Why am I getting duplicated row inserts? - linq

Question

I have windows phone 7 application and classes for database mapping.
A Poll class looks like that:
[Table]
public class Poll // :BaseModel
{
//private int _pid;
//private string _pdesc;
//private bool _pisopen;
//private string _pname;
//private bool _prandom;
//private string _qlastupdticks;
//private string _ticks;
[Column(DbType = "INT NOT NULL IDENTITY(1,1)", IsPrimaryKey = true, IsDbGenerated = true)]
public int id { get; set; }
[Column(DbType = "INT")]
public int pid { get; set; }
//{
// get { return _pid; }
// set { SetValue(ref _pid, value, GetPropertyName(MethodBase.GetCurrentMethod())); }
//}
[Column]
public string pdesc { get; set; }
//{
// get { return _pdesc; }
// set { SetValue(ref _pdesc, value, GetPropertyName(MethodBase.GetCurrentMethod())); }
//}
[Column]
public bool pisopen { get; set; }
//{
// get { return _pisopen; }
// set { SetValue(ref _pisopen, value, GetPropertyName(MethodBase.GetCurrentMethod())); }
//}
[Column]
public string pname { get; set; }
//{
// get { return _pname; }
// set { SetValue(ref _pname, value, GetPropertyName(MethodBase.GetCurrentMethod())); }
//}
[Column]
public bool prandom { get; set; }
//{
// get { return _prandom; }
// set { SetValue(ref _prandom, value, GetPropertyName(MethodBase.GetCurrentMethod())); }
//}
[Column(DbType = "NVARCHAR(255)")]
public string qlastupdticks { get; set; }
//{
// get { return _qlastupdticks; }
// set { SetValue(ref _qlastupdticks, value, GetPropertyName(MethodBase.GetCurrentMethod())); }
//}
[Column(DbType = "NVARCHAR(255)")]
public string ticks { get; set; }
//{
// get { return _ticks; }
// set { SetValue(ref _ticks, value, GetPropertyName(MethodBase.GetCurrentMethod())); }
//}
public override bool Equals(object obj)
{
var item = obj as Poll;
if (item != null)
{
Equals(item);
}
return false;
}
public bool Equals(Poll other)
{
if (ReferenceEquals(null, other)) return false;
return (other.pid == pid);
}
public override string ToString()
{
return string.Format("{0}_{1}", GetType().Name, pid);
}
public override int GetHashCode()
{
return ToString().ToUpper().GetHashCode();
}
}
Save method looks like that:
public bool RowsSave<T>(IEnumerable<T> entities, out string error)
{
error = string.Empty;
bool res;
var type = typeof (T);
using (var ctx = new PpaDataContext(_connectionString))
{
try
{
var entitesInDb = ctx.GetTable(type).Cast<T>().ToList();
var entitesForSave = new List<T>();
foreach (var entity in entities)
{
if (!entitesInDb.Contains(entity))
{
entitesForSave.Add(entity);
}
else
{
var index = entitesInDb.IndexOf(entity);
foreach (var prop in PropertiesGet(entity))
{
prop.SetValue(entitesInDb[index], prop.GetValue(entity, null), null);
}
}
}
if(entitesForSave.Count > 0)
{
ctx.GetTable(type).InsertAllOnSubmit(entitesForSave);
}
ctx.SubmitChanges();
res = true;
}
catch (Exception ex)
{
error = string.Format("{0}", ex.Message);
res = false;
}
}
return res;
}
When I try insert, each object inserts twice. What incorrect in this code?
The RowsSave method calling one time only.

Answer 1

This is a bit after the fact, but I've run into the exact same problem. This has to do with an error in overridden equality operators. In this specific case, the problem appears because the code does not return the value of the Equals function in:
public override bool Equals(object obj)
{
var item = obj as Poll;
if (item != null)
{
Equals(item);
}
return false;
}
That code will always return false. The corrected code should be:
public override bool Equals(object obj)
{
var item = obj as Poll;
if (item != null)
{
return Equals(item);
}
return false;
}
LINQ-to-SQL uses the object equals comparison after insertions. I'm not sure in what context and for what reason this happens, but if the comparison returns false, it runs the insertion again. If you're experiencing the same behavior, check any overridden equality methods for your entity for correctness.

Answer 2

I don't think you need the line:
ctx.SubmitChanges();
as an insert is being done on the line:
ctx.GetTable(type).InsertAllOnSubmit(entitesForSave);