How to pass anonymous types as parameters

Question

How can I pass anonymous types as parameters to other functions  Consider this example   var query   from employee in employees select new   Name   employee Name  Id   employee Id    LogEmployees query     The variable query here doesn t have strong type  How should I define my LogEmployees function to accept it   public void LogEmployees    list        foreach    item in list                   In other words  what should I use instead of   marks

User · Accepted Answer

I think you should make a class for this anonymous type. That'd be the most sensible thing to do in my opinion. But if you really don't want to, you could use dynamics:

public void LogEmployees (IEnumerable<dynamic> list)
{
    foreach (dynamic item in list)
    {
        string name = item.Name;
        int id = item.Id;
    }
}

Note that this is not strongly typed, so if, for example, Name changes to EmployeeName, you won't know there's a problem until runtime.

User · Answer

You can t pass an anonymous type to a non generic function  unless the parameter type is object   public void LogEmployees  object obj        var list   obj as IEnumerable         if  list    null         return       foreach  var item in list                   Anonymous types are intended for short term usage within a method   From MSDN - Anonymous Types      You cannot declare a field  a property  an event  or the return type of a method as having an anonymous type  Similarly  you cannot declare a formal parameter of a method  property  constructor  or indexer as having an anonymous type  To pass an anonymous type  or a collection that contains anonymous types  as an argument to a method  you can declare the parameter as type object  However  doing this defeats the purpose of strong typing     emphasis mine     Update  You can use generics to achieve what you want   public void LogEmployees lt T gt  IEnumerable lt T gt  list        foreach  T item in list

User · Answer

dynamic  can also be used for this purpose   var anonymousType   new   Id   1  Name    A      var anonymousTypes   new     new   Id   1  Name    A     new   Id   2  Name    B      private void DisplayAnonymousType dynamic anonymousType       private void DisplayAnonymousTypes IEnumerable lt dynamic gt  anonymousTypes       foreach  var info in anonymousTypes

User · Answer

Normally  you do this with generics  for example   MapEntToObj lt T gt  IQueryable lt T gt  query          The compiler should then infer the T when you call MapEntToObj query   Not quite sure what you want to do inside the method  so I can t tell whether this is useful    the problem is that inside MapEntToObj you still can t name the T - you can either    call other generic methods with T use reflection on T to do things   but other than that  it is quite hard to manipulate anonymous types - not least because they are immutable  -p  Another trick  when extracting data  is to also pass a selector - i e  something like   Foo lt TSource  TValue gt  IEnumerable lt TSource gt  source          Func lt TSource string gt  name        foreach TSource item in source  Console WriteLine name item          Foo query  x  gt x Title

User · Answer

I would use IEnumerable lt object gt  as type for the argument  However not a great gain for the unavoidable explicit cast  Cheers

User · Answer

Unfortunately  what you re trying to do is impossible   Under the hood  the query variable is typed to be an IEnumerable of an anonymous type  Anonymous type names cannot be represented in user code hence there is no way to make them an input parameter to a function  Your best bet is to create a type and use that as the return from the query and then pass it into the function   For example  struct Data     public string ColumnName      var query    from name in some Table             select new Data   ColumnName   name     MethodOp query       MethodOp IEnumerable lt Data gt  enumerable    In this case though  you are only selecting a single field  so it may be easier to just select the field directly   This will cause the query to be typed as an IEnumerable of the field type   In this case  column name  var query    from name in some Table select name       IEnumerable lt string gt

User · Answer

Instead of passing an anonymous type  pass a List of a dynamic type    var dynamicResult   anonymousQueryResult ToList lt dynamic gt     Method signature  DoSomething List lt dynamic gt   dynamicResult  Call method  DoSomething dynamicResult   done    Thanks to Petar Ivanov

User · Answer

You can do it like this   public void LogEmployees lt T gt  List lt T gt  list     Or IEnumerable lt T gt  list       foreach  T item in list                       but you won t get to do much with each item  You could call ToString  but you won t be able to use  say  Name and Id directly

User · Answer

If you know  that your results implements a certain interface you could use the interface as datatype   public void LogEmployees lt T gt  IEnumerable lt T gt  list        foreach  T item in list

User · Answer

You can use generics with the following trick  casting to anonymous type    public void LogEmployees lt T gt  IEnumerable lt T gt  list        foreach  T item in list                var typedItem   Cast item  new   Name       Id   0                now you can use typedItem Name  etc           static T Cast lt T gt  object obj  T type        return  T obj

[c#] How to pass anonymous types as parameters?

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