AutoLocalize

[Releases]

AutoLocalize is a Fody weaver that fills in ErrorMessageResourceType and ErrorMessageResourceName for your ValidationAttribute based annotations so you only declare your resource type once per assembly.

Problem description

It's not possible to have DataAnnotations validation attributes automatically pick up the current locale and present translated messages.

If you have translated resource files then you can set ErrorMessageResourceType and ErrorMessageResourceName on your validation attributes, but when you have thousands of them this can become troublesome and error-prone.

Solution

AutoLocalize allows you to specify ErrorMessageResourceType at project level, which will then be used on every instance of validation attributes that do not already have that property set. It will also add ErrorMessageResourceName based on a convention.

Getting started

1. Install Fody (if you do not already use it) and AutoLocalize:

   <ItemGroup>
     <PackageReference Include="Fody" Version="6.*" PrivateAssets="All" />
     <PackageReference Include="Morris.AutoLocalize.Fody" Version="1.*" />
   </ItemGroup>
   

2. Build once. Fody will create a FodyWeavers.xml file in your project if it does not exist.
3. Add AutoLocalize to FodyWeavers.xml, then build again so weaving runs.

   <Weavers xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="FodyWeavers.xsd">
     <Morris.AutoLocalize />
   </Weavers>
   

4. Specify the assembly-level attribute that tells the weaver which resource class to use. The default ErrorMessageResourceNamePrefix is "AutoLocalize_" if you do not set it.

   using Morris.AutoLocalize;
   using System.ComponentModel.DataAnnotations;
   
   [assembly: AutoLocalizeValidationAttributes(
       typeof(Resources.ValidationMessages),
       ErrorMessageResourceNamePrefix = "AutoLocalize_")]
   
   public class Person
   {
       [Required]
       [StringLength(50, MinimumLength = 2)]
       public string Name { get; set; } = string.Empty;
   }
   

Note: In case you don't know, to get a class for your resx file you need to set its Custom Tool property to PublicResXFileCodeGenerator.

What the weaver does

• Finds every field/property decorated with an attribute descended from ValidationAttribute.
• Ensures the ErrorMessageResourceType and ErrorMessageResourceName properties are set on each attribute.
• Removes the [assembly:AutoLocalizeValidationAttributes] attribute from your build output.
• Removes the assembly reference to Morris.AutoLocalize from your build output, so your runtime assembly has no extra dependencies.

ValidationAttribute update rules

• ErrorMessageResourceType is set to the value specified in the [assembly:AutoLocalizeValidationAttributes({value here})] attribute you added to your project.
• ErrorMessageResourceName is set to {Prefix}_{ShortAttributeName}
• If either the ErrorMessageResourceType or ErrorMessage properties are set on the attribute then it is assumed you want a specific error message, so AutoLocalize will leave the validation attribute untouched.

Resource automatic naming algorithm

• Prefix = AutoLocalize_ - this can be overridden when declaring your [assembly:AutoLocalizeValidationAttributes(typeof(MyResource))] attribute by setting the ErrorMessageResourceNamePrefix property.
• ShortAttributeName = The class name of the attribute that descends from ValidationAttribute without the word Attribute at the end.
  • RequiredAttribute => Required
  • SomeGenericValidationAttribute<int> => SomeGenericValidation

Examples

[assembly:AutoLocalizeValidationAttributes(typeof(DataAnnotationsMessages))]

|Attribute|ErrorMessageResourceType|ErrorMessageResourceName| |---------|------------------------|------------------------| |[Required]|DataAnnotationsMessages|AutoLocalize_Required| |[Range(0, int.MaxValue, ErrorMessageResourceName="CannotBeNegative")]|DataAnnotationsMessages|<unaltered>| |[EmailAddress(ErrorMessageResourceType=typeof(X), ErrorMessageResourceName="MustBeAValidEmailAddress")]|<unaltered>|<unaltered>| |[EmailAddress(ErrorMessage="{0} must be a valid email address")]|<unaltered>|<unaltered>|

[assembly:AutoLocalizeValidationAttributes(
   typeof(DataAnnotationsMessages),
   ErrorMessageResourceNamePrefix = "ValidationError_"
   )]

|Attribute|ErrorMessageResourceType|ErrorMessageResourceName| |---------|------------------------|------------------------| |[Required]|DataAnnotationsMessages|ValidationError_Required|

Manifest of resource keys

During weaving a CSV file named after your project (e.g. MyProject.Morris.AutoLocalize.ValidationAttributes.csv) is written next to the project file. It contains all resource keys the weaver added or discovered:

ErrorMessageResourceName
AutoLocalize_Required
AutoLocalize_StringLength

Use this manifest to ensure your resource file contains entries for each key.

Automatic translation

There is a script in the root of this repository named TranslateLanguage.ps1.

This script will use ChatGPT API to translate your resx files into another language. Instructions on how to run it are at the top of that file.