Как сохранить значения textboxs в MVVM с помощью WPF

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я новичок в wpf и mvvm я пытался научиться использовать его сначала мне удалось показать список моего класса сотрудников очень хорошо , но когда я хочу добавить новый ( означает новый сотрудник), он сохраняет новую пустую запись в базе данных, я не знаю, как получить значение из textboxs. я много искал , но не могу понять, в чем моя проблема, так что могу ли я получить какую-либо помощь вот мой код

MY MODEL CLASS
    public class Employees 
    {

        #region Employee Members

        int _id;
        string _firstname;
        string _address;
        string _lastname;
        string _language;
        string _dob;
        string _nationality;
        string _gender;


        #endregion

        #region Members Properties

        Notify.NotifyUIBase n = new Notify.NotifyUIBase();

        public int ID
        {
            get { return _id; }
            set
            {
                _id = value;
            }
        }

        public string FirstName
        {
            get { return this._firstname; }
            set
            {
                if (value != this._firstname)
                {
                    this._firstname = value;
                    n.RaisePropertyChanged("FirstName");
                }
                
            }
        }

        public string Address
        {
            get { return _address; }
            set
            {
                _address = value;
                n.RaisePropertyChanged("Address");
            }
        }

        public string LastName
        {
            get { return _lastname; }
            set
            {
                _lastname = value;
                n.RaisePropertyChanged("LastName");
            }
        }

        public string Language
        {
            get { return _language; }
            set
            {
                _language = value;
                n.RaisePropertyChanged("Language");
            }
        }

        public string DOB
        {
            get { return _dob; }
            set
            {
                _dob = (value).ToString();
                n.RaisePropertyChanged("DOB");
            }
        }

        public string Nationality
        {
            get { return _nationality; }
            set
            {
                _nationality = value;
                n.RaisePropertyChanged("Nationality");
            }
        }

        public string Gender
        {
            get { return _gender; }
            set
            {
                _gender = value;
                n.RaisePropertyChanged("Gender");
            }
        }

        #endregion

    }

    MY NOTIFY CLASS  
    public class NotifyUIBase : INotifyPropertyChanged
        {
            public event PropertyChangedEventHandler PropertyChanged;
            public void RaisePropertyChanged([CallerMemberName] String propertyName = "")
            {
                if (PropertyChanged != null)
                {
                    PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
                }
            }
        }

    MY VIEWMODEL
    public class EditaEmployeesViewModel
    {
        #region Constructor

        public EditaEmployeesViewModel()
        {
            // intiales commands 
            NewEmployeeButton = new RelayCommand(OpenNewEmployee);
            UpdateEmployeeButton = new RelayCommand(UpdateEmployee);
            DeleteEmployeeButton = new RelayCommand(DeleteEmployee);

            SaveNewEmployeeButton = new RelayCommand(SaveNewEmployee);

        }

        #endregion

        #region Variables

        public RelayCommand NewEmployeeButton { get; set; }
        public RelayCommand UpdateEmployeeButton { get; set; }
        public RelayCommand DeleteEmployeeButton { get; set; }
        public RelayCommand SaveNewEmployeeButton { get; set; }

        private Model.Employees _EmployeeRecord;

        #endregion


        public Model.Employees EmployeeRecord
        {
            get
            {
                if (_EmployeeRecord == null)
                    return _EmployeeRecord = new Model.Employees();
                return _EmployeeRecord;
            }
            set
            {
                _EmployeeRecord = value;
                new Notify.NotifyUIBase().RaisePropertyChanged("EmployeeRecord");
            }
        }


        #region Adding New Employee

        #endregion

        #region Command Methods

        void OpenNewEmployee(object parameter)
        {
            View.AddUpdateEmployee aue = new View.AddUpdateEmployee();
            aue.Show();
        }

        void UpdateEmployee(object parameter)
        {

        }

        void DeleteEmployee(object parameter)
        {

        }

        void SaveNewEmployee(object parameter)
        {
            Model.Employees empp = EmployeeRecord;
            DataAccess.EmplyeeDatabaseLayer.InsertEmployee(empp);
        }
        #endregion

        #region get Employee List

        public ObservableCollection<Model.Employees> EmployeeList
        {
            get
            {
                ObservableCollection<Model.Employees> List = new ObservableCollection<Model.Employees>(DataAccess.EmplyeeDatabaseLayer.GetEmployeeFromDataBase());
                return List;
            }
        }
        #endregion
    }

    MY DATABASE CLASS
    public class EmplyeeDatabaseLayer
    {
        public static List<Model.Employees> GetEmployeeFromDataBase()
        {
            string sql = "select * from Employees";

            DataTable dt = DBConnections.SelectQuery(sql);
            var Employee = new List<Model.Employees>();

            foreach (DataRow row in dt.Rows)
            {
                var obj = new Model.Employees()
                {
                    ID = (int)row["id"],
                    FirstName = (string)row["FirstName"],
                    LastName = (string)row["LastName"],
                    DOB = (string)row["DOB"],
                    Gender = (string)row["Gender"],
                    Nationality = (string)row["Nationality"],
                    Language = ((string)row["Language"]),
                    Address = (string)row["Address"]
                };
                Employee.Add(obj);
            }
            return Employee;
        }

        internal static void InsertEmployee(Model.Employees employee)
        {
            try
            {
                string sql = "insert into Employees ([FirstName],[LastName],[Gender],[DOB],[Language],[Nationality],[Address]) values ";
                sql += "('" + employee.FirstName + "','" + employee.LastName + "','" + employee.Gender + "',";
                sql += "'" + employee.DOB + "','" + employee.Language + "','" + employee.Nationality + "'";
                sql += ",'" + employee.Address + "')";
                DBConnections.InserQuery(sql);

                MessageBox.Show("Data Saved Successfully.");
            }
            catch (SqlException ex)
            {
                throw ex;
            }
            finally
            {

            }
        }

        internal static void UpdateEmployee(Model.Employees employee)
        {
            try
            {
                string sql = "Update Employees set [FirstName]='" + employee.FirstName + "',[LastName]='" + employee.LastName + "',";
                sql += "[Gender] ='" + employee.Gender + "',[DOB]='" + employee.DOB + "',[Language]='" + employee.Language + "',";
                sql += "[Nationality]='" + employee.Nationality + "',[Address]='" + employee.Address + "' where [ID]='" + employee.ID + "'";

                DBConnections.UpdateQuery(sql);

                MessageBox.Show("Data Updated Successfully.");
            }
            catch (SqlException ex)
            {
                throw ex;
            }
            finally
            {

            }
        }

        internal static void DeleteEmployee(Model.Employees employee)
        {
            try
            {
                string sql = "Delete * from Employees where ID='" + employee.ID + "'";

                DBConnections.DeleteQuery(sql);

                MessageBox.Show("Data Deleted Successfully.");
            }
            catch (SqlException ex)
            {
                throw ex;
            }
            finally
            {

            }
        }
    }
    
<pre lang="text">MY VIEW ( SHOW EMPLOYEES LIST)
    
    <Window x:Class="EditaWPF01.NewTest.View.EmployeePage"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
        xmlns:local="clr-namespace:EditaWPF01.NewTest.View"
        xmlns:vm="clr-namespace:EditaWPF01.NewTest.ViewModel"
        mc:Ignorable="d"
        Title="Employees" Height="450" Width="800" 
       WindowStartupLocation="CenterScreen">

    <Window.DataContext>
        <vm:EditaEmployeesViewModel/>
    </Window.DataContext>

    <Grid>
        <GroupBox Header="Employees List" Margin="5">

            <Grid>
                <Grid.RowDefinitions>
                    <RowDefinition Height="27"/>
                    <RowDefinition Height="*"/>
                </Grid.RowDefinitions>

                <ToolBarTray >
                    <ToolBar >
                        <Button  x:Name="tlNewGas" ToolTip="New Gas" VerticalAlignment="Center" Padding="0" 
                                 Command="{Binding NewEmployeeButton}">
                            <Image Source=".\Pics\File_20px.png" />
                        </Button>
                        <Separator/>
                        <Button  x:Name="tlUpdateGas" ToolTip="Update Gas" VerticalAlignment="Center" Padding="0" 
                                 Command="{Binding UpdateEmployeeButton}">
                            <Image Source=".\Pics\Edit File_20px.png"/>
                        </Button>
                        <Separator/>
                        <Button x:Name="btnDelete" ToolTip="Delete Gas" VerticalAlignment="Center" Padding="0" 
                                Content="Delete" Command="{Binding DeleteEmployeeButton}"/>


                    </ToolBar>
                </ToolBarTray>
                <DataGrid Grid.Row="1" AutoGenerateColumns="False" ItemsSource="{Binding EmployeeList}" CanUserAddRows="False">
                    <DataGrid.Columns>
                        <DataGridTextColumn Header="F.Name" Binding="{Binding Path=FirstName}"/>
                        <DataGridTextColumn Header="L.Name" Binding="{Binding LastName}"/>
                        <DataGridTextColumn Header="Address" Binding="{Binding Address}"/>
                        <DataGridTextColumn Header="DOB" Binding="{Binding DOB}"/>
                        <DataGridTextColumn Header="Gender" Binding="{Binding Gender}"/>
                        <DataGridTextColumn Header="Nationality" Binding="{Binding Nationality}"/>
                        <DataGridTextColumn Header="Language" Binding="{Binding Language}"/>
                    </DataGrid.Columns>
                </DataGrid>
            </Grid>
        </GroupBox>
    </Grid>
</Window>


    MY FORM TO ADD NEW EMPLOYEE
    <Window x:Class="EditaWPF01.NewTest.View.AddUpdateEmployee"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
        xmlns:local="clr-namespace:EditaWPF01.NewTest.View"
        xmlns:vm="clr-namespace:EditaWPF01.NewTest.ViewModel"
        mc:Ignorable="d"
        Title="Add/Update Employee" Height="450" Width="500" WindowStartupLocation="CenterScreen">
    <Window.DataContext>
        <vm:EditaEmployeesViewModel/>
    </Window.DataContext>
    <Grid>
        <Grid.RowDefinitions>
            <RowDefinition Height="27"/>
            <RowDefinition Height="*"/>
        </Grid.RowDefinitions>

        <ToolBarTray Background="Orange">
            <ToolBar Background="Orange">
                <Button  x:Name="tlNewGas" ToolTip="New Gas" VerticalAlignment="Center" 
                         Padding="0" Content="Save" Height="27" Command="{Binding SaveNewEmployeeButton}"/>
            </ToolBar>
        </ToolBarTray>

            <Grid Grid.Row="1">
                <Grid.RowDefinitions>
                    <RowDefinition/>
                    <RowDefinition/>
                    <RowDefinition/>
                    <RowDefinition/>
                    <RowDefinition/>
                    <RowDefinition/>
                    <RowDefinition/>
                </Grid.RowDefinitions>

                <Grid.ColumnDefinitions>
                    <ColumnDefinition Width="150"/>
                    <ColumnDefinition/>
                </Grid.ColumnDefinitions>


            <TextBlock Text="First Name :" Grid.Row="0" Grid.Column="0" VerticalAlignment="Center" 
                       HorizontalAlignment="Center"/>
            <TextBox  Grid.Row="0" Grid.Column="1" VerticalAlignment="Center" 
                      Text="{Binding FirstName, UpdateSourceTrigger=Explicit}"/>
                              
            <TextBlock Text="Last Name :" Grid.Row="1" Grid.Column="0" VerticalAlignment="Center"
                         HorizontalAlignment="Center"/>
            <TextBox  Grid.Row="1" Grid.Column="1" VerticalAlignment="Center" 
                      Text="{Binding LastName, UpdateSourceTrigger=Explicit}"/>

            <TextBlock Text="Address :" Grid.Row="2" Grid.Column="0" VerticalAlignment="Center"
                       HorizontalAlignment="Center"/>
            <TextBox  Grid.Row="2" Grid.Column="1" VerticalAlignment="Center"
                      Text="{Binding Address, BindingGroupName=Group1, UpdateSourceTrigger=Explicit}"/>

            <TextBlock Text="DOB :" Grid.Row="3" Grid.Column="0" VerticalAlignment="Center"
                       HorizontalAlignment="Center"/>
            <TextBox  Grid.Row="3" Grid.Column="1" VerticalAlignment="Center"
                      Text="{Binding DOB, BindingGroupName=Group1, UpdateSourceTrigger=Explicit}"/>

            <TextBlock Text="Language :" Grid.Row="4" Grid.Column="0" VerticalAlignment="Center"
                       HorizontalAlignment="Center"/>
            <TextBox  Grid.Row="4" Grid.Column="1" VerticalAlignment="Center"
                      Text="{Binding Language, BindingGroupName=Group1, UpdateSourceTrigger=Explicit}"/>

            <TextBlock Text="Nationality :" Grid.Row="5" Grid.Column="0" VerticalAlignment="Center"
                       HorizontalAlignment="Center"/>
            <TextBox  Grid.Row="5" Grid.Column="1" VerticalAlignment="Center"
                      Text="{Binding Nationality, BindingGroupName=Group1, UpdateSourceTrigger=Explicit}"/>

            <TextBlock Text="Gender :" Grid.Row="6" Grid.Column="0" VerticalAlignment="Center"
                       HorizontalAlignment="Center"/>
            <TextBox  Grid.Row="6" Grid.Column="1" VerticalAlignment="Center"
                      Text="{Binding Gender, UpdateSourceTrigger=Explicit}"/>

        </Grid>

    </Grid>
</Window>

Что я уже пробовал:

я много искал , чтобы решить свою проблему, но я не могу найти решение, если есть проблема с моим кодом, пожалуйста, покажите мне

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