Question

I have a Customer class.

public class Customer {     private string _id;     private string _name;     // some more properties follow  

I am inheriting the EqualityComparer form MyEqualityComparer(of Customer).
This I am intending to use in LINQ queries.
MyEqualityComparer is intended for partial check between two objects.
If the customer.id and customer.name matches I treat the objects the equal.

public class MyComparer : System.Collections.Generic.EqualityComparer<Customer> {     public override bool Equals(Customer x, Customer y)     {         if (x.Id == y.Id && x.Name == y.Name)             return true;         else             return false;     }      public override int GetHashCode(Customer obj)     {         return string.Concat(obj.Id,obj.Name).GetHashCode();     }  } 

I referred to generating hashcode.
I am little unsure about concatenating strings and using that as a hashcode.
Is this safe and sound what I am trying to do ?

Answer 1

See this question on hashcodes for a pretty simple way to return one hashcode based on multiple fields.

Having said that, I wouldn’t derive from EqualityComparer<T> myself – I’d just implement IEqualityComparer<T> directly. I’m not sure what value EqualityComparer<T> is really giving you here, other than also implementing the non-generic IEqualityComparer.

A couple more things:

• You should handle nullity in Equals

• Your present Equals code can be simplified to:

  return x.Id == y.Id && x.Name == y.Name; 

A fuller implementation of Equals might be:

public override bool Equals(Customer x, Customer y) {     if (object.ReferenceEquals(x, y))     {         return true;     }     if (x == null || y == null)     {         return false;     }     return x.Id == y.Id && x.Name == y.Name; }