如何使用linq将数组添加到list <>

Question

I have the following problem: the query with linq works ok, but I need to add the coordinates within an array for each record that is repeated

Model

    public class AppPoisModel
    {
        public int idPoiType { get; set; }
        public string sector { get; set; }
        public double latPoint { get; set; }
        public double lngPoint { get; set; }
    }

Query

var result = (from c in db.coord
                      select new AppPoisModel
                      {
                          idPoiType = c.id,
                          sector = c.sector,
                          latPoint = c.latitude ?? 0,
                          lngPoint = c.longitude ?? 0
                      }).ToList();

Result

[
{
    "$id": "1",
    "sector" : "A",
    "latPoint": 0,
    "lngPoint": 0
},
{
    "$id": "2",
    "sector" : "A",
    "latPoint": 0,
    "lngPoint": 0
}
]

Desired result

[
{
    "$id": "1",
    "sector" : "A",
    "coords": [{latPoint, lngPoint}, {latPoint, lngPoint}]
}
]

thank you very much for your contributions

Answer 1

The initial query you suggested has no clue that there's a common relationship with items in the same sector.

To accomplish this, you'll want to use the Enumerable.GroupBy() method to group those items together with the basis of having the same id and sector together.

If both of those will always be correlated, you can just GroupBy() one of them to make the comparison simpler, but the results will also reflect that.

var result = (from c in db.coord
    select new AppPoisModel
    {
        idPoiType = c.id,
        sector = c.sector,
        latPoint = c.latitude ?? 0,
        lngPoint = c.longitude ?? 0
    }).GroupBy(x => new { id = x.idPoiType, sector = x.sector });

In your case, possibly with both id and sector . This will be your key when you want to loop over the results. So that you can morph the results into the data type you want.

Answer 2

looks like you need a group by...

Also you might create a class for Coords, and make AppPoisModel or a new result class, with a coords field typed as a collection of coords

check it out: Group by in LINQ similar solution https://stackoverflow.com/a/47580961