Creating a unique hash code based on some properties of an object [duplicate]

Question

I have to following classes:

public class NominalValue
{
   public int Id {get; set;}
   public string ElementName {get; set;}
   public decimal From {get; set;}  
   public decimal To {get; set;}    
   public bool Enable {get; set;}   
   public DateTime CreationDate {get; set;}
   public int StandardValueId {get; set;}  //FK for StandardValue
} 
public class StandardValue
{
   public int Id {get; set;}
   public string ElementName {get; set;}
   public decimal From {get; set;}  
   public decimal To {get; set;}    
   public bool Enable {get; set;}   
   public DateTime CreationDate {get; set;}
}

User wants to fill nominalValue object properties. filling the nominalValue properties can performed in 2 way:

User fill values for nominalValue manually.
User Load values for nominalValue from a standardValue object and then change some values or not.

sometimes I need to know if some property of nominalValue objects for a specified Element are equal to corresponding standardValue or not?

I don't want to load standardValue from Db for checking this equality, so I decided to define a HashValue property in NominalValue class:

public class NominalValue
{
   public int Id {get; set;}
   public string ElementName {get; set;}
   public decimal From {get; set;}  //<-- 1st parameter for generating hash value
   public decimal To {get; set;}    //<-- 2nd parameter for generating hash value
   public bool Enable {get; set;}   //<-- 3rd parameter for generating hash value 
   public DateTime CreationDate {get; set;}
   public int StandardValueId {get; set;}  
   public string HashValue {get;set;}      //<-- this property added
}

when user fill nominalValue properties using standardValue properties, I calculate its value based on 3 properties(From, To, Enable) and save it with other properties, and when I check if that nominalValue fill with standardValue or not, I calculate hash code for From, To, Enable and compare the result with HashValue (instead loading standardValue from Db).

Is there any mechanism to calculate a unique hash code based on 3 property values(From, To, Enable)?

This is a good starting point stackoverflow.com/questions/371328/… — Alexander Schmidt
– Alexander Schmidt, Commented Jan 5, 2016 at 8:13

Quentin Roger · Accepted Answer · 2016-01-05 08:44:46Z

5

You can try to do something like this :

private int GetHashValue() {
    unchecked 
    {
        int hash = 17;
        //dont forget nullity checks 
        hash = hash * 23 + From.GetHashCode();
        hash = hash * 23 + To.GetHashCode();
        hash = hash * 23 + Enable.GetHashCode();
        return hash;
    }
}

You can use the GetHashCode method on an anonymous type too

private int GetHashValue() {
   return new { From, To, Enable }.GetHashCode();
}

edited Jan 5, 2016 at 8:44

answered Jan 5, 2016 at 8:17

Quentin Roger

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3 Comments

xr280xr Over a year ago

Magic numbers should always be commented, but especially in a SO answer.

Quentin Roger Over a year ago

The idea is to take two different prime numbers, it comes from this book amazon.com/dp/0321356683

André Boonzaaijer Over a year ago

The GetHashCode from an anonymous object is way more elegant and portable and should be the (separate) accepted answer in my opinion.

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