如何在C＃中的字典上实现linq？

Question

I am facing a problem while creating online exam portal using linq on dictionary in C#. My concern is to get Online Exam category, SubCategory. I made a request to database server to fetch my data. Now my data is available at front end but I am trying to fetch record in a convenient way so that I can divide my data in Category, Subcategory and questions. for example I want my Headline and category to be like:-

General Knowledge

• Basic General Knowledge
• World Geography
• Inventions
• Honours and Awards

Maths

• Time & Speed
• Algebra
• Accounts

but with below given code my result is being displayed

General Knowledge

• Basic General Knowledge
• Basic General Knowledge
• Basic General Knowledge

this is getting repeated according to the number of question per subcategory.

Code I am using is

 public ActionResult getOnlineTestTitle()
    {
        List<GopreadyOnlineTest> search;
        if (Session["OnlineTest"] == null)
        {
             search= GopreadyOnlineTest.Search(WebConfigurationManager.ConnectionStrings["liveData"].ConnectionString).ToList();
             Session["OnlineTest"] = search;
        }
        else
        {
            search = (List<GopreadyOnlineTest>)Session["OnlineTest"];
        }            
        List<string> categoryName = search.Select(x => x.CategoryName).Distinct().ToList();
        Dictionary<string, List<GopreadyOnlineTest>> result2 = new Dictionary<string, List<GopreadyOnlineTest>>();
        foreach (string item in categoryName)
        {
            result2.Add(item, search.Where(s => s.CategoryName.ToUpper() == item.ToUpper()).ToList());
        }
        return Json(result2, JsonRequestBehavior.AllowGet);            
    }

Here is my proc which is returning me the data.

alter proc Quiz_SEARCH
(
    @CategoryName varchar(200) = null,
    @SubCategoryName varchar(200) = null
)
as
select c.catId as 'CategoryId', c.catName as 'CategoryName', s.subCatId as 'SubCategoryId', s.subCatName as 'SubCategoryName',
 q.question as 'Question', q.opta as 'OptionA',
q.optb as 'OptionB', q.optc as 'OptionC', q.optd as 'OptionD', q.answer, q.quesDescription as 'QuestionDescription'
from quizcategory c join quizsubcategory s on c.catid=s.catid
join quizquestion q on s.subcatid = q.subcatid
where 
(@CategoryName is null or [CatName]=@CategoryName)
and
(@subcategoryName is null or [SubCatName]=@SubCategoryName)

     ----------

Please help by solving this. If I put following line to solve the problem it is not allowing me to do this.

result2.Add(item, search.Where(s => s.CategoryName.ToUpper() == item.ToUpper()).Select(x=>x.SubCategoryName).Distinct().ToList());

Here is my jquery which is designing the page dynamically.

function GetOnlineTestTitle() {    
    $.ajax({
        type: "GET",
        url: "getOnlineTestTitle",
        contentType: "application/json; charset=utf-8",
        dataType: "json",
        async: true,
        cache: false,
        success: function (msg) { 
            var htmlString = '';
            alert(JSON.stringify(msg));
            $("#examList").html(htmlString);
            $.each(msg, function (key, val) {
                if (val.length != 0) {
                    htmlString += '<li><h3>' + key + '</h3></li>';
                }
                $.each(val, function (key2, val2) {
                    htmlString += '<li><a href="#"><b>'+val2.SubCategoryName+'</b></a></li>';
                });
            });
            $('#examList').append(htmlString);
        },
        error: function (msg) {
            alert("Error:" + JSON.stringify(msg));
        }
    });
}

Answer 1

You can use GroupBy method from LINQ to do that, see below.

Assuming that your GopreadyOnlineTest class is like that:

public class GopreadyOnlineTest
{
    public string CategoryId { get; set; }
    public string CategoryName { get; set; }
    public string SubCategoryId { get; set; }
    public string SubCategoryName { get; set; }
    public string Question { get; set; }
    public string OptionA { get; set; }
    public string OptionB { get; set; }
    public string OptionC { get; set; }
    public string OptionD { get; set; }
    public string QuestionDescription { get; set; }
}

And your List<GopreadyOnlineTest> search variable contains some data like that:

this.search = new List<GopreadyOnlineTest> 
{
    new GopreadyOnlineTest { CategoryName = "General Knowledge", SubCategoryName = "Basic General Knowledge" },
    new GopreadyOnlineTest { CategoryName = "General Knowledge", SubCategoryName = "World Geography" },
    new GopreadyOnlineTest { CategoryName = "General Knowledge", SubCategoryName = "Inventions" },
    new GopreadyOnlineTest { CategoryName = "General Knowledge", SubCategoryName = "Honours and Awards" },
    new GopreadyOnlineTest { CategoryName = "Maths", SubCategoryName = "Time & Speed" },
    new GopreadyOnlineTest { CategoryName = "Maths", SubCategoryName = "Algebra" },
    new GopreadyOnlineTest { CategoryName = "Maths", SubCategoryName = "Accounts" }
};

Lets create a ViewModel to hold our transformed data

public class SampleViewModel
{
    public string Category { get; set; }

    public List<string> SubCategories { get; set; }
}

Then your action should be like that:

[HttpGet]
public JsonResult GetOnlineTestTitle()
{               
    var result = search.GroupBy(x => x.CategoryName)
                       .Select(c => new SampleViewModel 
                                    { 
                                        Category = c.Key, 
                                        SubCategories = c.Select(sc => sc.SubCategoryName).Distinct().ToList() 
                                    });
    return Json(result, JsonRequestBehavior.AllowGet);
}

And in front end, your javascript should be like that:

function GetOnlineTestTitle() {    
    $.ajax({
        type: "GET",
        url: 'GetOnlineTestTitle',
        contentType: "application/json; charset=utf-8",
        dataType: "json",
        async: true,
        cache: false,
        success: function (msg) { 
            $("#examList").html("");
            var divs = msg.map(function (item) {
                var $div = $("<div>"); 
                var $ul = $("<ul>"); 
                var $h3 = $("<h3>").text(item.Category);

                item.SubCategories.forEach(function (itemSub) {
                    $ul.append($("<li>").text(itemSub));
                });
                $div.append($h3);
                $div.append($ul);
                return $div;
            });
            $('#examList').append(divs);
        },
        error: function (msg) {
            alert(JSON.stringify(msg));
        }
    });
}

You can see it working here: https://dotnetfiddle.net/PdaW67

Since the code above is more didatic, I am adding below almost real code for your case:

public ActionResult getOnlineTestTitle()
{
    var connectionString = WebConfigurationManager.ConnectionStrings["liveData"].ConnectionString;
    List<GopreadyOnlineTest> search = Session["OnlineTest"] as List<GopreadyOnlineTest> 
                                      ?? GopreadyOnlineTest.Search(connectionString).ToList();

    Session["OnlineTest"] = search;

    var result = search.GroupBy(x => x.CategoryName)
                       .Select(c => new SampleViewModel 
                                    { 
                                        Category = c.Key, 
                                        SubCategories = c.Select(sc => sc.SubCategoryName).Distinct().ToList() 
                                    });
    return Json(result, JsonRequestBehavior.AllowGet);            
}