C＃泛型列表作为函数参数

Question

I am retrieving a list from a table in database:

var dependency = (from ctf in dc.Fields
                  join ctfd in dc.FieldsDependencies on ctf.id equals ctfd.Fieldid_depend
                  where ctf.ctid == ctid && ctf.fieldname == fieldname
                  select ctfd).ToList();

I am passing this list as parameter in another function:

public void DoYesDeleteDepField<T>(string fieldname, List<T> dep)

How I can change it so I can retrieve the id field?

But I cant iterate through the list and get the depsingle.id field.

foreach (var depsingle in dep)
        { var depsingleid = depsingle.id //ERROR
.....

Answer 1

您需要定义什么是T .. public void ...其中T：IHasId或在类级别定义它

Answer 2

It doesn't know that the <T> has the parameter .id so either cast it (like this var a = (int)something or var a = something as int ), or write it to something less generic from the List<t> . eg List<classname> .

Answer 3

As T can be anything from int to MyClass there´s no member called id on all those types. Thus you need a generic constraint that tells the compiler what types are possible for T , eg:

public void DoYesDeleteDepField<T>(string fieldname, List<T> dep) where T: MyClass

or omit generics completely as only one type is possible making the term generic quite useless. Simply define a class that hilds the values from your join and pass this to your method:

class MyClass
{
    public string Id { get; set; }
    // further properties
}

Now create instances of those objects from your query:

var result = (from ctf in dc.Fields
              join ctfd in dc.FieldsDependencies on ctf.id equals ctfd.Fieldid_depend
              where ctf.ctid == ctid && ctf.fieldname == fieldname
              select new MyClass 
              { 
                  id = ctf.id,
                  // further properties
              }).ToList();

public void DoYesDeleteDepField(string fieldname, List<MyClass> dep)