Comparing two lists using linq to sql

Question

Say I have two lists:

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; }
}

How do you determine if:

At least one item in JobDesiredSkills is contained in CandidateSkills (matched on SkillId)
All items in JobDesiredSkills are contained in CandidateSkills

I tried this, but get this error: Unable to create a constant value of type Only primitive types ('such as Int32, String, and Guid') are supported in this context.

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

I also tried this, but Contains expects a JobDesiredSkill object, but c is a CandidateSkillObject.

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

Thanks

Brandon Moretz · Accepted Answer · 2011-07-12 16:05:51Z

7

There are two linq methods that fit your exact needs:

Edit:

You need to select a "Projection" of the "Ids" in the collection to get an enumerable collection of them, then you can use any / all on those (you can't compare complex types without an explicit comparison object).

Here is a trivial example, I hope it helps.

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

(Note: I also edited your question to update the sample classes used in this code, hope you don't mind.)

edited Jul 12, 2011 at 16:05

answered Jul 11, 2011 at 23:33

Brandon Moretz

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15 Comments

RPM1984 Over a year ago

You can't use All to test if all items from one sequence are in another - you can only use All to test is all items in a sequence match a given predicate. I could be wrong though - example usage of 2) in this scenario?

Jon Over a year ago

@RPM you just have to construct the right predicate - eg JobDesiredSkills.All(j => CandidateSkills.Contains(j))

Brandon Moretz Over a year ago

@RPM a.All( n => b.Contains( n ) ); ?

RPM1984 Over a year ago

Lol, i've been owned, forgot about contains. Nice. :)

Brandon Moretz Over a year ago

@RPM hah, we've all been there my friend.

|

virlan2004 · Accepted Answer · 2011-07-11 23:39:31Z

0

I don't have Visual Studio at handy right now but it should be something like:

1.

 JobDesiredSkills.Where(j=>CandidateSkills.Any(c=>c.SkillId == j.SkillId)==true).ToList().Count()>0

2.

 JobDesiredSkills.Where(j=>CandidateSkills.Where(c=>c.SkillId == j.SkillId).ToList().Count()>0).ToList().Count()==JobDesiredSkills.Count()

answered Jul 11, 2011 at 23:39

virlan2004

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1 Comment

Prabhu Over a year ago

This is actually what I tried originally, but I get this error: Unable to create a constant value of type 'JobDesiredSkill'. Only primitive types ('such as Int32, String, and Guid') are supported in this context.

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