How to override GetHashCode when a Date matches if plus or minus seven days

Question

If I have the following methods:

public bool Equals(VehicleClaim x, VehicleClaim y)
{           
    bool isDateMatching = this.IsDateRangeMatching(x.ClaimDate, y.ClaimDate);
    // other properties use exact matching
}

private bool IsDateRangeMatching(DateTime x, DateTime y)
{       
    return x >= y.AddDays(-7) && x <= y.AddDays(7);           
}

I am comfortable overriding GetHashcode when the values exactly match but I really have no idea how to do it when a match is within a range like this.

Can anyone help please?

Answer 1

I agree with Chris that

But if you have Date1 as Oct1, Date2 as Oct6, Date3 as Oct12. Date1 == Date2, and Date2 == Date3, but Date1 != Date3 is a strange behavior and the Equals purpose is not what you should use.

I don't really know if you are developping something new and if you have a database containing your vehicule claims, but I would have associated claims in the database as parent child relationship. What you have to ask yourself is: Is it possible that 2 vehicule claims within your date range can be different? Is there any other property you can use to identify a claim as unique?

Maybe you could resolve your problem this way:

Having a

List<VehicleClaim> RelatedClaims 

property in your VehicleClaim object.

Instead of Equals, use a function

bool IsRelated(VehicleClaim vehiculeClaim)
{ 
  if(all properties except date are equals)
  {  
     // since claims are sorted by date, we could compare only with the last element
     foreach(var c in RelatedClaims){ 
        if (IsDateRangeMatching(this.ClaimDate, c.ClaimDate)) 
           return true;
     }
  }

  return false;
}

and add code to construct your object

List<VehiculeClaim> yourListWithDuplicatesSortedByDate;
List<VehiculeClaim> noDuplicateList = new List<VehiculeClaim>();
foreach(var cwd in yourListWithDuplicatesSortedByDate)
{
  var relatedFound = noDuplicateList.FirstOrDefault(e => e.IsRelated(cwd));

  if (relatedFound != null)
    relatedFound.RelatedClaims.Add(cwd);
  else
    noDuplicateList.Add(cwd);
}

Problem with this, your claims must be sorted by date and it could not be the most efficient way to accomplish that.