Generate INSERT SQL for Entity LINQ2SQL without ID

private string GenerateInsertStatementForEntity(object entity)
{
    Type entityType = entity.GetType();
    string tableName = ((TableAttribute)entityType.GetCustomAttributes(false)[0]).Name;

    var dict = new Dictionary<string, object>();
    foreach (var property in entityType.GetProperties())
    {
        var attributes = property.GetCustomAttributes(typeof(ColumnAttribute), false);
        if (attributes != null && attributes.Length != 0)
        {
            ColumnAttribute colAttr = (ColumnAttribute)attributes[0];
            string colName = colAttr.Name ?? property.Name;
            string value = property.GetValue(entity, null);

            dict[colName] = value;
        }
    }

    var keysStrs = dict.Keys.Select(k => String.Format("{0}", k));
    var valuesStrs = new List<string>();
    foreach (var key in dict.Keys)
    {
        object value = dict[key];
        if (value == null)
        {
            valuesStrs.Add("null");
        }
        else if (value is string)
        {
            valuesStrs.Add(String.Format("'{0}'", value));
        }
        else
        {
            valuesStrs.Add(value.ToString());
        }
    }

    return String.Format("INSERT INTO {0}({1}) VALUES ({2})",
        tableName,
        String.Join(",", keysStrs.ToArray()),
        String.Join(",", valuesStrs.ToArray()));
}