来自数据表的C＃LINQ查询

Question

I'm trying to implement a LINQ query on a search page we're working with. The data coming back from the initial query is laid out as follows:

ListID ListName TagId TagValue
1      Name1    1     Tag1
1      Name1    2     Tag2
2      Name2    3     Tag3

Basically the lists are search categories and the tags are search terms. What I'm trying to do is bring back this list, separate it into unique lists, and then display the related tags on the page.

I have the data loaded into a dataTable, now I'm trying to get the list names into my SearchCategories object:

public class SearchCategories
{
    public int SearchCategoryId { get; set; }

    public string SearchCategoryName { get; set; }

    public SearchTags searchTags { get; set; }

    public List<SearchTags> lstSearchTags= new List<SearchTags>();
}

and the SearchTag class:

public class SearchTags
{
    public int SearchTagId { get; set; }

    public string SearchTagValue { get; set; }
}

and then the tags into the object's related list.

Here's the code I'm working with:

dtLists.Load(reader);

var distinctValues = dtLists.AsEnumerable()
   .Select(row => new SearchCategories
   {
   SearchCategoryId = row.Field<int>("ListNameID"),
   SearchCategoryName = row.Field<string>("listName")
   })
   .Distinct();

Newer to LINQ but think this should be easier. Thanks in advance.

Answer 1

This will do the job:

var result = dtLists.AsEnumerable()
        .GroupBy(m => new
        {
            ListID = m.Field<int>("ListID"),
            ListName = m.Field<string>("ListName")
        }, m => m)
        .Select(m => new
        {
            m.Key.ListID,
            m.Key.ListName,
            Tags = m.Select(x => new { x.Field<int>("TagId"), x.Field<string>("TagValue") })
        });

Then of course you have to map to your type...

Answer 2

try something like the following, uses the GroupBy, Not sure what your SearchTags so replace x => new SearchTags(x) with how its constructed.

dtLists.AsEnumerable()
    .Select(row => new {
       SearchCategoryId = row.Field<int>("ListID "),
       SearchCategoryName = row.Field<string>("listName"),
       TagId = row.Field<int>("TagId"),
       TagValue = row.Field<string>("TagValue")
    })
    .GroupBy(x => x.SearchCategoryId)
    .Select(g => new SearchCategories() {
                SearchCategoryId  = g.Key,
                SearchCategoryName = g.First().SearchCategoryName,
                lstSubCategories = g.Select(x => new SearchTags(){ SearchTagId = x.TagId, SearchTagValue = x.TagValue}).ToList()
                }).ToList();

Answer 3

I am not clear how you want your output, based on which criteria, just ask if you want to be more precise.

void Main()
{
    var list = new List<Data>(){
                            new Data
                            {
                               ListId = 1,
                               ListName = "Name1",
                               TagId = 1,
                               TagValue = "Tag1"
                            },
                            new Data
                            {
                               ListId = 1,
                               ListName = "Name1",
                               TagId = 2,
                               TagValue = "Tag2"
                            },
                            new Data
                            {
                               ListId = 2,
                               ListName = "Name2",
                               TagId = 3,
                               TagValue = "Tag3"
                            }};

    //this is to group all SearchCategories by SearchCategoryName
    var res = list.Select(x => new SearchCategories
    {
       SearchCategoryId = x.ListId,
       SearchCategoryName = x.ListName
    }).GroupBy(x => x.SearchCategoryName);

    //to have just distinct categories one time
    var res2 = list.Select(x => new SearchCategories
    {
        SearchCategoryId = x.ListId,
        SearchCategoryName = x.ListName
    }).Distinct(new SearchCategoriesComparer());

    //display your data here based on a Key. The output should be Key=Name1  with two elements inside and the other one with one element Key=Name2
    res.Dump(); 

    //display your data here
    res2.Dump(); 

}

public class Data
{
    public int ListId   {get; set;}
    public string ListName { get; set; }
    public int TagId { get; set; }
    public string TagValue { get; set;}
}


public class SearchCategories
{
    public int SearchCategoryId { get; set; }

    public string SearchCategoryName { get; set; }

    public List<SearchTags> lstSubCategories = new List<SearchTags>();
}

public class SearchCategoriesComparer : IEqualityComparer<SearchCategories>
{
    public bool Equals(SearchCategories x, SearchCategories y)
    {
        return x.SearchCategoryName == y.SearchCategoryName;
    }

    public int GetHashCode(SearchCategories obj)
    {
        return obj.SearchCategoryName.GetHashCode();
    }
}


public class SearchTags
{
    public string Tag{ get; set;}
}

Answer 4

This should be fairly easy to do using GroupBy .

dtLists.AsEnumerable()
    .GroupBy(x => new { ListNameID = x.Field<int>("ListNameID"), ListName = x.Field<string>("ListName") })
    .Select(x => new SearchCategories()
    {
        SearchCategoryId = x.Key.ListNameID,
        SearchCategoryName = x.Key.ListName,
        lstSearchTags = x.Select(y => new SearchTags(){ SearchTagId = y.Field<int>("TagId"), SearchTagValue = y.Field<string>("TagValue") }).ToList()
    });