Help with static constructor in c#

Question

I need help initializing static readonly variables in c#. I have a class with this signature

public class AgentDescriptions
{
   public static readonly int P1;
   public static readonly int P2;

   static AgentDescriptions()
   {
      int agencyID = 1; //I need to pass this in the constructor somehow
      P1 = GetIDFromDB(agencyID);
      P2 = GetIdFromDB(agencyID);
   }
}

P1 and P2 are used over and over in the application and I am trying to avoid two things. 1)Magic numbers and 2)trip to the DB every time I need to use P1 and P2.

In the application I am using them in many places in this manner

if (something == AgentDescriptions.P1)
   //Blah();

Please help. How can I pass the agencyID in the static constructor? If I add another contructor and pass agencyID there, will I have to initialize the class every time I use it? will this mean a trip to the DB every time?

You can't pass a static constructor parameters. See MSDN: msdn.microsoft.com/en-us/library/k9x6w0hc(v=VS.90).aspx — Jim Schubert
– Jim Schubert, Commented Oct 7, 2010 at 17:10
Massive code smell as well, I really doubt you need to do this, I haven't ever had such a need — meandmycode
– meandmycode, Commented Oct 7, 2010 at 17:12
You can pass argument to public static void Main() when you are calling your project. Inside Main method initialize P1 & P2. — sh_kamalh
– sh_kamalh, Commented Oct 7, 2010 at 17:35

Kendrick · Accepted Answer · 2010-10-07 17:08:26Z

5

Why is the class static. If you're passing a variable in to the constructor you're implying an instance of an object with state, not a class.

I'd make the variables private member variables with only get methods available for them. Then you have a constructor that takes the agency ID and sets those two variables. If you need to maintain a single instance of this type, then use a singleton (static function in the class that stores a single instance of the object or creates a new object if one doesn't exist yet). On the other hand, if you need multiple objects with different agency IDs, you've already got a mechanism to do that.

answered Oct 7, 2010 at 17:08

Kendrick

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5 Comments

Powerlord Over a year ago

+1 for suggesting a singleton. Also, I apologize for ruining your perfect 1,000 rep. :/

George Stocker Over a year ago

Ug, singletons. still +1. Just don't like Singletons.

Kendrick Over a year ago

@George Stocker I was going to mention that Singletons were controversial, but I figure they're still better than the original form. They'll plug in fairly smoothly with the current design while allowing easier replacement with an alternative later on.

Rune FS Over a year ago

Almost hit the -1 there, singlton is not the solution especially in the presence of a strong smell of nor understanding state

Kendrick Over a year ago

This may actually be a case for a singleton, since he's following the rules I'd follow if I were going to use one (state remains the same through the lifecycle of the object, and when you instantiate the first instance has no bearing on the state) That said, given the agencyID being passed in, I think there may be some other issues...

CodingGorilla · Accepted Answer · 2010-10-07 17:09:27Z

2

I would do it like this:

public static class AgentDescriptions
{
  public static int P1 { get; private set; }
  public static int P2 { get; private set; }

  public static void Initialize(int AgencyId)
  {
      P1 = GetIDFromDB(AgencyId);
      P2 = GetIDFromDB(AgencyId);
  }
}

If you want to lock it so Initialize can only be called once, then you can easily just use a flag that throws an exception (or whatever) after Initialize has been called.

answered Oct 7, 2010 at 17:09

CodingGorilla

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Comments

Austin Salonen · Accepted Answer · 2010-10-07 17:10:43Z

2

It really sounds like you want a cache of sorts.

public class AgentDescriptions
{
    static Dictionary<int,int> agentCache = new ...;
    public static int GetP1(int agentID)
    {
       if (!agentCache.ContainsKey(agentID))
          agentCache.Add(agentID, GetIdFromDB(agencyID));

       return agentCache[agentID];
    }

    ...

answered Oct 7, 2010 at 17:10

Austin Salonen

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Comments

Community · Accepted Answer · 2017-05-23 12:11:47Z

1

There was similar singleton issue in some other question here.

class AgentDescriptions 
{
    AgentDescriptions()
    {
        P1 = GetIDFromDB(agencyID);
        P2 = GetIdFromDB(agencyID);
    }
    static public AgentDescriptions Instance 
    {
        get 
        {
            if (_instance==null)
            {
                _instance=new AgentDescriptions();
            }
            return _instance;
        }
    }
    static private _instance;
}

and get your results with

int x=AgentDescriptions.Instance.P1;

Look into:

How to restrict user for checking null for singelton instance in C#, .NET?

I use that pattern often for configuration or constant items.

edited May 23, 2017 at 12:11

CommunityBot

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answered Oct 7, 2010 at 17:11

Daniel Mošmondor

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Comments

RLH · Accepted Answer · 2010-10-07 17:29:27Z

1

would try something like this...

int p1 = -1; //Or some impossible value.  This could also be a int? and left as null until it is initialized.
public static int P1
{
    get //Define only the 'get' of the property for this to make it readonly
    {
        if (p1 == -1)
           //Insert Code to get & assign the value of p1 from your DB.
        return p1;
    }
}

edited Oct 7, 2010 at 17:29

answered Oct 7, 2010 at 17:05

RLH

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Comments

Charles Bretana · Accepted Answer · 2010-10-08 13:53:13Z

1

You don't need an initializer (static constructor). if agencyId is an integer, try This

public static class AgentDescriptions  
{ 
   private static readonly Dictionary<int, int> dic
        = new Dictionary<int, int>();
   public static int GetId(int agencyId)
   {
       if (!dic.ContainsKey(agencyId))
            Adic.dd(agencyId, GetIDFromDB(agencyID));
       return dic[agencyId];
   }
 // ...

and use it like this:

   if (something == AgentDescriptions.GetId(agencyId)) 
   //Blah();

or, if agencyId is a string, or you want to use strings like "P1", "P2" etc as keys, then

public static class AgentDescriptions 
{ 
   private static readonly Dictionary<string, int> dic
        = new Dictionary<string, int>();

   public static int GetId(string agencyId)
   {
       if (!dic.ContainsKey(agencyId))
           Adic.dd(agencyId, GetIDFromDB(agencyID));
       return dic[agencyId];
   }
 // ...

and use it like this:

   if (something == AgentDescriptions.GetId("P1") 
   //Blah();

if the list of Agencies is fixed, you can add preconfigured static members to retrieve the Id for those agencies...

public static class AgentDescriptions
{
    private static readonly Dictionary<string, int> dic
        = new Dictionary<string, int>();
    public static int P1 { get { return GetId("P1"); } }
    public static int P2 { get { return GetId("P2"); } }
    public static int P3 { get { return GetId("P3"); } }
    public static int GetId(string agencyId)
    {
        if (!dic.ContainsKey(agencyId))
            dic.Add(agencyId, 12);
        return dic[agencyId];
    }

and use it like this:

   if (something == AgentDescriptions.P1) 
   //Blah();

edited Oct 8, 2010 at 13:53

answered Oct 7, 2010 at 17:05

Charles Bretana

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4 Comments

Nick Masao Over a year ago

Where do I define or set agencyID?

Charles Bretana Over a year ago

If this is static, I assume it's always the same (If it can change then you better not be putting it in static class). So if it is immutable, either hard code it or put it in config file and fetch it in another static initializor field (as shown above)

Charles Bretana Over a year ago

if it can change then this class should not be static... You need to completely redesign this to be an instance class with state, so you can have one for each Agency... Or, make a static Dictionary<int, AgentDescriptions> class that has one member for each AgencyId, which is initialized on startup for every Agency, or initialized for each agency the first time that agency is referened...

Nick Masao Over a year ago

Thanks Charles I'll go with your approach. I just need to initialize once on startup for each agency.

patrick · Accepted Answer · 2010-10-08 14:21:49Z

1

Using a UID like AgencyID implies that you are going to have multiple instances of an object. Static means you only get one object. Remove the static keywords and make instances of your object.

answered Oct 8, 2010 at 14:21

patrick

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Comments

Andriy Buday · Accepted Answer · 2010-10-07 17:54:30Z

0

Since you are trying to pass some values inside of static fields/properties, and then access them, we may think about static class properties as about SINGLETON, since once they are initialized you never change them (or at least you don't want to do that), so that is what I would suggest.

answered Oct 7, 2010 at 17:54

Andriy Buday

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1 Comment

Rune FS Over a year ago

And most often they are both a smell not a solution

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