How to Properly Override Equals() and GetHashCode() for LINQ's Except() Method?

Implementing Equals() and GetHashCode() Methods for Custom Classes: A Practical Example

Overriding the Equals() and GetHashCode() methods in custom classes is crucial for ensuring proper object comparison and hashing. This article demonstrates the correct way to implement these methods for your RecommendationDTO class to enable its use with LINQ's Except() method.

Implementing Equals()

To override Equals(), you need to provide a custom implementation that compares the objects based on their unique properties. In your case, the RecommendationId property is a suitable identifier. Here's the corrected implementation:

public override bool Equals(object obj)
{
    var item = obj as RecommendationDTO;

    if (item == null)
    {
        return false;
    }

    return this.RecommendationId.Equals(item.RecommendationId);
}

Implementing GetHashCode()

The GetHashCode() method generates a hash code for the object. For consistent comparison, the returned hash code should be the same for objects with the same identifying properties. In your case, you can return the hash code of the RecommendationId property:

public override int GetHashCode()
{
    return this.RecommendationId.GetHashCode();
}

Usage with LINQ Except()

With these overridden methods in place, you can now utilize the LINQ Except() method to exclude objects that are equal to each other based on their RecommendationId property. For example:

var list1 = new List<RecommendationDTO> { /* ... */ };
var list2 = new List<RecommendationDTO> { /* ... */ };

var result = list1.Except(list2);

Note: Make sure to check for null values and use the correct casing for properties and methods.

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