Linq : Select Different Object Left Join-CodePudding

I've tow contracts and one query I want to select one of them based on join result , without using where clause,

from a in pContext
     join c in vContext 
       on a.id equals c.id into av 
     from lav in av.DefaultIfEmpty()
if(lav != null )
{
   select new DTO1()
  {
   a.id,
   a.name,
   lav.description
  }
}
else
{
 select new DTO2()
 {
  a.id,
  a.name
 }
}

CodePudding user response：

EF Core translates LINQ "left join" to SQL left join and you do not need to handle nulls in this case, because it expects values from DbDataReader. Simple projection should work:

var query =
    from a in pContext
    join c in vContext on a.id equals c.id into av 
    from lav in av.DefaultIfEmpty()
    select new DTO1
    {
        a.id,
        a.name,
        lav.description
    };

CodePudding user response：

from a in pContext
     join c in vContext 
       on a.id equals c.id into av 
     from lav in av.DefaultIfEmpty()
  select new DTO()
  {
   id = a.id,
   name = a.name,
   description = lav != null ? lav.description : "No Specified"
  }

The solution is based on Svyatoslav Danyliv comment using ternary operator but with different condition to avoid the NullReferenceException.