Linq多组加入C＃

Question

I need to create a structure like below.

• section1
  • question1
  • message1
• section2
  • quesiton2
  • message1
  • message2

I wrote the below code to generate this.

using System;
using System.Linq;
using System.Collections.Generic;


public class Program
{
    public static void Main()
    {
        // Question collection
        IList<Question> QuestionList = new List<Question>() { 
                new Question() { QuestionID = 1, QuestionName = "q1", SectionID = 1 } ,
                new Question() { QuestionID = 2, QuestionName = "q2",   SectionID = 1 } ,
                new Question() { QuestionID = 3, QuestionName = "q3",  SectionID = 2 } ,
                new Question() { QuestionID = 4, QuestionName = "q4" ,  SectionID = 2 } ,
                new Question() { QuestionID = 5, QuestionName = "q5"  } 
            };

        IList<Section> SectionList = new List<Section>() { 
                new Section(){ SectionID = 1, SectionName="Section 1"},
                new Section(){ SectionID = 2, SectionName="Section 2"},
                new Section(){ SectionID = 3, SectionName="Section 3"}
            };
        IList<Messages> MessagesList = new List<Messages>() { 
                new Messages(){ MessagesID = 1, MessagesName="Message 1",QuestionID=1},
                new Messages(){ MessagesID = 2, MessagesName="Message 2",QuestionID=1},
                new Messages(){ MessagesID = 3, MessagesName="Message 3",QuestionID=2}
            };
        var groupJoin = SectionList.GroupJoin(QuestionList,  //inner sequence
                                sct => sct.SectionID, //outerKeySelector 
                                s => s.SectionID,     //innerKeySelector

                                (sct, QuestionsGroup) => new // resultSelector 
                                {
                                    Questions = QuestionsGroup,

                                    SectionName = sct.SectionName
                                });

            var groupJoisn = QuestionList.GroupJoin(MessagesList,  //inner sequence
                                sct => sct.QuestionID, //outerKeySelector 
                                s =>s.QuestionID,     //innerKeySelector
                                (sct, QuestionsGroup) => new // resultSelector 
                                {
                                    Questions = QuestionsGroup,
                                    SectionName = sct.QuestionName
                                });



        foreach (var item in groupJoisn)
        { 
            Console.WriteLine(item.SectionName );

            foreach(var stud in item.Questions)
                Console.WriteLine(stud.MessagesName);
        }
        Console.WriteLine("-----------------");
        foreach (var item in groupJoin)
        { 
            Console.WriteLine(item.SectionName );

            foreach(var stud in item.Questions)
                Console.WriteLine(stud.QuestionName);
        }
    }

}

public class Question{

    public int QuestionID { get; set; }
    public string QuestionName { get; set; }
    public int SectionID { get; set; }
}
public class Messages{

    public int MessagesID { get; set; }
    public string MessagesName { get; set; }
    public int QuestionID { get; set; }
}
public class Section{

    public int SectionID { get; set; }
    public string SectionName { get; set; }
}

Unfortunately, i couldnt find a way to join the two group. because the section and questions connected using sectionid whereas questions and messages connected using questionid. When I using second group join im getting error questionid not exists in this context. how can i resolve this.

Answer 1

your creation structure should be changed but if you want a solution that keeps most of your creation structure you could use this

Note however using where in each question and each section is not good for performance. you should rather create the message list and the question list inside the creation of the section list.

IList<Messages> MessagesList = new List<Messages>() {
  new Messages(){ MessagesID = 1, MessagesName="Message 1",QuestionID=1},
  new Messages(){ MessagesID = 2, MessagesName="Message 2",QuestionID=1},
  new Messages(){ MessagesID = 3, MessagesName="Message 3",QuestionID=2}
};

// Question collection
IList<Question> QuestionList = new List<Question>() {
  new Question() { QuestionID = 1, QuestionName = "q1", SectionID = 1,messages = MessagesList.Where(message=> message.QuestionID==1).ToList() } ,
  new Question() { QuestionID = 2, QuestionName = "q2",   SectionID = 1,messages = MessagesList.Where(message=> message.QuestionID==2).ToList() } ,
  new Question() { QuestionID = 3, QuestionName = "q3",  SectionID = 2,messages = MessagesList.Where(message=> message.QuestionID==3).ToList() } ,
  new Question() { QuestionID = 4, QuestionName = "q4" ,  SectionID = 2 ,messages = MessagesList.Where(message=> message.QuestionID==4).ToList()} ,
  new Question() { QuestionID = 5, QuestionName = "q5" ,  SectionID = 2 ,messages = MessagesList.Where(message=> message.QuestionID==5).ToList() }
};  

IList<Section> SectionList = new List<Section>() {
  new Section(){ SectionID = 1, SectionName="Section 1",questions = QuestionList.Where(question=> question.SectionID == 1).ToList()},
  new Section(){ SectionID = 2, SectionName="Section 2",questions = QuestionList.Where(question=> question.SectionID == 2).ToList()},
  new Section(){ SectionID = 3, SectionName="Section 3",questions = QuestionList.Where(question=> question.SectionID == 3).ToList()}
};

foreach (var section in SectionList)
{
  Console.WriteLine("Section: " + section.SectionName);
  foreach (var question in section.questions)
  {
     Console.WriteLine("\tQuestion: " + question.QuestionName);
     foreach (var message in question.messages)
     {
        Console.WriteLine("\t\tMessage: " + message.MessagesName);
     }
  }
}

you will have to change your classes slightly for this.

public class Question
{

    public int QuestionID { get; set; }
    public string QuestionName { get; set; }
    public int SectionID { get; set; }

    public List<Messages> messages { get; set; }
}
public class Messages
{

    public int MessagesID { get; set; }
    public string MessagesName { get; set; }
    public int QuestionID { get; set; }
}
public class Section
{

    public int SectionID { get; set; }
    public string SectionName { get; set; }

    public List<Question> questions { get; set; }
}

Answer 2

Your request doesn't match with your objects, do you want in all sections a unique list combine Message and Question ?

Or if you want to have a tree like Section => Questions => Messages you can do it like this :

var group1 = SectionList.Select(section => new Section
{
    SectionID = section.SectionID,
    SectionName = section.SectionName,
    Questions = QuestionList.Where(question => question.SectionID.Equals(section.SectionID))
        .Select(question => new Question
        {
            QuestionID = question.QuestionID,
            QuestionName = question.QuestionName,
            SectionID = section.SectionID,
            Messages = MessagesList.Where(message => message.QuestionID.Equals(question.QuestionID))
                .Select(message => new Messages
                {
                    MessagesID = message.MessagesID,
                    MessagesName = message.MessagesName,
                    QuestionID = message.QuestionID
                })
        })
});

Of course you need to change a little bit your class :

public class Question
{

    public int QuestionID { get; set; }
    public string QuestionName { get; set; }
    public int SectionID { get; set; }
    public IEnumerable<Messages> Messages { get; set; }
}

public class Section
{

    public int SectionID { get; set; }
    public string SectionName { get; set; }
    public IEnumerable<Question> Questions { get; set; }
}

Answer 3

You can join QuestionList with MessagesList into QuestionMessagesList . After that, you need to join QuestionMessagesList with SectionList .

var questionMessages = QuestionList.GroupJoin(MessagesList,
                q => q.QuestionID,
                m => m.QuestionID,

                (Question, Messages) => new { Question, Messages }
            );

var groupJoin = SectionList.GroupJoin(questionMessages,
                sct => sct.SectionID,
                s => s.Question.SectionID,

                (sct, QuestionsGroup) => new
                {
                    Questions = QuestionsGroup,
                    SectionName = sct.SectionName
                });

Then:

            foreach (var item in groupJoin)
            {
                Console.WriteLine(item.SectionName);

                foreach (var stud in item.Questions)
                {
                    Console.WriteLine($" - {stud.Question.QuestionName}");

                    foreach (var message in stud.Messages)
                    {
                        Console.WriteLine($"  -- {message.MessagesName}");
                    }
                }
            }