LINQ Group结果并从另一个表中选择

Question

I have the following database structure:

table RoadSegment
    int SegmentID
    double StartKm
    double EndKm

table GeographicData
    double Km
    double latitude
    double longitude

table RoadFeature
    int FeatureID
    int SegmentID

And I want to select a list of all road features within a certain kilometer range, but i'd also like to get all of the geographic coordinates in each feature's segment. Is there anyway I can do this in just one database trip (a single LINQ statement)? I've tried the following:

from feat in RoadFeature
from geo in GeographicData
join seg in RoadSegment on feat.SegmentID equals seg.SegmentID

where geo.Km >= seg.StartKm && geo.Km <= seg.EndKm

group feat by feat.FeatureID into grp

select new {
    Feature = grp.Key,
    GeoData = grp.ToList()
}

But all I get is, for each feature, a list of features with the same ID. How can i proceed to get, for each feature, the list of coordinates on its segment ? That is, I'd like to have the following result out of the query:

[
    {
        FeatureID: 1,
        GeoData: [
            [-11.786783, 22.4567864],
            [-11.654684, 22.6546548],
            [-11.646648, 22.7867544]
        ]
    },

    {
        FeatureID: 2,
        GeoData: [
            [-11.111265, 22.4118787],
            [-11.568746, 22.6546548],
            [-11.124687, 22.0121571]
        ]
    }
]

Some data:

RoadSegment
    ID      StartKm     EndKm
    41      57.6        69.4
    42      69.4        80
    43      80          86.5
    44      86.5        92.2
    45      92.2        126
    46      126         132

RoadFeature
    FeatureID   SegmentID
    1           41
    2           42
    3           43
    4           44
    5           45
    6           46

GeographicData
    Km          latitude        longitude
    57.62       -19.959059      -44.339733          
    57.622      -19.959121      -44.339793          
    57.631      -19.959182      -44.339857          
    57.641      -19.959249      -44.339922          
    57.651      -19.959317      -44.339989          
    57.661      -19.959387      -44.340062          
    57.672      -19.959465      -44.340145          
    57.684      -19.959548      -44.340232          
    57.697      -19.959632      -44.340322          
    57.71       -19.959721      -44.340419          
    57.724      -19.959815      -44.340522          
    57.739      -19.959913      -44.34063           
    57.755      -19.960013      -44.340739          
    57.771      -19.960114      -44.340846          
    57.787      -19.960213      -44.34095    

(Point is, there is 1 feature per segment, but a WHOLE LOT of geo-data per kilometer. Also, i'd like solutions which don't rely on the uniqueness of feature per segment, if possible)

Answer 1

Think you just need to add geo in your grouping.

Then you can select these datas in your anonymous type.

So

from feat in RoadFeature
from geo in GeographicData
join seg in RoadSegment on feat.SegmentID equals seg.SegmentID

where geo.Km >= seg.StartKm && geo.Km <= seg.EndKm

group new {feat, geo} by feat.FeatureID into grp

select new {
    Feature = grp.Key,
    GeoData = grp.Select(x => x.geo).ToList()
}