LINQ to Objects Join two collections to set values in the first collection

Question

I have the following Entity Framework query:

var results = from r in db.Results               select r; 

I'm using AutoMapper to map to another type:

var mapped = Mapper.Map<IEnumerable<Database.Result>, IEnumerable<Objects.Result>>(results); 

In my Objects.Result type, I have a property called reason that is not coming from the database. It is coming from another source that I need to basically populate back into my mapped type:

var reasons = new List<Reason> {     new Reason { Id = 1, Reason = "asdf..." } }; 

I need to join the reasons with my mapped collection and set the Reason property in my mapped collection using the value from my reasons collection. Is this possible?

 // need something like this:  mapped = from m in mapped           join r in reasons on m.Id equals r.Id           update m.Reason = r.Reason           select m; 

Obviously the above code doesn't compile, but is there code I can write that does what I want?

Answer 1

Do the mutation in a loop. Optimally, Linq should be free of mutations to the collection(s) it operates against. Use Linq to filter, order, project your data, use traditional techniques to modify.

var joinedData = from m in mapped                   join r in reasons on m.Id equals r.Id                   select new { m, r };  foreach (var item in joinedData) {     item.m.Reason = item.r.Reason; } 

Answer 2

This may save lot of your time. Below code is for Join two collections and to set property value of first collection.

class SourceType {     public int Id;     public string Name;     public int Age { get; set; }     // other properties }  class DestinationType {     public int Id;     public string Name;     public int Age { get; set; }     // other properties }     List<SourceType> sourceList = new List<SourceType>();     sourceList.Add(new SourceType { Id = 1, Name = "1111", Age = 35});     sourceList.Add(new SourceType { Id = 2, Name = "2222", Age = 26});     sourceList.Add(new SourceType { Id = 3, Name = "3333", Age = 43});     sourceList.Add(new SourceType { Id = 5, Name = "5555", Age = 37});      List<DestinationType> destinationList = new List<DestinationType>();     destinationList.Add(new DestinationType { Id = 1, Name = null });     destinationList.Add(new DestinationType { Id = 2, Name = null });     destinationList.Add(new DestinationType { Id = 3, Name = null });     destinationList.Add(new DestinationType { Id = 4, Name = null });       var mapped= destinationList.Join(sourceList, d => d.Id, s => s.Id, (d, s) =>     {         d.Name = s.Name;         d.Age = s.Age;         return d;     }).ToList();