Add maximum length validator.

Author: CodingFlow

CodingFlow.FluentValidation.UnitTests/MaximumLengthValidatorTests.cs

@@ -0,0 +1,36 @@
+using CodingFlow.FluentValidation.Validators;
+using FluentAssertions;
+using static CodingFlow.FluentValidation.Validations;
+
+namespace CodingFlow.FluentValidation.UnitTests;
+
+public class MaximumLengthValidatorTests
+{
+    [TestCase("short")]
+    public void MaximumLength_Valid(string input)
+    {
+        var result = RuleFor(input)
+            .MaximumLength(5)
+            .Result();
+
+        result.Should().BeEquivalentTo(new ValidationResult
+        {
+            IsValid = true,
+            Errors = []
+        });
+    }
+
+    [TestCase("kitten")]
+    public void MaximumLength_Invalid(string input)
+    {
+        var result = RuleFor(input)
+            .MaximumLength(5)
+            .Result();
+
+        result.Should().BeEquivalentTo(new ValidationResult
+        {
+            IsValid = false,
+            Errors = [new() { Message = $"Value '{input}' has a length more than 5." }]
+        });
+    }
+}

CodingFlow.FluentValidation/Validators/MaximumLengthValidator.cs

@@ -0,0 +1,27 @@
+namespace CodingFlow.FluentValidation.Validators;
+
+public static class MaximumLengthValidator
+{
+    /// <summary>
+    /// Ensures the string has a length that is at most a maximum.
+    /// </summary>
+    /// <typeparam name="T">Input type.</typeparam>
+    /// <param name="validation"></param>
+    /// <param name="input">String to check length.</param>
+    /// <param name="maximum">Maximum length of the string.</param>
+    /// <returns></returns>
+    public static FluentValidation<string> MaximumLength(this FluentValidation<string> validation, int maximum)
+    {
+        Validate(validation, maximum);
+
+        return validation;
+    }
+
+    private static void Validate(FluentValidation<string> validation, int maximum)
+    {
+        validation.Validate(
+            validation => validation.Input.Length <= maximum,
+            new ValidationError($"Value '{validation.Input}' has a length more than {maximum}.")
+        );
+    }
+}

Examples/MaximumLengthExample.cs

@@ -0,0 +1,18 @@
+using CodingFlow.FluentValidation.Validators;
+using static CodingFlow.FluentValidation.Validations;
+
+namespace Examples;
+
+internal class MaximumLengthExample
+{
+    public void Run()
+    {
+        var input = "some string";
+
+        // begin-snippet: MaximumLengthExample
+        RuleFor(input)
+            .MaximumLength(5) // Must be at most 5 characters long.
+            .Result();
+        // end-snippet
+    }
+}

README.md

@@ -120,6 +120,20 @@ RuleFor(input)
 <sup><a href='/Examples/MinimumLengthExample.cs#L12-L16' title='Snippet source file'>snippet source</a> | <a href='#snippet-MinimumLengthExample' title='Start of snippet'>anchor</a></sup>
 <!-- endSnippet -->
 
+## MaximumLength Validator
+
+Ensures the string has a maximum length.
+
+<!-- snippet: MaximumLengthExample -->
+<a id='snippet-MaximumLengthExample'></a>
+```cs
+RuleFor(input)
+    .MaximumLength(5) // Must be at most 5 characters long.
+    .Result();
+```
+<sup><a href='/Examples/MinimumLengthExample - Copy.cs#L12-L16' title='Snippet source file'>snippet source</a> | <a href='#snippet-MaximumLengthExample' title='Start of snippet'>anchor</a></sup>
+<!-- endSnippet -->
+
 ## Regular Expression Validator
 
 Aka `Matches`, ensure the string passes a regular expression test.

README.source.md

@@ -53,6 +53,12 @@ Ensures the string has a minimum length.
 
 snippet: MinimumLengthExample
 
+## MaximumLength Validator
+
+Ensures the string has a maximum length.
+
+snippet: MaximumLengthExample
+
 ## Regular Expression Validator
 
 Aka `Matches`, ensure the string passes a regular expression test.