A class library for performing a diff of any 2 objects of the same type.
The easiest way to use ObjectDiffer is by loading the ObjectDifferModule ninject module:
var kernel = new StandardKernel(new ObjectDifferModule());
// you can now inject an IDiffer into your classes, or get an instance directly:
var differ = kernel.Get<IDiffer>();IDiffer has only one method, Diff<T>(T newObj, T oldObj). This returns a Difference object, or null if there is no difference. Difference has a property ChildDiffs which is a list of Difference objects representing the changes to child properties. It also contains the PropertyName ("self" for the top level object, and "Item" for items in an array), the NewValue and the OldValue.
-
The differ determines if 2 objects are equal using the
Equalsmethod, rather than reference equality. -
When the differ is diffing an array, it needs to determine which elements represent the same object in each list. For example:
class MyObj
{
public int Id { get; set; }
public string Name { get; set; }
}
public void DiffAList(){
var differ = kernel.Get<IDiffer>();
var obj1 = new MyObj{Id = 1, Name = "object"};
var obj2 = new MyObj{Id = 1337, Name = "another object"};
var oldList = new List<MyObj>{obj1, obj2};
var newList = new List<MyObj>{obj2, obj1}; //note that they are added in reverse order
var diff = differ.Diff(newList, oldList);
// we would expect the diff to be null, since the elements in the list are the same
// however, if the differ just compares the objects at each index of the array, it would think we have changed both elements
}To solve this problem, the differ assumes that if the hash code of the objects are equal, they are supposed to be the same object. So in the example above, we would just add a GetHashCode() method to MyObj:
class MyObj
{
public int Id { get; set; }
public string Name { get; set; }
public override int GetHashCode()
{
return Id;
}
}If you would like to employ a different strategy for determining equality, you can override the equality comparer that the differ uses like so:
// you have an IEqualityComparer called comparer that you would like to use
kernel.Rebind<IEqualityComparer<object>>().ToConstant(comparer).Named("SameObjectComparer");