res: QueryResult<Department> = await client.query(query, [departmentId]);

        return pipe(
            TE.right(res.rows),
            TE.chain((departments: Department[]) =>
                pipe(
                    TE.traverseArray(mapDepartmentViewModel)(departments),
                    TE.map((result: Department[]) => result)
                )
            )
        );
    } catch (e: DBError) {
        return TE.left(e);
    } finally {
        client.release();
    }
};

export const mapDepartmentViewModel = (
    department: QueryResult
): TE.TaskEither<DBError, Department> =>
    TE.tryCatch(
        () => {
            const mappedDepartment: Department = {
                departmentId: department.departmentId,
                departmentName: department.departmentName,
                departmentSupervisorId: department.departmentSupervisorId,
                departmentSupervisorFirstName: department.departmentSupervisorFirstName,
                departmentSupervisorLastName: department.departmentSupervisorLastName,
            };
            return mappedDepartment;
        },
        (error: DBError) => error
    );