Flags with web services

Question

I have a flag attribute enumeration that is behind a web service as follows:

[Serializable,Flags]
public enum AccessLevels
{
    None = 0,
    Read = 1,
             


        

Answer 1

I had a similar problem and got round it by adding another web service to return the currect flag values first.

Those then became the values I used in the compare.

Might not be the cleanest solution but it works.

Edit:

My original answer suggested that the values are passed across as a separate web service rather than within an enum.

However, poking around, it appears that an enumeration of 0,1,2 being mapped to 1,2,4 across a web service (even that the [Flags] attribute is set) is a common problem.

The solution suggested by a number of people is to modify the original enumeration definition and start from 1 rather than 0.

Answer 2

One option would be to provide a more verbose class instead of the enum e.g.

[Serializable]
public class AccessPermission{
 public boolean None{get;set;}
 public boolean Read{get;set;}
 public boolean Write{get;set;}
 public boolean Full{get;set;}

 public AccessPermission(AccessLevels level){
  None = false;
  Read = false;
  Write = false;
  Full = false;

  switch(level){
  case AccessLevels.None:
   break;
  case AccessLevels.Read:
   Read = true;
   break;
  case AccessLevels.Write:
   Write = true;
   break;
  case AccessLevels.Full:
   Read = true;
   Write = true;
   Full = true;
   break;
  }
 }
} 

The other option I can see is providing a method in what ever language they are using to successfully interoperate the integer you are sending. The flag operator means that c# does bit masking to find if a individual flag is marked

0001 -> None
0010 -> Read
0100 -> Write
0110 -> Full

so to check for any permission you should see if that bit is set

public static boolean CanRead(int accessLevel){
 return (accessLevel | 2) > 0 // return true if read bit set, using bitwise or
}

public static boolean CanWrite(int accessLevel){
 return (accessLevel | 4) > 0 // return true of write bit set.
}

Please note this second solution is more fragile, if you change the definition of accessLevels you client will silently miss behave.

Answer 3

I have done extensive research on this and found that it is not possible to serialize enumeration constants through a web service. Note that to accomplish your goal you don't need the enumerations None or Full. These two enumerations can be implied with read / write combination:

You could assume full access if your AccessLevels = Read | Write and none if your AccessLevels = 0 [nothing]

Your enumerations would look like this:

[Serializable,Flags]
public enum AccessLevels
{
    Read = 1,
    Write = 2
}

Answer 4

Flags should be multiples of two, and in your case your flags are (0,1,2,3). Try change your definition of the struct to:

[Serializable,Flags]
public enum AccessLevels{    
None = 1,    
Read = 2,    
Write = 4,    
Full = Read | Write}

And see if it works better.

(I hope Im not making a fool of myself, its late and Im on my way to the bed.. )