Linq to Entities左外连接分组为一个集合

Question

from component in Materials.OfType<Container>().Where(m => m.Active)
join segmentFinanceRating in segmentFinanceRatingView on component.Id equals segmentFinanceRating.MaterialId into segmentFinanceRatingGroup
from segmentFinanceRatingWithDefault in segmentFinanceRatingGroup.DefaultIfEmpty()
select new
{
   id = component.Id,
   name = component.Name,
   subType = component.SubType,
   size = component.Size,
   MaterialIds = component.Materials.Select(x => x.Id),
   BrandNames = component.Brands.Select(x => x.Name),
   SegmentRatings = segmentFinanceRatingWithDefault
}

I have the above LINQ to Entities query that has a LEFT JOIN to get rating values for 1 or more segments for a given component.

The segmentFinanceRating entity has the properties, { MaterialId, SegmentId, Rating, LowRated }

At the moment the results are not grouped to the relevant component, ie the SegmentRatings property is not a single collection of segmentFinanceRating objects, instead I have multiple data rows with 1 segmentFinanceRating object in each.

I have seen some examples of using group x by y into z but I couldn't get it working, possibly due to some of the collections on the component that I need too, I'm not sure.

Any help would be appreciated on how to do this, thanks.

Answer 1

GroupBy in List doesn't work for you?

var list = (from component in Materials.OfType<Container>().Where(m => m.Active)
join segmentFinanceRating in segmentFinanceRatingView on component.Id equals segmentFinanceRating.MaterialId into segmentFinanceRatingGroup
from segmentFinanceRatingWithDefault in segmentFinanceRatingGroup.DefaultIfEmpty()
select new
{
   id = component.Id,
   name = component.Name,
   subType = component.SubType,
   size = component.Size,
   MaterialIds = component.Materials.Select(x => x.Id),
   BrandNames = component.Brands.Select(x => x.Name),
   SegmentRatings = segmentFinanceRatingWithDefault
}).ToList().GroupBy(s=> s.SegmentRatings);

Answer 2

In this case it's much easier to do the join in the anonymous type:

from component in Materials.OfType<Container>().Where(m => m.Active)
select new
{
   id = component.Id,
   name = component.Name,
   subType = component.SubType,
   size = component.Size,
   MaterialIds = component.Materials.Select(x => x.Id),
   BrandNames = component.Brands.Select(x => x.Name),
   SegmentRatings = (from segmentFinanceRating in segmentFinanceRatingView
                     where segmentFinanceRating.MaterialId == component.Id
                     select segmentFinanceRating)
}

You will have an empty collection of SegmentRatings when there are none for a specific component, giving the same effect as outer join.