Is it possible to cast a variable of type: dictionary<int, models.user> to dictionary<int, object> i

[Chavdar Kostov]

Is it possible to cast a variable of type: dictionary<int, models.user> to dictionary<int, object> in C#?

 

Hi, everyone. I am working on a c# application where I have about 15 methods that Update entries in the database. So I want to make one method for update with two parameters: Dictionary<int, object> dictionary and string tableName. The 'object' part of the dictionary will accept different ViewModels. Here is my code:

public void UpdateEntriesFromAGivenTable(Dictionary<int, object> dictionary, string tableName)
{
foreach (KeyValuePair<int, object> entry in dictionary)
{
Dictionary<string, object> dict = GetTypeNamesAndValuesWithReflection(entry.Value);

foreach (var item in dict)
{
if (item.Value != null && (!string.Equals(item.Key, "id")))
{
UpdateEntry(tableName, item.Key, item.Value, entry.Key);
}
}
}
}

But when I tried to use the above method, I receive the red underline below the parameter "Dictionary<int, user>" and the error message is: cannot convert from 'System.Collections.Generic.Dictionary<int, Models.User> to 'System.Collections.Generic.Dictionary<int, object>.

What I have tried:

I tried the following cast:

(Dictionary<int, object>)(users)

but without success. I looked for help in google and stackoverflow but did not find a similar issue. So can you tell me is it possible to cast a variable of Type: Dictionary<int, Models.User> to Dictionary<int, object> and if the answer is yes, how to do it? Thanks.

[Stephan van Hulst]

The problem is that both Dictionary and KeyValuePair are invariant. Dictionary<int, object> is not a supertype of Dictionary<int, user>. Normally you have to solve this by transforming the input before you pass it to the method:

dictionary.ToDictionary
<
  KeyValuePair<int, user>,
  int,
  object
>
(
  entry => entry.Key,
  entry => entry.Value
)

There's an easier way to solve your problem though. Make your method generic:

public void UpdateTable<TEntry>(IEnumerable<KeyValuePair<int, TEntry>> rows, string tableName)
{
  foreach ((int id, TEntry entry) in rows)
    foreach ((string columnName, object value) in GetTypeNamesAndValuesWithReflection(entry))
      if (columnName != "id" && value != null)
        UpdateEntry(tableName, columnName, value, id);
}

I also changed the code to use tuple type deconstruction, but for this to work with KeyValuePair you need C# 7 and .NET Core 2.