DeleteRequestHandlerFK.cs, handling foreign key exception messages individually for different tables

DeleteRequestHandlerFK.cs

// *** All credits for the base idea to JajQ / Volkan Ceylan ***

using Serenity.Data;
using System;
using System.Data.SqlClient;
using <your solution name>;  // Enter the namespace of your solution here

namespace Serenity.Services
{
    public class DeleteRequestHandlerFK<TRow> : DeleteRequestHandler<TRow>
        where TRow: Row, IIdRow, new()
    {
        protected override void ExecuteDelete()
        {
            try
            {
                base.ExecuteDelete();
            }
            catch (Exception e)
            {
                string OutputMessage = string.Empty;

                ForeignKeyExceptionInfo fk;
                if (SqlExceptionHelper.IsForeignKeyException(e, out fk))

                    switch ((Row.Table.ToLower() + "--" + fk.TableName.ToLower()))
                    {
                        case "[dbo].[supplier]--delivery":  // *** Replace "[dbo].[supplier]" with the table associated with the entity where the exception is thrown and replace "delivery" with the foreign table ***
                          OutputMessage = "Sorry, but you cannot delete a supplier when this supplier is still used within a delivery. No delete has occured";    // *** Replace with your individual error mesage ***
                          break;
                            
                        default:
                          OutputMessage = String.Format("Sorry, but you cannot delete this. Table '{0}' has related records!", fk.TableName);
                          break;
                    }

                throw new ValidationError(OutputMessage);

                throw;
            }
        }
    }
}

then, within your xyzRepository.cs files, replace the line:
private class MyDeleteHandler : DeleteRequestHandler { }

with

private class MyDeleteHandler : DeleteRequestHandlerFK { }