Marked core view model properties as not-nullable, required

In a typical use case, all properties will be set to their defaults when a view model is initialized. Given this, the return type of otherwise required properties must be nullable. The mapping service will then immediately populate these, however, and thus we never expect them to _actually_ be null. As such, we can annotate them with the `[NotNull]` attribute to assure callers that, in practice, they're not null, and the `[DisallowNull]` attribute to dissuade callers from setting them to null.

In addition, there are no scenarios where we expect most of these values to even have empty values. As such, we can mark them as `[Required]` to help enforce their use. This is critical for binding models, where we want to ensure that the interface isn't simply satisfied, but also that data is populated. For instance, a `ITopicBindingModel` without `Key` or `ContentType` values defined isn't especially useful.

Given that, most required properties have been annotated as `[Required, NotNull, DisallowNull]`.

Author: JeremyCaney

OnTopic.Tests/BindingModels/BasicTopicBindingModel.cs

@@ -4,6 +4,7 @@
 | Project       Topics Library
 \=============================================================================================================================*/
 using System.ComponentModel.DataAnnotations;
+using System.Diagnostics.CodeAnalysis;
 using OnTopic.Models;
 
 namespace OnTopic.Tests.BindingModels {
@@ -21,14 +22,15 @@ public class BasicTopicBindingModel : ITopicBindingModel {
 
     public BasicTopicBindingModel() { }
 
-    public BasicTopicBindingModel(string? key, string? contentType) {
+    public BasicTopicBindingModel(string key, string contentType) {
       Key = key;
       ContentType = contentType;
     }
 
+    [Required, NotNull, DisallowNull]
     public string? Key { get; init; }
 
-    [Required]
+    [Required, NotNull, DisallowNull]
     public string? ContentType { get; init; }
 
   } //Class

OnTopic.Tests/BindingModels/RecordTopicBindingModel.cs

@@ -4,6 +4,7 @@
 | Project       Topics Library
 \=============================================================================================================================*/
 using System.ComponentModel.DataAnnotations;
+using System.Diagnostics.CodeAnalysis;
 using OnTopic.Models;
 
 namespace OnTopic.Tests.BindingModels {
@@ -22,9 +23,10 @@ public class RecordTopicBindingModel : ITopicBindingModel {
 
     public RecordTopicBindingModel() { }
 
+    [Required, NotNull, DisallowNull]
     public string? Key { get; init; }
 
-    [Required]
+    [Required, NotNull, DisallowNull]
     public string? ContentType { get; init; }
 
   } //Class

OnTopic.ViewModels/BindingModels/AssociatedTopicBindingModel.cs

@@ -4,6 +4,7 @@
 | Project       Topics Library
 \=============================================================================================================================*/
 using System.ComponentModel.DataAnnotations;
+using System.Diagnostics.CodeAnalysis;
 using OnTopic.Mapping.Reverse;
 using OnTopic.Models;
 
@@ -32,7 +33,7 @@ public record AssociatedTopicBindingModel : IAssociatedTopicBindingModel {
     /// <requires description="The value from the getter must not be null." exception="T:System.ArgumentNullException">
     ///   value is not null
     /// </requires>
-    [Required]
+    [Required, NotNull, DisallowNull]
     public string? UniqueKey { get; init; }
 
   } //Class

OnTopic.ViewModels/NavigationTopicViewModel.cs

@@ -5,6 +5,8 @@
 \=============================================================================================================================*/
 using System;
 using System.Collections.ObjectModel;
+using System.ComponentModel.DataAnnotations;
+using System.Diagnostics.CodeAnalysis;
 using OnTopic.Models;
 
 namespace OnTopic.ViewModels {
@@ -34,6 +36,7 @@ public sealed record NavigationTopicViewModel : INavigationTopicViewModel<Naviga
     | TITLE
     \-------------------------------------------------------------------------------------------------------------------------*/
     /// <inheritdoc cref="TopicViewModel"/>
+    [Required, NotNull, DisallowNull]
     public string? Title { get; init; }
 
     /*==========================================================================================================================
@@ -48,6 +51,7 @@ public sealed record NavigationTopicViewModel : INavigationTopicViewModel<Naviga
     | WEB PATH
     \-------------------------------------------------------------------------------------------------------------------------*/
     /// <inheritdoc cref="WebPath"/>
+    [Required, NotNull, DisallowNull]
     public string? WebPath { get; init; }
 
     /*==========================================================================================================================

OnTopic.ViewModels/TopicViewModel.cs

@@ -4,6 +4,8 @@
 | Project       Topics Library
 \=============================================================================================================================*/
 using System;
+using System.ComponentModel.DataAnnotations;
+using System.Diagnostics.CodeAnalysis;
 using OnTopic.Mapping.Annotations;
 using OnTopic.Models;
 
@@ -32,24 +34,28 @@ public record TopicViewModel: ITopicViewModel, IKeyedTopicViewModel, IAssociated
     | KEY
     \-------------------------------------------------------------------------------------------------------------------------*/
     /// <inheritdoc />
+    [Required, NotNull, DisallowNull]
     public string? Key { get; init; }
 
     /*==========================================================================================================================
     | CONTENT TYPE
     \-------------------------------------------------------------------------------------------------------------------------*/
     /// <inheritdoc />
+    [Required, NotNull, DisallowNull]
     public string? ContentType { get; init; }
 
     /*==========================================================================================================================
     | UNIQUE KEY
     \-------------------------------------------------------------------------------------------------------------------------*/
     /// <inheritdoc />
+    [Required, NotNull, DisallowNull]
     public string? UniqueKey { get; init; }
 
     /*==========================================================================================================================
     | WEB PATH
     \-------------------------------------------------------------------------------------------------------------------------*/
     /// <inheritdoc />
+    [Required, NotNull, DisallowNull]
     public string? WebPath { get; init; }
 
     /*==========================================================================================================================
@@ -62,6 +68,7 @@ public record TopicViewModel: ITopicViewModel, IKeyedTopicViewModel, IAssociated
     | TITLE
     \-------------------------------------------------------------------------------------------------------------------------*/
     /// <inheritdoc />
+    [Required, NotNull, DisallowNull]
     public string? Title { get; init; }
 
     /*==========================================================================================================================

OnTopic/Models/IAssociatedTopicBindingModel.cs

@@ -4,6 +4,7 @@
 | Project       Topics Library
 \=============================================================================================================================*/
 using System.ComponentModel.DataAnnotations;
+using System.Diagnostics.CodeAnalysis;
 using OnTopic.Mapping.Reverse;
 
 namespace OnTopic.Models {
@@ -30,7 +31,7 @@ public interface IAssociatedTopicBindingModel {
     /// <requires description="The value from the getter must not be null." exception="T:System.ArgumentNullException">
     ///   value is not null
     /// </requires>
-    [Required]
+    [Required, NotNull, DisallowNull]
     string? UniqueKey { get; init; }
 
   } //Class

OnTopic/Models/ITopicBindingModel.cs

@@ -4,6 +4,7 @@
 | Project       Topics Library
 \=============================================================================================================================*/
 using System.ComponentModel.DataAnnotations;
+using System.Diagnostics.CodeAnalysis;
 using OnTopic.Mapping.Reverse;
 using OnTopic.Metadata;
 
@@ -31,7 +32,7 @@ public interface ITopicBindingModel: IKeyedTopicViewModel {
     ///   Each topic is associated with a content type. The content type determines which attributes are displayed in the Topics
     ///   Editor (via the <see cref="ContentTypeDescriptor.AttributeDescriptors"/> property).
     /// </remarks>
-    [Required]
+    [Required, NotNull, DisallowNull]
     string? ContentType { get; init; }
 
   } //Class

OnTopic/Models/ITopicViewModel.cs

@@ -3,8 +3,10 @@
 | Client        Ignia, LLC
 | Project       Topics Library
 \=============================================================================================================================*/
+using System;
+using System.ComponentModel.DataAnnotations;
+using System.Diagnostics.CodeAnalysis;
 using OnTopic.Mapping;
-using OnTopic.Metadata;
 
 namespace OnTopic.Models {
 
@@ -45,6 +47,7 @@ public interface ITopicViewModel: IKeyedTopicViewModel, IAssociatedTopicBindingM
     ///   Gets or sets the topic's <see cref="WebPath"/> attribute, which represents the <see cref="IAssociatedTopicBindingModel
     ///   .UniqueKey"/> in its URL format.
     /// </summary>
+    [Required, NotNull, DisallowNull]
     string? WebPath { get; init; }
 
     /*==========================================================================================================================
@@ -82,6 +85,7 @@ public interface ITopicViewModel: IKeyedTopicViewModel, IAssociatedTopicBindingM
     ///   restrictions on what characters can be used in the title. For this reason, it provides the default public value for
     ///   referencing topics.
     /// </remarks>
+    [Required, NotNull, DisallowNull]
     string? Title { get; init; }
 
   } //Class