如何使用此 foreach 循环编写 linqu 查询

Question

This below is my code and I want to write a linq query for this three list (Dictionaryfilter,collectionfilter,reffrencefilter) this as are mmy list and want to add when item is selected then add into a SelectedIdList,Using Linq in c#

SelectedIdList = new List<long>();
foreach (var item in DictionariesFilter)
{
    if (item.IsSelected)
    {
        SelectedIdList.Add(item.DictionaryId);
    }
}

foreach (var item in CollectionsFilter)
{
    if (item.IsSelected)
    {
        SelectedIdList.Add(item.DictionaryId);
    }
}

foreach (var item in RefrencesFilter)
{
    if (item.IsSelected)
    {
        SelectedIdList.Add(item.DictionaryId);
    }                                                          
}

Answer 1

它可能看起来像：

SelectedIdList.AddRange(
    DictionariesFilter.Where(x=>x.IsSelected).Select(x=>(long)x.DictionaryId)
);
SelectedIdList.AddRange(
    CollectionsFilter.Where(x=>x.IsSelected).Select(x=>(long)x.DictionaryId)
);
SelectedIdList.AddRange(
    RefrencesFilter.Where(x=>x.IsSelected).Select(x=>(long)x.DictionaryId)
);

Answer 2

一种方法是简单地使用Where和Concat 。

SelectedIdList = DictionariesFilter.Where(x => x.IsSelected).Select(x => (long)x.DictionaryId)
    .Concat(CollectionsFilter.Where(x => x.IsSelected).Select(x => (long)x.DictionaryId))
    .Concat(RefrencesFilter.Where(x => x.IsSelected).Select(x => (long)x.DictionaryId))
    .ToList();

如果他们有一个共同的接口，它可以被简化。

public interface IFilter
{
    bool IsSelected { get; }
    long DictionaryId { get; }
}

SelectedIdList = DictionariesFilter
    .Concat(CollectionsFilter)
    .Concat(RefrencesFilter)
    .Where(x => x.IsSelected)
    .Select(x => x.DictionaryId)
    .ToList();

Answer 3

你可以这样做。

var results1 = from item in DictionariesFilter
                              where item.IsSelected
                              select item.DictionaryId;
     selectedList.Add(results1);

并且以类似的方式，您可以为循环的 rest 做。

Answer 4

如果可能，您可以尝试：

public interface IFilter
{
    bool IsSelected { get; }
    int DictionaryId { get; }
}

SelectedIdList = new IFilter[] { DictionariesFilter, CollectionsFilter, ReferencesFilter}
    .SelectMany(dic => dic.Where(x => x.IsSelected).Select(x = > (long)x.DictionaryId) )
    .ToList();