linq query to create new objects

Question

assumed i have a class hierarchy where basically every class consists of a property item (like string) and a property list item of the nested class:

public class Master { public String myName; public List<Detail> myDetails; } public class Detail { public String myDetailDescription; public List<DetailParts> parts; } public class DetailParts { public int PartNumber; public String PartDescription; }

Now i would like to have a linq query that gives me an list of objects that consists of these elements

public class Result
{
    public String myName; // from Master
    public String myDetailDescription; // from Detail
    public int PartNumber; // from DetailParts
}

It is a silly question, I know, but i cant find useful links...

[Edit #1]: Better code sample:

public class Master
{ 
    public String myName;
    public List<Detail> myDetails = new List<Detail>();
}
public class Detail
{ 
    public String myDetailDescription;
    public List<DetailParts> parts = new List<DetailParts>();
}
public class DetailParts
{
    public int PartNumber;
    public String PartDescription;
}


// List of Masters
List<Master> master = new List<Master>();
// Two detail parts for the Details
DetailParts dp1 = new DetailParts { PartDescription = "dp1" };
DetailParts dp2 = new DetailParts { PartDescription = "dp2" };
// once again two details for the Master
Detail d1 = new Detail { myDetailDescription = "d1" };
Detail d2 = new Detail{ myDetailDescription = "d2"};
// Assign the Parts
d1.parts.Add(dp1);
d1.parts.Add(dp2);
d2.parts.Add(dp1);
d2.parts.Add(dp2);
Master m1 = new Master { myName = "m1" };
Master m2 = new Master { myName = "m2" };
m1.myDetails.Add(d1);
m1.myDetails.Add(d2);
m2.myDetails.Add(d1);
m2.myDetails.Add(d2);
master.Add(m1);
master.Add(m2);

// given a value for `myName` and `myDetailDescription` i  
// would be able to get a list with the `DetailParts` objects:

var t = master.Where(a => a.myName == "m2")
    .Select(a => a.myDetails).FirstOrDefault()
    .Where(b => b.myDetailDescription == "d1")
    .Select(c => c.parts).FirstOrDefault();

Tim Schmelter · Accepted Answer · 2016-05-04 07:50:09Z

4

You are looking for SelectMany:

List<Result> results = masterList
    .SelectMany(m => m.myDetails
        .SelectMany(d => d.parts
            .Select(dp => new Result
            {
                PartNumber = dp.PartNumber,
                myDetailDescription = d.myDetailDescription,
                myName = m.myName
            })))
    .ToList();

A more readable version with LINQ's query syntax:

var resultQuery = from m in masterList
                  from d in m.myDetails
                  from dp in d.parts
                  select new Result
                  {
                    PartNumber = dp.PartNumber,
                    myDetailDescription = d.myDetailDescription,
                    myName = m.myName
                  };
List<Result> results = resultQuery.ToList();

answered May 4, 2016 at 7:50

Tim Schmelter

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2 Comments

Wolfgang Roth Over a year ago

Whoha... you are quite fast :-) Will try this with my real class space.

Wolfgang Roth Over a year ago

I tried this with my classes and it worked - even though I forgot to mention, that i need some where clauses ;-)

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