adding SetValueComparer to modelBuilder - asp.net-mvc

Question

just wondering how I can get rid of this warning:
Microsoft.EntityFrameworkCore.Model.Validation[10620]
The property 'FI' on entity type 'Routes' is a collection or enumeration type with a value converter but with no
value comparer. Set a value comparer to ensure the
collection/enumeration elements are compared correctly.
Code:
modelBuilder.Entity<Routes>().Property(l => l.FI).HasConversion(
FI=> String.Join(",", FI),
dbVal => dbVal.Split(',', StringSplitOptions.RemoveEmptyEntries).ToList()
);
where FI is defined in the model as:
public List<string> FI { get; set; }
I understand I have to do a SetValueComparer call somehow but I am not sure how. The examples on line are a bit different and don't have the String.Join and dbVal lines.
Thank you

Answer 1

From the Microsoft docs - this is a example of how to set a value comparer (inside of HasConversion()):
modelBuilder
.Entity<EntityType>()
.Property(e => e.MyListProperty)
.HasConversion(
v => JsonSerializer.Serialize(v, (JsonSerializerOptions)null),
v => JsonSerializer.Deserialize<List<int>>(v, (JsonSerializerOptions)null),
new ValueComparer<List<int>>(
(c1, c2) => c1.SequenceEqual(c2),
c => c.Aggregate(0, (a, v) => HashCode.Combine(a, v.GetHashCode())),
c => c.ToList()
)
);
You need to choose the appropriate value comparison, of course (List<string> instead of List<int>, for example).
UPDATE: adapted to your code snippet, it should look like this (don't know, if it works, though):
modelBuilder
.Entity<Routes>()
.Property(l => l.FI)
.HasConversion(
fi => String.Join(",", fi),
dbVal => dbVal.Split(',', StringSplitOptions.RemoveEmptyEntries).ToList(),
new ValueComparer<List<string>>(
(c1, c2) => c1.SequenceEqual(c2),
c => c.Aggregate(0, (a, v) => HashCode.Combine(a, v.GetHashCode())),
c => c.ToList()
)
);