我假设有一个简单的LINQ查询来做到这一点,我只是不太确定如何。

给定这段代码:

class Program
{
    static void Main(string[] args)
    {
        List<Person> peopleList1 = new List<Person>();
        peopleList1.Add(new Person() { ID = 1 });
        peopleList1.Add(new Person() { ID = 2 });
        peopleList1.Add(new Person() { ID = 3 });

        List<Person> peopleList2 = new List<Person>();
        peopleList2.Add(new Person() { ID = 1 });
        peopleList2.Add(new Person() { ID = 2 });
        peopleList2.Add(new Person() { ID = 3 });
        peopleList2.Add(new Person() { ID = 4 });
        peopleList2.Add(new Person() { ID = 5 });
    }
}

class Person
{
    public int ID { get; set; }
}

我想执行一个LINQ查询,给我所有人在peopleList2不在peopleList1。

这个例子应该给我两个人(ID = 4 & ID = 5)


当前回答

Klaus的回答很好,但是ReSharper会让你“简化LINQ表达式”:

var result = peopleList2。Where(p => peopleList1.)p2 => p2。= p.ID));

其他回答

由于迄今为止所有的解决方案都使用了流畅的语法,这里有一个查询表达式语法的解决方案,如果你感兴趣的话:

var peopleDifference = 
  from person2 in peopleList2
  where !(
      from person1 in peopleList1 
      select person1.ID
    ).Contains(person2.ID)
  select person2;

我认为它与给出的答案有很大的不同,有些人对此很感兴趣,甚至认为它很可能不是list的最佳选择。现在对于索引id的表,这肯定是可行的方法。

下面是一个实际的例子,它能让你掌握求职者不具备的IT技能 已经有了。

//Get a list of skills from the Skill table
IEnumerable<Skill> skillenum = skillrepository.Skill;
//Get a list of skills the candidate has                   
IEnumerable<CandSkill> candskillenum = candskillrepository.CandSkill
       .Where(p => p.Candidate_ID == Candidate_ID);             
//Using the enum lists with LINQ filter out the skills not in the candidate skill list
IEnumerable<Skill> skillenumresult = skillenum.Where(p => !candskillenum.Any(p2 => p2.Skill_ID == p.Skill_ID));
//Assign the selectable list to a viewBag
ViewBag.SelSkills = new SelectList(skillenumresult, "Skill_ID", "Skill_Name", 1);

一旦你写了一个通用的FuncEqualityComparer,你就可以在任何地方使用它。

peopleList2.Except(peopleList1, new FuncEqualityComparer<Person>((p, q) => p.ID == q.ID));

public class FuncEqualityComparer<T> : IEqualityComparer<T>
{
    private readonly Func<T, T, bool> comparer;
    private readonly Func<T, int> hash;

    public FuncEqualityComparer(Func<T, T, bool> comparer)
    {
        this.comparer = comparer;
        if (typeof(T).GetMethod(nameof(object.GetHashCode)).DeclaringType == typeof(object))
            hash = (_) => 0;
        else
            hash = t => t.GetHashCode(); 
    }

    public bool Equals(T x, T y) => comparer(x, y);
    public int GetHashCode(T obj) => hash(obj);
}

有点晚了,但一个很好的解决方案,也是Linq到SQL兼容的是:

List<string> list1 = new List<string>() { "1", "2", "3" };
List<string> list2 = new List<string>() { "2", "4" };

List<string> inList1ButNotList2 = (from o in list1
                                   join p in list2 on o equals p into t
                                   from od in t.DefaultIfEmpty()
                                   where od == null
                                   select o).ToList<string>();

List<string> inList2ButNotList1 = (from o in list2
                                   join p in list1 on o equals p into t
                                   from od in t.DefaultIfEmpty()
                                   where od == null
                                   select o).ToList<string>();

List<string> inBoth = (from o in list1
                       join p in list2 on o equals p into t
                       from od in t.DefaultIfEmpty()
                       where od != null
                       select od).ToList<string>();

向http://www.dotnet-tricks.com/Tutorial/linq/UXPF181012-SQL-Joins-with-C致敬

首先,从where条件的集合中提取id

List<int> indexes_Yes = this.Contenido.Where(x => x.key == 'TEST').Select(x => x.Id).ToList();

其次,使用“compare”语句来选择与所选内容不同的id

List<int> indexes_No = this.Contenido.Where(x => !indexes_Yes.Contains(x.Id)).Select(x => x.Id).ToList();

显然,您可以使用x.key != "TEST",但这只是一个示例