ICollection<string> ValueComparer results in "Argument types do not match" - entity-framework

Question

Following the Collection of Primitives sample code, I've made my own variation:
public class AttachmentTagsConfiguration : IEntityTypeConfiguration<Attachment>
{
public void Configure(EntityTypeBuilder<Attachment> builder)
{
builder.Property(e => e.Tags).HasConversion(
v => string.Join( ' ', v.Select(x => x.ToLower()).Distinct() ),
v => v.Split( ' ', StringSplitOptions.RemoveEmptyEntries )
.Select( x => x.ToLower() )
.Distinct()
.ToList(),
new ValueComparer<ICollection<string>>(
(c1, c2) => c1.SequenceEqual(c2),
c => c.Aggregate(0, (a, v) => HashCode.Combine(a, v.GetHashCode())),
c => c.ToList()
)
);
}
}
Tags have no spaces, so we just join them together in the database to create a single string. This is what the schema looks like:
public class Attachment
{
...
public ICollection<string> Tags { get; set; }
}
If I leave the ValueComparer in there, I get the following error when loading a query that has an Attachment:
System.ArgumentException: 'Argument types do not match'
However, if I remove the ValueComparer it works fine. But then I assume change tracking won't work correctly?
I'm not sure what part of the comparer code could lead to an incorrect argument type. None of the records in the database have a NULL value for Tags, so I don't see how there could be any null values.
Attachments is an ancestor class - we have AssetAttachments, InspectionAttachments, UnitAttachments and DefectAttachments. Does this have an impact on the SequenceEqual comparison?

Answer 1

Oh I see! I removed the casts that were in the original code:
public void Configure(EntityTypeBuilder<Attachment> builder)
{
builder.Property( e => e.Tags ).HasConversion(
v => string.Join( ' ', v.Select( x => x.ToLower()).Distinct() ),
v => (ICollection<string>)v.Split( ' ', StringSplitOptions.RemoveEmptyEntries )
.Select( x => x.ToLower() )
.Distinct()
.ToList(),
new ValueComparer<ICollection<string>>(
(c1, c2) => c1.SequenceEqual(c2),
c => c.Aggregate(0, (a, v) => HashCode.Combine(a, v.GetHashCode())),
c => (ICollection<string>)c.ToList()
)
);
}
Visual Studio was showing me this:
The cast is dimmed on the line highlighted! So I removed it when I shouldn't have!