CODEWITHSUNDEEP
c#.netlinqjoin
jdruid
jdruid

Reputation: 613

.NET Linq Left Join

I have 2 tables in SQL:

Table 1 
Step Id
Step Name

Table 2
Profile Id
Step Id
Completed

I would like to return the following results even if there is not match in table 2:

Results
Table1.Step Id
Table1.Step Name
Table2.Profile Id
Table2.Completed

The way I am doing this in SQL is the following:

select * from [Table 1] t1
left join [Table 2] t2
on t1.Step Id = t2.Step Id

This produces the results I expect.

When I translate this into linq:

public static List<UserCompletion> GetStepCompletion(string category, string profileid) { 

List<Step> step = GetSteps(category);
List<UserStep> userStep = GetUserSteps(category, profileId);    

var q = from s in step
         join us in userStep
         on s.Id equals us.StepId
         select new UserCompletion
         {
           StepId = s.Id,
           Headline = s.StepName,
           ProfileId = us.ProfileId
           Completed= us.Completed
          };

     return q.ToList();

}

It works but like a JOIN not a left join. I only get matching results back.

Also, UserCompletion is an object that I return from this method.

Upvotes: 4

Views: 4377

Answers (3)

jdruid
jdruid

Reputation: 613

Found it.

Seems like I need to add a evaluation on the item that "may" be null.

I added the following to my select

Completed = (x == null) ? String.Empty : x.Completed

Upvotes: 0

jrummell
jrummell

Reputation: 43117

You could also try this (assuming us.Completed is boolean):

var q = from s in step
         let us = (from i in userStep where s.Id = i.StepId).SingleOrDefault()
         select new UserCompletion
         {
           StepId = s.Id,
           Headline = s.StepName,
           ProfileId = us.ProfileId
           Completed = us == null ? false : us.Completed
          };

This won't turn into a join in sql, but a nested select statement something like this:

select 
    StepId, Headline, ProfileId,
    isnull((select top(1) Completed from userStep where StepId = Id), 0) as Completed
from step

Upvotes: 5

Jakob Christensen
Jakob Christensen

Reputation: 14956

Try something along the lines of the following:

var q = from s in step
        join us in userStep 
        on s.Id equals us.StepId into tmpjoin
        from x in tmpjoin.DefaultIfEmpty()
        select new UserCompletion { ... }

Upvotes: 3

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