Question

How does one select a specific object using query-expression style Linq?

private static ObservableCollection<Branch> _branches = new ObservableCollection<Branch>();
public static ObservableCollection<Branch> Branches
{
    get { return _branches; }
}

static void Main(string[] args) {
    _branches.Add(new Branch(0, "zero"));
    _branches.Add(new Branch(1, "one"));
    _branches.Add(new Branch(2, "two"));

    string toSelect="one";

    Branch theBranch = from i in Branches
                        let valueBranchName = i.branchName
                        where valueBranchName == toSelect
                        select i;

    Console.WriteLine(theBranch.branchId);

    Console.ReadLine();
} // end Main


public class Branch{
    public int branchId;
    public string branchName;

    public Branch(int branchId, string branchName){
        this.branchId=branchId;
        this.branchName=branchName;
    }

    public override string ToString(){
        return this.branchName;
    }
}

Returns the following error:

Error   1   Cannot implicitly convert type 'System.Collections.Generic.IEnumerable<ConsoleApplication1.Program.Branch>' to 'ConsoleApplication1.Program.Branch'. An explicit conversion exists (are you missing a cast?)    C:\Users\dotancohen\testSaveDatabase\ConsoleApplication1\ConsoleApplication1\Program.cs 35  12  ConsoleApplication1

However, explicitly casting like so:

    Branch theBranch = (Branch) from i in Branches
                        let valueBranchName = i.branchName
                        where valueBranchName == toSelect
                        select i;

Returns this error:

Unable to cast object of type 'WhereSelectEnumerableIterator`2[<>f__AnonymousType0`2[ConsoleApplication1.Program+Branch,System.String],ConsoleApplication1.Program+Branch]' to type 'Branch'.

Can Linq not return an object, or am I missing something obvious?

Thanks.

Answer 1

Your query returns a sequence of branches (there may be many branches that satisfy the predicate), if you want the first branch that has the name “one” (or null if there are none that match the requirement) then use:

Branch theBranch = this.Branches.FirstOrDefault(b => b.branchName == "one");

I would also avoid public fields and use properties instead:

public class Branch
{
    public int Id { get; set; }
    public string Name { get; set; }