DataGrid <-> ObservableCollection中的MVVM唯一列

Question

My apologies if this question has been answered already. I've been struggling to figure out how to implement this and Google/StackOverflow searches haven't given me an answer that fits my needs. To provide context to stuff like BindableBase -> I'm using Prism WPF 7.1

Model:

public class SampleModel : BindableBase
{
    private string _id;
    public string ID
    {
        get => _id;
        set => SetProperty(ref _id, value);
    }

    public string _name;
    public string Name
    {
        get => _name;
        set => SetProperty(ref _name, value);
    }

    public SampleModel()
    {
        ID = string.Empty;
        Name = string.Empty;
    }
}

View Model:

public class SampleViewModel
{
    public ObservableCollection<SampleModel> Collection { get; set; }

    public SampleModel SelectedEntry { get; set; }        

    public MainViewModel()
    {
        Collection = new ObservableCollection<SampleModel>();
    }
}

View:

<DataGrid Grid.Row="0"
        AutoGenerateColumns="False"
        ItemsSource="{Binding Collection}"
        SelectedItem="{Binding SelectedEntry}">
<DataGrid.Columns>
    <DataGridTextColumn Binding="{Binding ID, UpdateSourceTrigger=PropertyChanged, ValidatesOnDataErrors=True}"
                        Header="ID"
                        Width="*"/>
    <DataGridTextColumn Binding="{Binding Name}"
                        Header="Name"
                        Width="*"/>
</DataGrid.Columns>

I would like to ensure that the cells of the WPF DataGrid goes red if the ID isn't unique.

The only solution I can think right now would be to add a pointer to the Collection<SampleModel> to every SampleModel instance, have SampleModel implement INotifyDataErrorInfo , and iterate looking for duplicate during System.ComponentModel.DataAnnotations.Validator.TryValidateProperty() (using a custom UniqueAttribute ). However I'm worried that this wouldn't be the right solution since the Model would be coupled to the Collection that contains it.

public class UniqueAttribute : ValidationAttribute
{
    protected override ValidationResult IsValid(object value, ValidationContext validationContext)
    {
        // Validate that property does not exist in collection?
    }
}

Does anyone know of a better way of implementing this?

Answer 1

IMHO the best way to enforce uniqueness is to let the database do it. ID sounds like the primary key of your table, so the database will throw an exception if you try to create a duplicate. Catch the error and turn it into a user friendly validation message.

If you rely on your UI, you run the risk of two users creating the same ID.