How to use a dictionary property in C# using LINQ

Question

While I userstand how get; & set; with simple types such as strings now can more properties like Dictionary be get or set or can they?

I have a small dos programe trying to do this. snippet below.

# User.cs
namespace LDIFMod
{
    public class User
    {

        public string UserHash { get; set; }
        public string UserID { get; set; }
        public Dictionary<string, string> UserDict { get; set; }  <- how to do this???
}

}

and in my Program.cs

var query = from line in File.ReadAllLines(args[0])
let UserRecord = line.Split(',')
select new User()

{

 UserHash = UserRecord[2].Trim() +UserRecord[3].Trim(),
 UserID = UserRecord[4].Trim(),
 UserDict.????   // userDict should contain key = UserRecord[5] & value = UserRecord[9]

}

Answer 1

You can use the collection initializer to create the dictionary:

{
    UserHash = UserRecord[2].Trim() +UserRecord[3].Trim(),
    UserID = UserRecord[4].Trim(),
    UserDict = new Dictionary<string, string> { { UserRecord[5],  UserRecord[9] } }
}

Also, see here: http://msdn.microsoft.com/en-us/library/bb531208.aspx

Answer 2

You will need to first initialize the dictionary in the constructor of the user class. Use the private set to prevent people from re-initializing the dictionary.

# User.cs
namespace LDIFMod
{
    public class User
    {
        User()
        {
            UserDict = new Dictionary<string, string>()
        }
        public string UserHash { get; set; }
        public string UserID { get; set; }
        public Dictionary<string, string> UserDict { get; private set; }
    }
}

Your calling code becomes

var query = from line in File.ReadAllLines(args[0])
let UserRecord = line.Split(',')
select new User()
{
     UserHash = UserRecord[2].Trim() +UserRecord[3].Trim(),
     UserID = UserRecord[4].Trim(),
     UserDict.Add(UserRecord[5],UserRecord[9]);
}

This returns one dictionary per query row. if you want all of the rows to share a dictionary you will need to make it static or not store it inside User. If you do this be aware that linq is delayed execution so the dictionary will not be fully populated until after you fully enumerate the query.

---

I thought I would give a example of how to do it with all of them in a single dictionary.

# User.cs
namespace LDIFMod
{
    public class User
    {
        public string UserHash { get; set; }
        public string UserID { get; set; }
        public readonly string[] SourceData {get; private set;}
    }
}

and here is the query

var query = from line in File.ReadAllLines(args[0])
let UserRecord = line.Split(',')
select new User()
{   
     UserHash = UserRecord[2].Trim() + UserRecord[3].Trim(),
     UserID = UserRecord[4].Trim(),
     SourceData = UserRecord;
}
var UserLookp = query.ToDictionary((user) => user.SourceData[5], (user) => user.SourceData[9]);

This is purely from memory without a ide to check for bugs so there could be some errors.