Entity Framework Core Interview Question #153

What is a ValueComparer in EF Core?

Advanced Mapping, Interceptors, Value Conversions & Architecture Senior Advanced

Quick Interview Answer

A ValueComparer tells EF Core how to compare, snapshot, and hash property values when ordinary CLR equality is insufficient. It is especially relevant for mutable collections or custom value types used with value conversion. Without an appropriate comparer, EF Core may fail to detect in-place changes correctly.

Detailed Explanation

A ValueComparer tells EF Core how to compare, snapshot, and hash property values when ordinary CLR equality is insufficient. It is especially relevant for mutable collections or custom value types used with value conversion. Without an appropriate comparer, EF Core may fail to detect in-place changes correctly.

Code Example

var comparer = new ValueComparer<List<string>>(
    (a,b) => a!.SequenceEqual(b!),
    v => v.Aggregate(0,(x,y)=>HashCode.Combine(x,y.GetHashCode())),
    v => v.ToList());