Fix usage of whitespace IDs when TId is string

src/JsonApiDotNetCore/Controllers/JsonApiController.cs

@@ -51,15 +51,15 @@ public override async Task<IActionResult> GetAsync(CancellationToken cancellatio
     /// <inheritdoc />
     [HttpGet("{id}")]
     [HttpHead("{id}")]
-    public override async Task<IActionResult> GetAsync([Required] [DisallowNull] TId id, CancellationToken cancellationToken)
+    public override async Task<IActionResult> GetAsync([Required(AllowEmptyStrings = true)] [DisallowNull] TId id, CancellationToken cancellationToken)
     {
         return await base.GetAsync(id, cancellationToken);
     }
 
     /// <inheritdoc />
     [HttpGet("{id}/{relationshipName}")]
     [HttpHead("{id}/{relationshipName}")]
-    public override async Task<IActionResult> GetSecondaryAsync([Required] [DisallowNull] TId id, [Required] string relationshipName,
+    public override async Task<IActionResult> GetSecondaryAsync([Required(AllowEmptyStrings = true)] [DisallowNull] TId id, [Required] string relationshipName,
         CancellationToken cancellationToken)
     {
         return await base.GetSecondaryAsync(id, relationshipName, cancellationToken);
@@ -68,8 +68,8 @@ public override async Task<IActionResult> GetSecondaryAsync([Required] [Disallow
     /// <inheritdoc />
     [HttpGet("{id}/relationships/{relationshipName}")]
     [HttpHead("{id}/relationships/{relationshipName}")]
-    public override async Task<IActionResult> GetRelationshipAsync([Required] [DisallowNull] TId id, [Required] string relationshipName,
-        CancellationToken cancellationToken)
+    public override async Task<IActionResult> GetRelationshipAsync([Required(AllowEmptyStrings = true)] [DisallowNull] TId id,
+        [Required] string relationshipName, CancellationToken cancellationToken)
     {
         return await base.GetRelationshipAsync(id, relationshipName, cancellationToken);
     }
@@ -83,39 +83,41 @@ public override async Task<IActionResult> PostAsync([Required] TResource resourc
 
     /// <inheritdoc />
     [HttpPost("{id}/relationships/{relationshipName}")]
-    public override async Task<IActionResult> PostRelationshipAsync([Required] [DisallowNull] TId id, [Required] string relationshipName,
-        [Required] ISet<IIdentifiable> rightResourceIds, CancellationToken cancellationToken)
+    public override async Task<IActionResult> PostRelationshipAsync([Required(AllowEmptyStrings = true)] [DisallowNull] TId id,
+        [Required] string relationshipName, [Required] ISet<IIdentifiable> rightResourceIds, CancellationToken cancellationToken)
     {
         return await base.PostRelationshipAsync(id, relationshipName, rightResourceIds, cancellationToken);
     }
 
     /// <inheritdoc />
     [HttpPatch("{id}")]
-    public override async Task<IActionResult> PatchAsync([Required] [DisallowNull] TId id, [Required] TResource resource, CancellationToken cancellationToken)
+    public override async Task<IActionResult> PatchAsync([Required(AllowEmptyStrings = true)] [DisallowNull] TId id, [Required] TResource resource,
+        CancellationToken cancellationToken)
     {
         return await base.PatchAsync(id, resource, cancellationToken);
     }
 
     /// <inheritdoc />
     [HttpPatch("{id}/relationships/{relationshipName}")]
+    // `AllowEmptyStrings = true` in `[Required]` prevents the model binder from producing a validation error on whitespace when TId is string.
     // Parameter `[Required] object? rightValue` makes Swashbuckle generate the OpenAPI request body as required. We don't actually validate ModelState, so it doesn't hurt.
-    public override async Task<IActionResult> PatchRelationshipAsync([Required] [DisallowNull] TId id, [Required] string relationshipName,
-        [Required] object? rightValue, CancellationToken cancellationToken)
+    public override async Task<IActionResult> PatchRelationshipAsync([Required(AllowEmptyStrings = true)] [DisallowNull] TId id,
+        [Required] string relationshipName, [Required] object? rightValue, CancellationToken cancellationToken)
     {
         return await base.PatchRelationshipAsync(id, relationshipName, rightValue, cancellationToken);
     }
 
     /// <inheritdoc />
     [HttpDelete("{id}")]
-    public override async Task<IActionResult> DeleteAsync([Required] [DisallowNull] TId id, CancellationToken cancellationToken)
+    public override async Task<IActionResult> DeleteAsync([Required(AllowEmptyStrings = true)] [DisallowNull] TId id, CancellationToken cancellationToken)
     {
         return await base.DeleteAsync(id, cancellationToken);
     }
 
     /// <inheritdoc />
     [HttpDelete("{id}/relationships/{relationshipName}")]
-    public override async Task<IActionResult> DeleteRelationshipAsync([Required] [DisallowNull] TId id, [Required] string relationshipName,
-        [Required] ISet<IIdentifiable> rightResourceIds, CancellationToken cancellationToken)
+    public override async Task<IActionResult> DeleteRelationshipAsync([Required(AllowEmptyStrings = true)] [DisallowNull] TId id,
+        [Required] string relationshipName, [Required] ISet<IIdentifiable> rightResourceIds, CancellationToken cancellationToken)
     {
         return await base.DeleteRelationshipAsync(id, relationshipName, rightResourceIds, cancellationToken);
     }

test/JsonApiDotNetCoreTests/IntegrationTests/ZeroKeys/EmptyGuidAsKeyTests.cs

@@ -572,9 +572,9 @@ await _testContext.RunOnDatabaseAsync(async dbContext =>
 
         await _testContext.RunOnDatabaseAsync(async dbContext =>
         {
-            Map? gameInDatabase = await dbContext.Maps.FirstWithIdOrDefaultAsync(existingMap.Id);
+            Map? mapInDatabase = await dbContext.Maps.FirstWithIdOrDefaultAsync(existingMap.Id);
 
-            gameInDatabase.Should().BeNull();
+            mapInDatabase.Should().BeNull();
         });
     }
 }

test/JsonApiDotNetCoreTests/IntegrationTests/ZeroKeys/Game.cs

@@ -17,6 +17,9 @@ public sealed class Game : Identifiable<int?>
     [Attr]
     public Guid SessionToken => Guid.NewGuid();
 
+    [HasOne]
+    public Player? Host { get; set; }
+
     [HasMany]
     public ICollection<Player> ActivePlayers { get; set; } = new List<Player>();
 

test/JsonApiDotNetCoreTests/IntegrationTests/ZeroKeys/Player.cs

@@ -1,11 +1,12 @@
 using JetBrains.Annotations;
+using JsonApiDotNetCore.Configuration;
 using JsonApiDotNetCore.Resources;
 using JsonApiDotNetCore.Resources.Annotations;
 
 namespace JsonApiDotNetCoreTests.IntegrationTests.ZeroKeys;
 
 [UsedImplicitly(ImplicitUseTargetFlags.Members)]
-[Resource(ControllerNamespace = "JsonApiDotNetCoreTests.IntegrationTests.ZeroKeys")]
+[Resource(ControllerNamespace = "JsonApiDotNetCoreTests.IntegrationTests.ZeroKeys", ClientIdGeneration = ClientIdGenerationMode.Allowed)]
 public sealed class Player : Identifiable<string?>
 {
     [Attr]