Flutter数据映射插件simple_mapper的使用

Flutter数据映射插件simple_mapper的使用

介绍

simple_mapper 是一个用于简化不同类型对象之间映射的Flutter插件。通过配置表达式，它可以减少映射对象所需的代码量。本文将详细介绍如何使用 simple_mapper 进行对象映射，并提供一个完整的示例demo。

使用方法

简单的1对1映射

可以通过传递一个回调函数来添加映射配置，该回调函数接受源对象和映射器作为参数，并返回目标对象。

var mapper = Mapper()
  .addMap<CompanyB, CompanyA>((source, mapper) => CompanyB(
      id: source.id,
      name: source.name,
    ));

var companyA = CompanyA(
  id: 1,
  name: 'ABC',
);

var companyB = mapper.map<CompanyB, CompanyA>(companyA);

映射子对象

在回调函数中可以使用映射器来映射子对象。

var mapper = Mapper()
  .addMap<CompanyB, CompanyA>((source, mapper, [params]) => CompanyB(
    id: source.id,
    name: source.name,
    employees: source.employees
      ?.map((employee) => mapper.map<EmployeeB, EmployeeA>(employee))
      ?.toList(),
  ))
  .addMap<EmployeeB, EmployeeA>((source, mapper, [params]) => EmployeeB(
    id: source.id,
    name: source.name,
    startDate: source.startDate,
    timeEmployed: source.startDate == null || source.endDate == null ?
      null :
      source.endDate.difference(source.startDate),
    company: mapper.map<CompanyB, CompanyA>(source.company),
  ));

映射null

如果源对象为null，则不会执行回调函数，map 方法会直接返回null。

var company = mapper.map<CompanyB, CompanyA>(null);
print(company == null); // true

映射附加参数

在某些情况下，源对象可能不包含所有需要映射到目标对象的数据。这时可以传递附加参数。

var mapper = Mapper()
  .addMap<CompanyB, CompanyA>((source, mapper, [params]) => CompanyB(
    id: source.id,
    name: source.name,
    employees: source.employees
      ?.map((employee) => mapper.map<EmployeeB, EmployeeA>(employee, {
        'companyId': source.id,
      }))
      ?.toList(),
  ))
  .addMap<EmployeeB, EmployeeA>((source, mapper, [params]) => EmployeeB(
    id: source.id,
    companyId: params != null ? params['companyId'] : null,
    name: source.name,
    startDate: source.startDate,
    timeEmployed: source.startDate == null || source.endDate == null ?
      null :
      source.endDate.difference(source.startDate),
  ));

完整示例Demo

以下是一个完整的示例demo，展示了如何使用 simple_mapper 进行对象映射。

import 'package:simple_mapper/simple_mapper.dart';

// 定义模型类
class CompanyA {
  final int id;
  final String name;
  final List<EmployeeA>? employees;

  CompanyA({required this.id, required this.name, this.employees});

  [@override](/user/override)
  String toString() {
    return 'CompanyA{id: $id, name: $name, employees: $employees}';
  }
}

class CompanyB {
  final int id;
  final String name;
  final List<EmployeeB>? employees;

  CompanyB({required this.id, required this.name, this.employees});

  [@override](/user/override)
  String toString() {
    return 'CompanyB{id: $id, name: $name, employees: $employees}';
  }
}

class EmployeeA {
  final int id;
  final String name;
  final DateTime? startDate;
  final DateTime? endDate;

  EmployeeA({required this.id, required this.name, this.startDate, this.endDate});

  [@override](/user/override)
  String toString() {
    return 'EmployeeA{id: $id, name: $name, startDate: $startDate, endDate: $endDate}';
  }
}

class EmployeeB {
  final int id;
  final int companyId;
  final String name;
  final DateTime? startDate;
  final Duration? timeEmployed;

  EmployeeB({
    required this.id,
    required this.companyId,
    required this.name,
    this.startDate,
    this.timeEmployed,
  });

  [@override](/user/override)
  String toString() {
    return 'EmployeeB{id: $id, companyId: $companyId, name: $name, startDate: $startDate, timeEmployed: $timeEmployed}';
  }
}

void main() {
  var now = DateTime.now();
  var mapper = Mapper()
      .addMap<CompanyB, CompanyA>(
        (source, mapper, [params]) => CompanyB(
          id: source.id,
          name: source.name,

          // 使用映射器映射子对象
          employees: source.employees
              ?.map(
                (employee) => mapper.map<EmployeeB, EmployeeA>(employee, {
                  'companyId': source.id,
                }),
              )
              .toList(),
        ),
      )
      .addMap<EmployeeB, EmployeeA>(
        (source, mapper, [params]) => EmployeeB(
          id: source.id,

          // EmployeeA 没有 companyId，因此通过 params 传递
          companyId: params!['companyId'] ?? 0,
          name: source.name,
          startDate: source.startDate,
          timeEmployed: source.startDate == null || source.endDate == null
              ? null
              : source.endDate!.difference(source.startDate!),
        ),
      );

  var companyA = CompanyA(
    id: 1,
    name: 'ABC',
    employees: <EmployeeA>[
      EmployeeA(
        id: 1,
        name: 'John Smith',
        startDate: now.subtract(Duration(days: 30)),
        endDate: now,
      )
    ],
  );

  print('原始对象:');
  print(companyA);
  print('映射后:');
  print(mapper.map<CompanyB, CompanyA>(companyA));
}