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C# WPF datagrid not persisting inserts

I am working with VS 2022 and trying to make a WPF MVVM application. The application updates the items displayed in the datagrid, persisting the changes to the database upon save. However, adding a new record to the grid does not insert (without extra steps). I imagine I am missing something simple.

It seems to me as if since the updates persist from the ObservableCollection to the context without extra coding then the inserts would also.

View:

    <Window x:Class="PictureWar.View.TagTagTypeWindow"
        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:PictureWar.View"
        mc:Ignorable="d"
        Title="Tags and TagTypes" Height="450" Width="800">
    <Window.Resources>
        <CollectionViewSource x:Key="tagTypeViewSource" Source="{Binding TagTypes}"/>
        <CollectionViewSource x:Key="tagTagTypesViewSource" 
                              Source="{Binding Tags, Source={StaticResource tagTypeViewSource}}"/>
    </Window.Resources>
    <Grid>
        <Grid.ColumnDefinitions>
            <ColumnDefinition Width="*" />
            <ColumnDefinition Width="*" />
        </Grid.ColumnDefinitions>
        <Grid.RowDefinitions>
            <RowDefinition Height="Auto" />
            <RowDefinition Height="*" />
            <RowDefinition Height="Auto" />
        </Grid.RowDefinitions>
        <DataGrid Grid.Row="0" Grid.Column="0" x:Name="tagTypesDataGrid" AutoGenerateColumns="False" 
          EnableRowVirtualization="True" 
          ItemsSource="{Binding Source={StaticResource tagTypeViewSource}}" 
          Margin="0,0,0,0" RowDetailsVisibilityMode="VisibleWhenSelected">
            <DataGrid.Columns>
                <DataGridTextColumn Binding="{Binding ID}"
                                    Header="Tag Type Id" 
                                    Width="SizeToHeader"
                                    IsReadOnly="True"/>
                <DataGridTextColumn Binding="{Binding Name}" 
                                    Header="Name" 
                                    Width="*"/>
            </DataGrid.Columns>
        </DataGrid>
        
        <DataGrid Grid.Row="0" Grid.Column="1" x:Name="tagsDataGrid" AutoGenerateColumns="False" 
          EnableRowVirtualization="True" 
          ItemsSource="{Binding Source={StaticResource tagTagTypesViewSource}}" 
          Margin="0,0,0,0" RowDetailsVisibilityMode="VisibleWhenSelected" 
          RenderTransformOrigin="0.488,0.251">
            <DataGrid.Columns>
                <DataGridTextColumn Binding="{Binding ID}" 
                                    Header="Tag Id" 
                                    Width="SizeToHeader" 
                                    IsReadOnly="True"/>
                <DataGridTextColumn Binding="{Binding TagTypeID}" 
                                    Header="Tag Type Id" 
                                    Width="SizeToHeader"
                                    IsReadOnly="False"/>
                <DataGridTextColumn Binding="{Binding Name}" Header="Name" Width="*"/>
            </DataGrid.Columns>
        </DataGrid>
        
        <Button Grid.Row="2" Grid.ColumnSpan="2" Command="{Binding SaveCommand}">Save</Button>
    </Grid>
</Window>

Code Behind

    public partial class TagTagTypeWindow : Window
    {
        public TagTagTypeWindow()
        {
            InitializeComponent();
            DataContext = new TagTagTypeViewModel();
        }
    }

View Model

    namespace PictureWar.ViewModel;

    public class TagTagTypeViewModel : ObservableObject
    {
        private ObservableCollection<TagType> _tagTypes;
        private readonly TagTypeRepository _repository;

        public TagTagTypeViewModel()
        {
            _repository = new TagTypeRepository();
            _tagTypes = new ObservableCollection<TagType>(_repository.GetAllTagTypes().ToList());
            SaveCommand = new RelayCommand(DoSave);
        }

        public IRelayCommand SaveCommand { get; }

        public ObservableCollection<TagType> TagTypes
        {
            get => _tagTypes;
            set { SetProperty(ref _tagTypes, value); }
        }

        public void DoSave()
        {
            var newTagTypes = TagTypes.Where(tt => tt.ID < 1); //extra step
            _repository.SaveAllTagTypes(newTagTypes);
        }
    }

Repository

    public class TagTypeRepository
    {
        private readonly WarContext _context;

        public TagTypeRepository()
        {
            _context = new WarContext();
        }

        public IEnumerable<TagType> GetAllTagTypes()
        {
            return _context.TagType.Include(tt => tt.Tags);
        }

        public void SaveAllTagTypes(IEnumerable<TagType> newTagTypes)
        {
            _context.TagType.AddRange(newTagTypes); //part of the extra step
            _context.SaveChanges();
        }
    }