Question

I’ve had to use a lookup table in an EF project and it took me a bit of tinkering to get it working but I’m unsure how to query something.

If I have three tables (this is a test project to illustrate the question):

Person
------
ID - Int - PK
PersonName - varchar[50] 

and

Skill
-----
ID - Int - PK
SkillName - varchar[50]

which are linked by a lookup table:

PS_Lookup
---------
ID - Int - PK
PersonID - Int - FK : Person.ID
SkillID - Int - FK : Skill.ID

Now, if I want to return all users who have a skill of ID 1 I’ve worked out I can do:

var result = (from p in context.People                          
              select new
              {
                  PersonID = p.ID,
                  PersonName = p.PersonName,
                  FirstSkill = (from s in p.PS_Lookup 
                                where s.ID == 1
                                select s.SkillName),                              
              }).ToList();

My question is, what do I need to change on the above query just to return the PersonName and PersonID of everyone who has the skill with the ID 1?
i.e. Not returning “FirstSkill”. I don’t need the name as I know what FirstSkill is and I can’t see what I have to do with the where clause.

Answer 1

You need to use where condition in your query:

var result = (from p in context.People
              where p.PS_Lookup.Any(ps => ps.ID == 1)
              select new { p.ID, p.PersonName })
             .ToList();