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POCannot add values to local database in windows phone app
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  1. POCannot add values to local database in windows phone app
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    copied!<p>I am trying to create a database app for Windows Phone 8. When I try to add a new table entry in one of the tables of the DB, I get an error like this.</p> <pre><code> {System.InvalidCastException: Could not convert from type 'System.Byte[]' to type 'System.String'. at System.Data.Linq.DBConvert.ChangeType(Object value, Type type) at System.Data.Linq.ChangeDirector.StandardChangeDirector.DoResultSetAutoSync(TrackedObject item) at System.Data.Linq.ChangeDirector.StandardChangeDirector.DoResultSetInsert(TrackedObject item) at System.Data.Linq.ChangeDirector.StandardChangeDirector.Insert(TrackedObject item) at System.Data.Linq.ChangeProcessor.SubmitChanges(ConflictMode failureMode) at System.Data.Linq.DataContext.SubmitChanges(ConflictMode failureMode) at System.Data.Linq.DataContext.SubmitChanges() at CygnusModel.ViewModel.CygnusViewModel.AddNewSem(CygSem NewCygSem) at Cygnus.AddSemView.Save_sem(Object sender, EventArgs e) at Microsoft.Phone.Shell.ApplicationBarItemContainer.FireEventHandler(EventHandler handler, Object sender, EventArgs args) at Microsoft.Phone.Shell.ApplicationBarIconButtonContainer.ClickEvent() at Microsoft.Phone.Shell.ApplicationBar.OnCommand(UInt32 idCommand, Boolean isButton) at Microsoft.Phone.Shell.Interop.NativeCallbackInteropWrapper.OnCommand(UInt32 idCommand, Boolean isButton)} </code></pre> <p>This is the code I used</p> <pre><code>if (CygSemName.Text.Length &gt; 0) { CygSem NewCygSem = new CygSem { SemName = (string)CygSemName.Text, SemStart = (DateTime)CygSemStart.Value, SemEnd = (DateTime)CygSemEnd.Value }; App.ViewModel.AddNewSem(NewCygSem); if (NavigationService.CanGoBack) { NavigationService.GoBack(); } </code></pre> <p>Could some one help me with this? Please keep in mind that, I am new in c# and Windows Phone development.</p> <p>ViewModel:</p> <pre><code>using System.Collections.Generic; using System.Collections.ObjectModel; using System.ComponentModel; using System.Linq; //Includes DataModel Classes using CygnusModel.Model; namespace CygnusModel.ViewModel { public class CygnusViewModel : INotifyPropertyChanged { private CygDataContext CygDb; //Class Constructor Creating the connection between Model &amp; View public CygnusViewModel(string CygDataConnectionString) { CygDb = new CygDataContext(CygDataConnectionString); } //Save changing Method private void CygSaveChanges() { CygDb.SubmitChanges(); } //Contains Change tracking INotify Events #region INotifies public event PropertyChangedEventHandler PropertyChanged; private void NotifyPropertyChanged(string propertyName) { if (PropertyChanged != null) { PropertyChanged(this, new PropertyChangedEventArgs(propertyName)); } } #endregion //All The Semesters private ObservableCollection&lt;CygSem&gt; _allSems; public ObservableCollection&lt;CygSem&gt; AllSems { get { return _allSems; } set { _allSems = value; NotifyPropertyChanged("AllSems"); } } //All The Subjects private ObservableCollection&lt;CygSubs&gt; _allSubs; public ObservableCollection&lt;CygSubs&gt; AllSubs { get { return _allSubs; } set { _allSubs = value; NotifyPropertyChanged("AllSubs"); } } //All The Lectures private ObservableCollection&lt;CygLect&gt; _allLects; public ObservableCollection&lt;CygLect&gt; AllLects { get { return _allLects; } set { _allLects = value; NotifyPropertyChanged("AllLects"); } } //All The Exams private ObservableCollection&lt;CygExam&gt; _allExam; public ObservableCollection&lt;CygExam&gt; AllExam { get { return _allExam; } set { _allExam = value; NotifyPropertyChanged("AllExam"); } } //All The Instructors private ObservableCollection&lt;CygInst&gt; _allInsts; public ObservableCollection&lt;CygInst&gt; AllInsts { get { return _allInsts; } set { _allInsts = value; NotifyPropertyChanged("AllInsts"); } } //All The Holidays private ObservableCollection&lt;CygHoli&gt; _allHolis; public ObservableCollection&lt;CygHoli&gt; AllHolis { get { return _allHolis; } set { _allHolis = value; NotifyPropertyChanged("AllHolis"); } } //All the lectures of today private ObservableCollection&lt;CygLect&gt; _todayLect; public ObservableCollection&lt;CygLect&gt; TodayLect { get { return _todayLect; } set { _todayLect = value; NotifyPropertyChanged("TodayLect"); } } //All the Exams of today private ObservableCollection&lt;CygExam&gt; _todayExam; public ObservableCollection&lt;CygExam&gt; TodayExam { get { return _todayExam; } set { _todayExam = value; NotifyPropertyChanged("TodayExam"); } } // Query database and load the all the data public void LoadAllAvailables() { } //Query DB and load all the semester public void LoadAllSems() { var Sems = from CygSem semes in CygDb.Semesters select semes; AllSems = new ObservableCollection&lt;CygSem&gt;(Sems); } //Query DB and load all Holidays public void LoadAllHolis() { var Holis = from CygHoli holid in CygDb.Holidays select holid; AllHolis = new ObservableCollection&lt;CygHoli&gt;(Holis); } //Query DB and load Subjects based on Semester public void LoadSemBasedSubs() { } //Query DB and load all the Lectures and exams per day public void LoadForTheDay() { } //Query the DB and load Lectures and Exams per Subject public void LoadForTheSub() { } //Add New Sem public void AddNewSem(CygSem NewCygSem) { CygDb.Semesters.InsertOnSubmit(NewCygSem); CygDb.SubmitChanges(); AllSems.Add(NewCygSem); } //Add New Holiday public void AddNewHoli(CygHoli NewCygHoli) { CygDb.Holidays.InsertOnSubmit(NewCygHoli); CygDb.SubmitChanges(); } } } </code></pre> <p>Model:</p> <pre><code>//Semester Class [Table] public class CygSem : INotifyPropertyChanging, INotifyPropertyChanged { //_version variable. Binary Datatype [Column(IsVersion = true)] private string _version; //Contains Change tracking INotify Events #region INotifies public event PropertyChangedEventHandler PropertyChanged; private void NotifyPropertyChanged(string PropertyName) { if (PropertyChanged != null) { PropertyChanged(this, new PropertyChangedEventArgs(PropertyName)); } } public event PropertyChangingEventHandler PropertyChanging; private void NotifyPropertyChanging(string PropertyName) { if (PropertyChanging != null) { PropertyChanging(this, new PropertyChangingEventArgs(PropertyName)); } } #endregion //Semester ID Variable private int _semID; [Column(IsPrimaryKey = true, IsDbGenerated = true, DbType = "INT NOT NULL Identity", CanBeNull = false, AutoSync = AutoSync.OnInsert)] public int SemID { get { return _semID; } set { NotifyPropertyChanging("SemID"); _semID = value; NotifyPropertyChanged("SemID"); } } ////Semester Name //private string _semName; //[Column] //public string SemName //{ // get // { // return _semName.ToString(); // } // set // { // NotifyPropertyChanging("SemName"); // _semName = value.ToString(); // NotifyPropertyChanged("SemName"); // } //} //Semester Start Date private DateTime _semStart; [Column] public DateTime SemStart { get { return _semStart; } set { NotifyPropertyChanging("SemStart"); _semStart = value; NotifyPropertyChanged("SemStart"); } } //Semester End Date private DateTime _semEnd; [Column] public DateTime SemEnd { get { return _semEnd; } set { NotifyPropertyChanging("SemEnd"); _semEnd = value; NotifyPropertyChanged("SemEnd"); } } #region Subject Set // Define the entity set for the collection side of the relationship. private EntitySet&lt;CygSubs&gt; _subs; [Association(Storage = "_subs", OtherKey = "_cygSemID", ThisKey = "SemID")] public EntitySet&lt;CygSubs&gt; Subs { get { return this._subs; } set { this._subs.Assign(value); } } // Assign handlers for the add and remove operations, respectively. public CygSem() { _subs = new EntitySet&lt;CygSubs&gt;( new Action&lt;CygSubs&gt;(this.attach_sem), new Action&lt;CygSubs&gt;(this.dettach_sem) ); } // Called during an add operation private void attach_sem(CygSubs _subj) { NotifyPropertyChanging("CygSubs"); _subj.Semester = this; } // Called during a remove operation private void dettach_sem(CygSubs _subj) { NotifyPropertyChanging("CygSubs"); _subj.Semester = null; } #endregion } </code></pre> <p>DataContext:</p> <pre><code>[Database] public class CygDataContext : DataContext { //Pass The Connection String to the base class. public CygDataContext(string ConnectionString) : base(ConnectionString) { } //Specify table Semesters public Table&lt;CygSem&gt; Semesters; //Specify table Subjects public Table&lt;CygSubs&gt; Subjects; //Specify table Lecture public Table&lt;CygLect&gt; Lectures; //Specify table Exams public Table&lt;CygExam&gt; Exams; //Specify table Instructors public Table&lt;CygInst&gt; Insts; //Specify table Holidays public Table&lt;CygHoli&gt; Holidays; } </code></pre>
 

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