使用linq到sql比较两个列表

Question

说我有两个清单:

List<CanidateSkill> canidateSkills;
List<JobDesiredSkill> desiredSkills;

class CanidateSkill
{
    public Guid CanidateId { get; set; }
    public Guid SkillId { get; set; }
}

class JobDesiredSkill
{
    public Guid JobId { get; set; }
    public Guid SkillId { get; set; }
}

你如何确定是否:

1. JobDesiredSkills中至少有一项包含在CandidateSkills中(在SkillId上匹配)

2. JobDesiredSkills中的所有项目都包含在CandidateSkills中

我尝试了这个,但是得到了这个错误:无法创建类型的常量值在此上下文中仅支持基本类型(例如Int32,String和Guid').

 return from candidate in _db.Candidates                           
 where (candidate.CandidateSkills.Any(c => job.JobDesiredSkills.Any(j => j.SkillId == c.SkillId))) 
 select candidate;

我也试过,但包含需要一个JobDesiredSkill对象,但c是CandidateSkillObject.

 return from candidate in _db.Candidates                           
 where CandidateSkills.Any(c => JobDesiredSkills.Contains(c)) 
 select candidate;

谢谢

Answer 1

有两种linq方法可满足您的确切需求:

1. IEnumerable.Any()
2. IEnumerable.All()

编辑:

您需要在集合中选择"Ids"的"投影"以获取它们的可枚举集合,然后您可以使用任何/所有(您无法在没有显式比较对象的情况下比较复杂类型).

这是一个简单的例子,我希望它有所帮助.

List<Guid> skills = 
    new List<Guid>( Enumerable.Range( 0, 20 ).Select( n => Guid.NewGuid() ) );

List<CanidateSkill> canidateSkills = new List<CanidateSkill>
(
    Enumerable.Range( 0, 10 ).Select( c => new CanidateSkill() { CanidateId = Guid.NewGuid(), SkillId = skills.ElementAt( c ) } )
);

List<JobDesiredSkill> desiredSkills = new List<JobDesiredSkill>
(
    Enumerable.Range( 5, 15 ).Select( d => new JobDesiredSkill() { JobId = Guid.NewGuid(), SkillId = skills.ElementAt( d ) } )
);

var anyDesiredSkills = canidateSkills.Any( c => desiredSkills.Select( ds => ds.SkillId ).Contains( c.SkillId ) ); // true
var allDesiredSkills = canidateSkills.All( c => desiredSkills.Select( ds => ds.SkillId ).Contains( c.SkillId ) ); // false

(注意:我也编辑了你的问题来更新这段代码中使用的示例类,希望你不介意.)