README-NuGet.md

DataAnnotationValuesExtractor

A C# source generator that automatically extracts values from data annotation attributes and exposes them as strongly-typed constants. Access your StringLength,MinLength, MaxLength, Range, Required, Display and Description attribute values as constants in your classes.

Why Use This?

When working with data annotations, you often need to reference validation constraints. A good way to solve it is to create constants. But it takes time to do and makes your data models harder to read. And it's harder when your models are auto generated like when you are scaffolding with Entity Framework.

This source generator creates the constants automatically for you. If you have this model:

public partial class Product
{
    [Required]
    [StringLength(100)]
    public string? Name { get; set; }

    [Required]
    [Range(0.01, 999999.99)]
    public decimal Price { get; set; }

    [MinLength(1)]
    [MaxLength(50)]
    public string[]? Tags { get; set; }
}

Constants will be generated that you can access like this:

// Name length constraints
int maxNameLength = Product.Annotations.Name.MaximumLength; // 100
bool nameRequired = Product.Annotations.Name.IsRequired; // true

// Price constraints
double minPrice = Product.Annotations.Price.Minimum; // 0.01
double maxPrice = Product.Annotations.Price.Maximum; // 999999.99

// Tags length constraints
int tagsMinLength = Product.Annotations.Tags.MinLength; // 1
int tagsMaxLength = Product.Annotations.Tags.MaxLength; // 50

Usage Patterns

There are two ways to configure DataAnnotationValuesExtractor depending on your needs:

1. Direct Approach

Apply [DataAnnotationValues] directly to each class you want to generate constants for:

[DataAnnotationValues(StringLength = true, MinLength = true, MaxLength = true, Range = true, Required = true, Display = true, Description = true)]
public partial class Product
{
    [Display(Name = "Product name")]
    [Description("Name of the product")]
    [Required]
    [StringLength(100)]
    public string? Name { get; set; }

    [Display(Name = "Product price")]
    [Description("Price of the product")]
    [Required]
    [Range(0.01, 999999.99)]
    public decimal Price { get; set; }

    [MinLength(1)]
    [MaxLength(50)]
    public string[]? Tags { get; set; }

    public string? Sku { get; set; }
}

2. Centralized Approach

Create a dummy class and use the DataAnnotationValuesToGenerate attribute for each class you want to generate constants for. You can use the DataAnnotationValuesConfiguration attribute to configure what to be generated.

using Pekspro.DataAnnotationValuesExtractor;

[DataAnnotationValuesConfiguration(StringLength = true, Range = true, MinLength = true, MaxLength = true, Required = true, Display = true, Description = true)]
[DataAnnotationValuesToGenerate(typeof(Customer))]
[DataAnnotationValuesToGenerate(typeof(Order))]
[DataAnnotationValuesToGenerate(typeof(Product))]
partial class ValidationConstants
{
}

Your model classes remain unchanged.

This approach is especially useful when working with auto-generated models, such as those created by Entity Framework scaffolding. If you do, and you have all your models in a folder, you can use this PowerShell script to generate the attributes for all models in that folder:

Get-ChildItem -Filter '*.cs' |
    Where-Object { -not ($_.BaseName -match '(?i)context') } |
    ForEach-Object { "[DataAnnotationValuesToGenerate(typeof($($_.BaseName)))]" } |
    Set-Clipboard

Use the generated constants

No matter which approach your are using, you can access generated constants like this:

// Name
int maxNameLength = Product.Annotations.Name.MaximumLength; // 100
int minNameLength = Product.Annotations.Name.MinimumLength; // 0
bool nameRequired = Product.Annotations.Name.IsRequired; // true
string? nameDisplayName = Product.Annotations.Name.Display.Name; // Product name
string? nameDescription = Product.Annotations.Name.Description.Text; // Name description

// Price
double minPrice = Product.Annotations.Price.Minimum; // 0.01
double maxPrice = Product.Annotations.Price.Maximum; // 999999.99
bool priceRequired = Product.Annotations.Price.IsRequired;
string? priceDisplayName = Product.Annotations.Price.Display.Name; // Price name
string? priceDescription = Product.Annotations.Price.Description.Text; // Price description

// Tags
int tagsMinLength = Product.Annotations.Tags.MinLength; // 1
int tagsMaxLength = Product.Annotations.Tags.MaxLength; // 50

// Sku
bool skuRequired = Product.Annotations.Sku.IsRequired; // false

Installation

Add the package to your project:

dotnet add package Pekspro.DataAnnotationValuesExtractor

For optimal setup, configure the package reference in your .csproj to exclude it from your output assembly:

<ItemGroup>
  <PackageReference Include="Pekspro.DataAnnotationValuesExtractor" Version="0.0.1" 
    PrivateAssets="all" ExcludeAssets="runtime" />
</ItemGroup>

Links

You can find more information and can report issues on GitHub.