在Linq中将两个数据表作为父子表连接

Question

I need to build a typed list of parent-child objects that are read from two different Excel sources: One describes parent object, another describes child objects. The hierarchy is only 2 layers ever.
Reading into excel is not the issue, as it is read into 2 untyped datatables, but joining the information is.

The structure is very plain:
Parent has an ID and some text fields Children have a parentID (so its 1-m) and some text fields

The objects that these are to be populated into looks like this:

public class ParkingSites
{
    public List<ParkingLot> Lots { get; set; }

    public ParkingSites(List<ParkingLot> arg)
    {
        Lots = arg;
    }
}

public class ParkingLot
{
    public List<Bay> Bays{ get; set; }
    public int Id { get; set; }
    public List<string> ParkingLotDetails { get; set; } 
    public ParkingLot()
    {

    }
}

public class Bay
{
    public List<string> BayDetails { get; set; }
    public int ParentId { get; set; }    
    public Bay()
    {

    }
}

The excel sources have a fixed column order with the parent sheet's first column being the parentId, and the first column on the child sheet also being the parentId.

EDIT: After playing around a bit, I just made both parent and child classes typed, as the initial reason for leaving them mostly untyped lead to more problems than it prevented. This is part of a larger project where the untypedness is a better solution for our problem on the other classes with data that is not hierarchial.

Answer 1

You can simply group the list of children by the parent id, and then iterate over the parents and add each child that belongs to it.

For example, you could use ToLookup :

// assuming you have all Bay instances in a collection called bays
var baymap = bays.ToLookup(b => b.ParentId);

// and all ParkingLot instances in a collection called lots
foreach(var lot in lots)
    lot.Bays.AddRange(baymap[lot.Id]);

or, using the first element in the details lists:

var baymap = bays.ToLookup(b => b.BayDetails[0]);

foreach(var lot in lots)
    lot.Bays.AddRange(baymap[lot.ParkingLotDetails[0]]);

or, using Where without a lookup (probably slower, depends on your data):

foreach(var lot in lots)
    lot.Bays.AddRange(bays.Where(b => b.ParentId == lot.Id));