Table of Contents

Data Equality on Custom Data Models in 2sxc 17+

Custom data models such as AppCode.Data.Product or AppCode.Data.BlogPost are technically a wrapper around other objects usually coming from IEntitys.

As such, there is always the question how to check equality.

Tip

The key take away: use the == operator and use the .Equals() method and use .GroupBy() as you would expect.

We have done special modifications to the wrappers, so the == operator and item.Equals(item2) will work as expected.

Let's explain:

var item1 = As<Product>(MyItem);
var item2 = As<Product>(MyItem);

var isEqual = item1 == item2; // should this be true or false?

Technically the wrappers are different objects, as they were created independently. So in terms of what really happens, they are different, but for practical purposes they should behave as if they are the same. Here's why:

// Get a list of all blog posts, then group by category
var blogPosts = AsList<BlogPost>(MyItems);
var grouped = blogPosts.GroupBy(p => p.Category);

Internally every item was wrapped as a BlogPost. Each one will also get the Category which was also wrapped independently. But for grouping by something, the should be considered equal.

Equality Implementation

  1. we have overloaded the == and != operators to compare the underlying IEntity objects.
  2. we have implemented the .Equals() method to compare the underlying IEntity objects.

This means that you can use the == operator and the .Equals() method as you would expect. It also means that LINQ operations such as GroupBy will work as expected.

Difference to ITypedItem

Important

This is a different than the implementation on ITypedItem. There we could only override .Equals(), so that and GroupBy would work as expected, but the == operator would not work as expected in ITypedItem.

Edge Cases

If rare cases where you extend the Data Model eg. BlogPost with additional properties, such as this

namespace AppCode.Data
{
  public partial class BlogPost
  {
    public string CustomProperty { get; set; }
  }
}

...you may have two different objects, because you set that property on one and not the other. In this case, you may still want to check for equality and expect it to be false, but the underlying check would compare the inner data and return true.

We believe this is a very, very rare scenario. If you want to do this, and expect two wrappers around the same data to be un-equal, you'll need to use ReferenceEquals.

History

  • .Equals implemented in v17.03
  • == and != operators implemented in v17.04
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