Question

我有以下对象：

public class User {
  public Int32 Id { get; set; }
  public List<Language> Languages { get; set; }
  public List<Skill> Skills { get; set; }
}

public class Language {
  public Int32 Id { get; set; }
  public String Name { get; set; }
}

public class Skill {
  public Int32 Id { get; set; }
  public String Name { get; set; }
}

然后我有以下查询：

List<UserModel> models = context.Users.Select(x =>
  new UserModel {
    Id = x.Id,
    Names = ????
  }).ToList();

我需要服用：
1.第一种用户语言的名称（如果有的话） 2.前2个用户技能的名称（如果有）。

并将这些名称添加到UserModel.Names，其中UserModel为：

public class UserModel {
  public Int32 Id { get; set; }
  public List<String> Names { get; set; }
}

我如何在查询中执行此操作？

Answer 1

您可以使用Take和Concat。请尝试以下代码：

List<UserModel> models = context.Users.Select(x =>
  new UserModel {
    Id = x.Id,
    Names = x.Languages.Take(1).Select(y=>y.Name)
     .Concat(x.Skills.Take(2).Select(y => y.Name)).ToList()
  }).ToList();

Answer 2

 Func<User, IEnumerable<string>> getUserLanguageNames = user => user.Languages.Select(language => language.Name);
 Func<User, IEnumerable<string>> getUserSkillNames = user => user.Skills.Select(skill => skill.Name);
 List<UserModel> models = context.Users.Select(user => new UserModel { Id = user.Id, Names = getUserLanguageNames(user).Concat(getUserSkillNames(user)).ToList() }).ToList();

Answer 3

您可以使用拍摄和跳过：

var ListUserModel = context.Users.Select(u => new UserModel { Id = u.Id, Names 
= new List<string> { u.Languages.FirstOrDefault().ToString(), 
u.Skills.Take(1).ToString(), u.Skills.Skip(1).Take(1).ToString() } });

获取许多对象列表的属性

3 个答案: