確保記錄具有所有關係，而不是任何

Question

我有一個linqpad腳本我正在處理，它的工作原理，但問題是它使用.AsEnumerable()將集合調用到內存中。有一天可能會有成千上萬個，所以我想盡可能地推遲一切事情。

我想簡單地進行檢查，以確保如果我通過new long[] { 2, 4 }的功能，那麼任何經驗有都標識2和4將被退回。

以前，我只使用了.Contains()但這將返回經驗有要麼 2或4

有沒有更好的方式來寫這個代碼，以便它會返回一個IQueryable<Experience>而不是一個List<Experience>所以我不必將所有結果加載到內存中以執行字符串concat？

void Main() 
{ 
    var AllExperiences = new List<_Experience>(); 
    AllExperiences.Add(new _Experience { Id = 1, Name = "Experience 1" }); 
    AllExperiences.Add(new _Experience { Id = 2, Name = "Experience 2" }); 

    AllExperienceTags.Add(new _ExperienceTag { ExperienceId = 1, TagId = 2 }); 
    AllExperienceTags.Add(new _ExperienceTag { ExperienceId = 1, TagId = 4 }); 
    AllExperienceTags.Add(new _ExperienceTag { ExperienceId = 2, TagId = 2 }); 

    var experiences = FilterBySelectedTags(AllExperiences, new[] { 2, 4 }.ToList()); 

    experiences.Dump(); 
} 

public List<_ExperienceTag> AllExperienceTags = new List<UserQuery._ExperienceTag>(); 

// Define other methods and classes here 
public List<_Experience> FilterBySelectedTags(List<_Experience> experiences, List<int> selectedTagIds) 
{ 
    var filteredExperiencesTags = AllExperienceTags.Where(x => selectedTagIds.Contains(x.TagId)); 

    var obj = filteredExperiencesTags.OrderBy(x => x.TagId).GroupBy(x => x.ExperienceId).AsEnumerable().Select(x => new 
    { 
     ExperienceId = x.Key, 
     ExpTags = string.Join(", ", x.Select(y => y.TagId)) 
    }); 

    var filteredTags = obj.Where(x => x.ExpTags == string.Join(", ", selectedTagIds)); 

    // make sure all the selected tags are found in the experience, not just any 
    return experiences.Where(x => filteredTags.Select(y => y.ExperienceId).Contains(x.Id)).ToList(); 
} 

public class _Experience 
{ 
    public int Id { get; set; } 
    public string Name { get; set; } 
} 

public class _ExperienceTag 
{ 
    public int ExperienceId { get; set; } 
    public int TagId { get; set; } 
} 

Answer 1

Experience實體應該有一個導航屬性ExperienceTags：

public virtual ICollection<ExperienceTag> ExperienceTags{get;set;} 

如果是這樣的情況下，這應該工作：

var query= from e in Experiences 
      let experienceTagIds=e.ExperiencesTags.Select(et=>et.TagId) 
      where selectedTagIds.All(x=>experienceTagIds.Contains(x)) 
      select e; 

Answer 2

假設經驗，上有一個導航屬性標籤，那麼你可以這樣做：

void Main() 
{ 
    var experiences = Experiences.FilterBySelectedTags(new long[] { 2, 4 }); 

    experiences.Dump(); 
} 
public static class ExperienceExtensions { 
    public static IQueryable<Experience> FilterBySelectedTags(this IQueryable<Experience> experiences, IEnumerable<long> selectedTagIds) 
    { 
    return experiences.Where(e=>selectedTagIds.All(id=>e.Tags.Any(t=>t.TagId==id))); 
    } 
}