如何檢查LINQ到SQL空值

Question

我想要使用以下LINQ到SQL查詢來獲得結果。但它並不適用於如果parentCategoryId爲空

public static IEnumerable<Category> GetChildren(this Table<Category> source, int? parentCategoryId) 
    { 
     var categories = from c in source where c.ParenCategoryId == parentCategoryId select c; 
     return categories; 
    } 

通過，但下面的作品，如果空直接用於地方parentCategoryId

的

public static IEnumerable<Category> GetChildren(this Table<Category> source, int? parentCategoryId) 
    { 
     var categories = from c in source where c.ParenCategoryId == null select c; 
     return categories; 
    } 

Answer 1

您可以使用object.Equals，它將匹配null值也。

public static IEnumerable<Category> GetChildren(this Table<Category> source, int? parentCategoryId) 
{ 
    var categories = from c in source 
        where object.Equals(c.ParenCategoryId, parentCategoryId) 
        select c; 
    return categories; 
} 

Answer 2

你可以嘗試以下

public static IEnumerable<Category> GetChildren(this Table<Category> source, int? parentCategoryId) 
{ 
    var categories = from c in source 
        where (parentCategoryId != null? c.ParenCategoryId == parentCategoryId : c.ParenCategoryId == null) 
        select c; 
    return categories; 
}