Flatten LINQ collection object with nested object collections - linq

Question

This is a tricky one. I an trying to flatten a LINQ object collection. Each item in the collection has the potential of having two collections of other objects. See the example below.
public class DemoClass
{
public string Name {get; set;}
public string Address {get; set;}
public List<Foo> Foos = new List<Foo>();
public List<Bar> Bars = new List<Bars>();
}
What I had been doing is this using this code block to flatten this object
var output = from d in DemoClassCollection
from f in d.Foos
from b in d.Bars
select new {
d.Name,
d.Address,
f.FooField1,
f.FooField2,
b.BarField1,
b.BarField2
};
But the problem I'm having is that the result I get is only those DemoClass objects that have objects in the Foos and Bars collections. I need to get all objects in the DemoClass regardless if there are objects in the Foos and Bars collections.
Any help would be greatly appreciated.
Thanks!

Answer 1

Sounds like you might want to use DefaultIfEmpty:
var output = from d in DemoClassCollection
from f in d.Foos.DefaultIfEmpty()
from b in d.Bars.DefaultIfEmpty()
select new {
d.Name,
d.Address,
FooField1 = f == null ? null : f.FooField1,
FooField2 = f == null ? null : f.FooField2,
BarField1 = b == null ? null : b.BarField1,
BarField2 = b == null ? null : b.BarField2
};

Answer 2

Looks like a left outer join in Linq will work (http://msdn.microsoft.com/en-us/library/bb397895.aspx
var output = from d in DemoClassCollection
from f in d.Foos.DefaultIfEmpty()
from b in d.Bars.DefaultIfEmpty()
select new {
d.Name,
d.Address,
f.FooField1,
f.FooField2,
b.BarField1,
b.BarField2
};

Answer 3

I believe you can implement an IComparer to perform custom JOINS or UNIONS in linq based on how you implement the CompareTo() method
From MSDN: http://msdn.microsoft.com/en-us/library/system.icomparable.aspx
using System;
using System.Collections;
public class Temperature : IComparable
{
// The temperature value
protected double temperatureF;
public int CompareTo(object obj) {
if (obj == null) return 1;
Temperature otherTemperature = obj as Temperature;
if (otherTemperature != null)
return this.temperatureF.CompareTo(otherTemperature.temperatureF);
else
throw new ArgumentException("Object is not a Temperature");
}
public double Fahrenheit
{
get
{
return this.temperatureF;
}
set {
this.temperatureF = value;
}
}
public double Celsius
{
get
{
return (this.temperatureF - 32) * (5.0/9);
}
set
{
this.temperatureF = (value * 9.0/5) + 32;
}
}
}
public class CompareTemperatures
{
public static void Main()
{
ArrayList temperatures = new ArrayList();
// Initialize random number generator.
Random rnd = new Random();
// Generate 10 temperatures between 0 and 100 randomly.
for (int ctr = 1; ctr <= 10; ctr++)
{
int degrees = rnd.Next(0, 100);
Temperature temp = new Temperature();
temp.Fahrenheit = degrees;
temperatures.Add(temp);
}
// Sort ArrayList.
temperatures.Sort();
foreach (Temperature temp in temperatures)
Console.WriteLine(temp.Fahrenheit);
}
}
// The example displays the following output to the console (individual
// values may vary because they are randomly generated):
// 2
// 7
// 16
// 17
// 31
// 37
// 58
// 66
// 72
// 95