How to Map/Merge Two Objects in C# Using AutoMapper While Ignoring Default Values

Discover how to use AutoMapper to integrate two objects effectively in C# , avoiding default values for accurate data merging.
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How to Map/Merge Two Objects in C# Using AutoMapper While Ignoring Default Values

When working with web applications, especially those that interact with real-time data streams like websockets, keeping your objects in sync can pose various challenges. One specific issue arises when partial updates result in unwanted default values being assigned to your properties during the mapping process. This post explores a potential solution, specifically how to use AutoMapper to handle this delicate situation effectively.

The Problem: Merging Objects with Default Values

Imagine you have two instances of an object:

Initial Object: This contains all properties populated with values when received initially via a websocket.

Updated Object: This only provides information related to changes, meaning only certain properties will be updated, leaving others possibly re-assigned to their default values.

The default values may not reflect the intended state of your application. For example:

Strings - Map to null.

Floats - Default to 0.

Doubles - Default to 0.0d.

Booleans - Default to false.

Assigning these default values could lead to loss of important state information. A simple conditional check on each property you are mapping (using .ForMember) isn't practical when dealing with more than 50 properties.

AutoMapper Configuration Example

Your initial attempt at configuring AutoMapper would look something like this:

[[See Video to Reveal this Text or Code Snippet]]

While the code snippet utilizes a condition to avoid mapping when the source member is null, other types must also consider their default states, which complicates the process.

The Solution: Transitioning to JSON.NET

Instead of grappling with AutoMapper's configurations, the solution involves leveraging JSON.NET and its powerful JsonMergeSettings. Transitioning to JSON.NET allows you to control how properties are handled during the merge process more effectively.

Step-by-Step Approach

Create a Class with Default Value Handling:

Define your class and ensure to apply the JsonProperty attribute with the DefaultValueHandling.Ignore setting.

[[See Video to Reveal this Text or Code Snippet]]

Handle WebSocket Events:

In the event handler that processes incoming websocket data, use the following approach to manage the merging:

[[See Video to Reveal this Text or Code Snippet]]

Benefits of Using JSON.NET

Efficiency: Merging JSON before deserialization avoids additional overhead compared to comparing and updating the properties post-deserialization.

Flexibility: You can control how each property is handled without specifying conditions for each one manually.

Conclusion

Both AutoMapper and JSON.NET have their strengths, but in scenarios where default values hinder the mapping process, JSON.NET combined with JsonMergeSettings offers a more streamlined solution. Consider implementing this approach to maintain the integrity of your data without excessive boilerplate code, making your application more efficient and resilient.

With the knowledge shared here, you should be equipped to handle object mapping and updates in your C# applications effectively!