根据 Id 比较两个不同的列表

Question

我在这里要做的是尝试通过给定的 ID 从 CustomerFavoriteRepository 中查找文章。我有两个不同的列表 (articleList,customerFavList)，我正在比较两个列表的 ID 并将它们添加到空数组 (customFavartList)。有没有人帮助我如何使用 for 循环实现？我在循环中的“customFavartList.add()”处出现错误，我不知道我必须在那里给出哪个值。谢谢

void main() {
  final articleList = ArticleRepository().getArticleList();
  final customerFavList = CustomerFavoriteRepository().getCustomerFavorite();
  final List<NewCustomerFav> customFavartList = [];

  //this is what i tried 
  for (final articleId in articleList) {
    for (final customArticleId in customerFavList) {
      if (articleId.id == customArticleId.articleId) {
        customFavartList.add();
      }
    }
  }
}

class NewCustomerFav {
  final int id;
  final Article article;
  final int like;

  NewCustomerFav(this.id, this.article, this.like);
}

class ArticleRepository {
  final _articleList = [
    Article(1, 'burger'),
    Article(2, 'pizza'),
    Article(3, 'chicken'),
    Article(4, 'pasta'),
  ];

  List<Article> getArticleList() {
    return _articleList;
  }
}

class CustomerFavoriteRepository {
  final _customerFavoriteList = [
    CustomerFavorite(1, 1, 2),
    CustomerFavorite(2, 2, 2),
    CustomerFavorite(3, 3, 4),
  ];

  List<CustomerFavorite> getCustomerFavorite() {
    return _customerFavoriteList;
  }
}

class CustomerFavorite {
  final int id;
  final int articleId;
  final int like;

  CustomerFavorite(this.id, this.articleId, this.like);
}

class Article {
  final int id;
  final String name;

  Article(this.id, this.name);
}

Answer 1

您的问题的简单答案是您需要构建 NewCustomerFav，并将其传递给 add 方法：

//this is what i tried 
for (final article in articleList) {
  for (final customArticle in customerFavList) {
    if (article.id == customArticle.articleId) {
      // The values are just for example - I'm not certain how
      // you mean to derive `id` or `like` for a NewCustomerFav.
      final fav = NewCustomerFav(0, article, 1);
      customFavartList.add(fav);
    }
  }
}

另一方面，您的算法可以在此处进行改进 - 现在它将采用 n * m 次操作来构建 customFavartList，其中 n 是文章数，m 是收藏数量。

可以减少它，使算法在 n + m 的数量级上执行，相反，当有很多文章并且客户有很多收藏夹时，它会更好地扩展。

方法是从 favoritesList 创建一个 Set id，像这样：

// Assuming customerFavList is a list of int ids
final customerFavIdSet = Set.from(customerFavList.map((e) => e.articleId));

for (final article in articleList) {
  // Now you can check whether the article is a favorite with this one
  // query, rather than searching the whole list.
  if (customerFavIdSet.contains(article.id) {
    final fav = NewCustomerFav(0, article, 1);
    customFavartList.add(fav);
  }
}

根据 Id 比较两个不同的列表

Comparing two different Lists based on Ids

comparison

list

dart