My dapper class mapper I have defined doesn’t appear to be used

I have a class this is defined in a DLL class that I’m trying to keep pure.

public sealed class JointCost : Changeable, ICloneable
{
    [Key]
    public Guid JointCostId { get; init; } = Guid.NewGuid();
    public string JointTypeName { get; set; }
    public decimal JointPrice { get;set; }
    public JointCostType CostType { get; set; }
    public JointType JointType { get; set; }
}

[Flags]
public enum JointType
{
    Glue = 1 << 0,
    Tape = 1 << 1,
    Stitch = 1 << 2,
    Other = 1 << 3,
}

public enum JointCostType
{
    Per1000LinearFeet,
    Per1000SquareInch
}

public enum EChangeable
{
    None,
    New,
    Updated,
    Removed
}

public abstract class Changeable
{
    private EChangeable _changes = EChangeable.None;
    public EChangeable Changes { get => _changes;
        set
        {
            if(value == EChangeable.Removed) {_changes = value; }
            else if(value == EChangeable.New) {_changes = value; }
            else if(value == EChangeable.Updated) {_changes = value; }
        }
    }
}

in my webapp project I have a DAL class using dapper where I make a generic database call like so

public async Task<IEnumerable<int>> InsertItemsAsync<T>(IEnumerable<T> items) 
    where T : Changeable            
{
    var returnedIds = new List<int>();
    using (var connection = new SqlConnection($"{_connectionString} Database={tenantId};"))
    {
        foreach (var item in items)
        {
            returnedIds.Add(await connection.InsertAsync(items));
        }
    }
    items.All(x => { x.Changes = EChangeable.None; return false; });
    return returnedIds;
}

I wrote a unit test (which is another project) that calls this method like so

[Test]
public async Task GetVendorObject()
{
var newJointCost = new JointCost();
var ids = await _dataContext.InsertItemsAsync(new[] { newJointCost });
}

I get a runtime error “Microsoft.Data.SqlClient.SqlException : Invalid column name ‘Changes’.” So I tried to make a mapping class

so i hadded a mapper class to the webapp project

public class JointCostMapper : ClassMapper<JointCost>
{
    public JointCostMapper()
    {
        Table("JointCosts");
        Map(m => m.Changes).Ignore();
        AutoMap();
    }
}

and in my test method added default mapper and mapping assemblies like so

[Test]
public async Task GetVendorObject()
{
    DapperExtensions.DapperExtensions.SetMappingAssemblies(new[] { typeof(JointCostMapper).Assembly });
    DapperExtensions.DapperExtensions.DefaultMapper = typeof(JointCostMapper);
    DapperExtensions.DapperAsyncExtensions.SetMappingAssemblies(new[] { typeof(JointCostMapper).Assembly });
    DapperExtensions.DapperAsyncExtensions.DefaultMapper = typeof(JointCostMapper);
    var newJointCost = new JointCost();
    var ids = await _dataContext.InsertItemsAsync(new[] { newJointCost });
}

However, after these changes I still get the error that the column ‘Changes’ is invalid. Which is correct as there is not a column ‘changes’, though with the mapper, it should be ignoring the changes property when trying to write.

what am I doing wrong.

I also don’t think I should be setting a default mapper as I’m going to map multiple complex composite objects.