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    <p><code>IComparable</code> is for ordering comparisons. Either use <code>IEquatable</code> instead, or just use the static <code>System.Object.Equals</code> method. The latter has the benefit of also working if the object is not a primitive type but still defines its own equality comparison by overriding <code>Equals</code>.</p> <pre><code>object originalValue = property.GetValue(originalObject, null); object newValue = property.GetValue(changedObject, null); if (!object.Equals(originalValue, newValue)) { string originalText = (originalValue != null) ? originalValue.ToString() : "[NULL]"; string newText = (newText != null) ? newValue.ToString() : "[NULL]"; // etc. } </code></pre> <p>This obviously isn't perfect, but if you're only doing it with classes that you control, then you can make sure it always works for your particular needs.</p> <p>There are other methods to compare objects (such as checksums, serialization, etc.) but this is probably the most reliable if the classes don't consistently implement <code>IPropertyChanged</code> and you want to actually know the differences.</p> <hr> <p>Update for new example code:</p> <pre><code>Address address1 = new Address(); address1.StateProvince = new StateProvince(); Address address2 = new Address(); address2.StateProvince = new StateProvince(); IList list = Utility.GenerateAuditLogMessages(address1, address2); </code></pre> <p>The reason that using <code>object.Equals</code> in your audit method results in a "hit" is because the instances are actually not equal!</p> <p>Sure, the <code>StateProvince</code> may be empty in both cases, but <code>address1</code> and <code>address2</code> still have non-null values for the <code>StateProvince</code> property and each instance is different. Therefore, <code>address1</code> and <code>address2</code> have different properties.</p> <p>Let's flip this around, take this code as an example:</p> <pre><code>Address address1 = new Address("35 Elm St"); address1.StateProvince = new StateProvince("TX"); Address address2 = new Address("35 Elm St"); address2.StateProvince = new StateProvince("AZ"); </code></pre> <p>Should these be considered equal? Well, they will be, using your method, because <code>StateProvince</code> does not implement <code>IComparable</code>. That's the only reason why your method reported that the two objects were the same in the original case. Since the <code>StateProvince</code> class does not implement <code>IComparable</code>, the tracker just skips that property entirely. But these two addresses are clearly not equal!</p> <p>This is why I originally suggested using <code>object.Equals</code>, because then you can override it in the <code>StateProvince</code> method to get better results:</p> <pre><code>public class StateProvince { public string Code { get; set; } public override bool Equals(object obj) { if (obj == null) return false; StateProvince sp = obj as StateProvince; if (object.ReferenceEquals(sp, null)) return false; return (sp.Code == Code); } public bool Equals(StateProvince sp) { if (object.ReferenceEquals(sp, null)) return false; return (sp.Code == Code); } public override int GetHashCode() { return Code.GetHashCode(); } public override string ToString() { return string.Format("Code: [{0}]", Code); } } </code></pre> <p>Once you've done this, the <code>object.Equals</code> code will work perfectly. Instead of naïvely checking whether or not <code>address1</code> and <code>address2</code> literally have the same <code>StateProvince</code> reference, it will actually check for semantic equality.</p> <hr> <p>The other way around this is to extend the tracking code to actually descend into sub-objects. In other words, for each property, check the <code>Type.IsClass</code> and optionally the <code>Type.IsInterface</code> property, and if <code>true</code>, then recursively invoke the change-tracking method on the property itself, prefixing any audit results returned recursively with the property name. So you'd end up with a change for <code>StateProvinceCode</code>.</p> <p>I use the above approach sometimes too, but it's easier to just override <code>Equals</code> on the objects for which you want to compare semantic equality (i.e. audit) and provide an appropriate <code>ToString</code> override that makes it clear what changed. It doesn't scale for deep nesting but I think it's unusual to want to audit that way.</p> <p>The last trick is to define your own interface, say <code>IAuditable&lt;T&gt;</code>, which takes a second instance of the same type as a parameter and actually returns a list (or enumerable) of all of the differences. It's similar to our overridden <code>object.Equals</code> method above but gives back more information. This is useful for when the object graph is really complicated and you know you can't rely on Reflection or <code>Equals</code>. You can combine this with the above approach; really all you have to do is substitute <code>IComparable</code> for your <code>IAuditable</code> and invoke the <code>Audit</code> method if it implements that interface.</p>
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    1. COUnfortunately using just object.Equals is returning true for reference types, for example: [Address] StateProvince changed from 'MyAccountService.StateProvince' to 'MyAccountService.StateProvince'
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    2. CO@Pete Nelson: Assuming you're actually comparing different references, that's... improbable. Can we see a complete example with the class? Does it override the `Equals` method? I use code very similar to this and it never gives false negatives.
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