Add ValidateItemsAttribute.

Directory.Build.props

@@ -1,8 +1,8 @@
 <Project>
 
   <PropertyGroup>
-    <VersionPrefix>0.1.1</VersionPrefix>
-    <PackageValidationBaselineVersion>0.1.0</PackageValidationBaselineVersion>
+    <VersionPrefix>1.0.0</VersionPrefix>
+    <PackageValidationBaselineVersion>0.1.1</PackageValidationBaselineVersion>
     <LangVersion>12.0</LangVersion>
     <Nullable>enable</Nullable>
     <ImplicitUsings>enable</ImplicitUsings>

ReleaseNotes.md

@@ -1,5 +1,9 @@
 # Release Notes
 
+## 1.0.0
+
+* Add `ValidateItemsAttribute`.
+
 ## 0.1.1
 
 * Add .NET 6 target.

src/Faithlife.DataAnnotations/ValidateItemsAttribute.cs

@@ -0,0 +1,35 @@
+using System.Collections;
+using System.ComponentModel.DataAnnotations;
+
+namespace Faithlife.DataAnnotations;
+
+/// <summary>
+/// Used to validate a collection property whose items have their own properties with data annotations.
+/// </summary>
+[AttributeUsage(AttributeTargets.Property)]
+public sealed class ValidateItemsAttribute : ValidationAttribute
+{
+	/// <summary>
+	/// True if null items are allowed. Defaults to false.
+	/// </summary>
+	public bool AllowNullItems { get; set; }
+
+	/// <inheritdoc />
+	protected override ValidationResult? IsValid(object? value, ValidationContext validationContext)
+	{
+		if (value is not IEnumerable items)
+			return null;
+
+		var (validationResults, index) = items.Cast<object?>()
+			.Where(x => !AllowNullItems || x is not null)
+			.Select((x, i) => (Results: x is null ? [new ValidationResult("The item is null.")] : ValidatorUtility.GetValidationResults(x), Index: i))
+			.FirstOrDefault(x => x.Results.Count != 0);
+		if (validationResults is null)
+			return null;
+
+		var innerErrorMessage = string.Join(" ", validationResults.Select(x => x.ErrorMessage).Where(x => x is not null));
+		return new ValidationResult(
+			errorMessage: $"{FormatErrorMessage(validationContext.DisplayName)}{(innerErrorMessage.Length == 0 ? "" : $" ([{index}]: {innerErrorMessage})")}",
+			memberNames: validationContext.MemberName is { } memberName ? new[] { memberName } : null);
+	}
+}

tests/Faithlife.DataAnnotations.Tests/ValidateItemsAttributeTests.cs

@@ -0,0 +1,65 @@
+using System.ComponentModel.DataAnnotations;
+using NUnit.Framework;
+
+namespace Faithlife.DataAnnotations.Tests;
+
+public sealed class ValidateItemsAttributeTests
+{
+	[Test]
+	public void ValidateItems()
+	{
+		var validatable = new ValidatableDto { Required = "x" };
+
+		var results = ValidatorUtility.GetValidationResults(validatable);
+		Assert.That(results, Is.Empty);
+
+		validatable.Validatables = [null!];
+		results = ValidatorUtility.GetValidationResults(validatable);
+		Assert.That(results.Single().MemberNames.Single(), Is.EqualTo(nameof(ValidatableDto.Validatables)));
+		Assert.That(results.Single().ErrorMessage, Is.EqualTo("The field Validatables is invalid. ([0]: The item is null.)"));
+
+		validatable.Validatables = [new ValidatableDto(), new ValidatableDto()];
+		results = ValidatorUtility.GetValidationResults(validatable);
+		Assert.That(results.Single().MemberNames.Single(), Is.EqualTo(nameof(ValidatableDto.Validatables)));
+		Assert.That(results.Single().ErrorMessage, Is.EqualTo("The field Validatables is invalid. ([0]: The Required field is required.)"));
+
+		validatable.Validatables[0].Required = "x";
+		results = ValidatorUtility.GetValidationResults(validatable);
+		Assert.That(results.Single().MemberNames.Single(), Is.EqualTo(nameof(ValidatableDto.Validatables)));
+		Assert.That(results.Single().ErrorMessage, Is.EqualTo("The field Validatables is invalid. ([1]: The Required field is required.)"));
+
+		validatable.Validatables[1].Required = "x";
+		results = ValidatorUtility.GetValidationResults(validatable);
+		Assert.That(results, Is.Empty);
+	}
+
+	[Test]
+	public void ValidateNullableItems()
+	{
+		var validatable = new ValidatableDto { Required = "x" };
+
+		var results = ValidatorUtility.GetValidationResults(validatable);
+		Assert.That(results, Is.Empty);
+
+		validatable.NullableValidatables = [null!];
+		results = ValidatorUtility.GetValidationResults(validatable);
+		Assert.That(results, Is.Empty);
+
+		validatable.Validatables = [new ValidatableDto()];
+		results = ValidatorUtility.GetValidationResults(validatable);
+		Assert.That(results.Single().MemberNames.Single(), Is.EqualTo(nameof(ValidatableDto.Validatables)));
+		Assert.That(results.Single().ErrorMessage, Is.EqualTo("The field Validatables is invalid. ([0]: The Required field is required.)"));
+	}
+
+	private sealed class ValidatableDto
+	{
+		[Required]
+		public string? Required { get; set; }
+
+		[ValidateItems]
+		public IReadOnlyList<ValidatableDto>? Validatables { get; set; }
+
+		[ValidateItems(AllowNullItems = true)]
+		public IReadOnlyList<ValidatableDto?>? NullableValidatables { get; set; }
+	}
+}