Flutter Dart 如何将两个对象列表合并为单个列表

下面的代码应该可以做到这一点.它使用Map，其中键是主键.值是list1和list2中的reduce(它甚至将list1和/或list2中的date个重复项合并).最后，我添加了一些断言来实际测试它是否有效.

这里还有DartPad to run it条在线信息.

class Object1 {
  final String date;
  final int day_data;
  const Object1({required this.date, required this.day_data});
}

class Object2 {
  final String date;
  final int night_data;
  const Object2({required this.date, required this.night_data});
}

class Object3 {
  final String date;
  final int? day_data;
  final int? night_data;
  const Object3({required this.date, this.day_data, this.night_data});
}

List<Object3> merge(List<Object1> obj1List, List<Object2> obj2List) {
  final map = <String, Object3>{};
  obj1List.forEach((obj1) =>
      map.update(
        obj1.date, 
        (obj3) => Object3(date: obj3.date, day_data: obj1.day_data, night_data: obj3.night_data),
        ifAbsent: () => Object3(date: obj1.date, day_data: obj1.day_data, night_data: null),
      ));
  
  obj2List.forEach((obj2) =>
      map.update(
        obj2.date, 
        (obj3) => Object3(date: obj3.date, day_data: obj3.day_data, night_data: obj2.night_data),
        ifAbsent: () => Object3(date: obj2.date, day_data: null, night_data: obj2.night_data),
      ));
  
  return map.values.toList()
    ..sort((a, b) => a.date.compareTo(b.date));
}


void main() {
//here is the list 1
  List<Object1> list1=[
  Object1(date:"1",day_data:12),
  Object1(date:"2",day_data:15),
  ];

  //here is the list 2
  List<Object2> list2=[
  Object2(date:"1",night_data:56),
  Object2(date:"3",night_data:80),
  ];

  List<Object3> actualList = merge(list1, list2);
  
  //expected output
  List<Object3> expectedList=[
  Object3(date:"1",day_data:12,night_data:56),
  Object3(date:"2",day_data:15,night_data:null),
  Object3(date:"3",day_data:null,night_data:80),
  ];
  
  print('Checking size...');  
  assert(actualList.length == expectedList.length);
  print('OK');
  
  print('Checking items...');
  actualList.asMap().forEach((i, actual) {
    final expected = expectedList[i];
    print('  Checking item $i...');
    assert(actual.date == expected.date);
    assert(actual.day_data == expected.day_data);
    assert(actual.night_data == expected.night_data);
    print('  OK');
  });
  print('OK');
}