PropertyResolvers 0.0.9

PropertyResolvers

A C# source generator that creates type-safe property resolver classes. Instead of using reflection at runtime to extract property values from objects, PropertyResolvers generates compile-time switch expressions that efficiently resolve property values across multiple types.

Installation

dotnet add package PropertyResolvers

Quick Start

1. Add assembly-level attributes to specify which properties you want resolvers for:

using PropertyResolvers.Attributes;

[assembly: GeneratePropertyResolver("AccountId")]
[assembly: GeneratePropertyResolver("TenantId")]

2. The generator automatically finds all types with matching properties and generates resolver classes:

// Generated code (AccountIdResolver.g.cs)
public static class AccountIdResolver
{
    public static string? GetAccountId(object? obj) => obj switch
    {
        global::MyApp.Order x => x.AccountId.ToString(),
        global::MyApp.Customer x => x.AccountId.ToString(),
        global::MyApp.Invoice x => x.AccountId.ToString(),
        _ => null
    };
}

3. Use the generated resolvers in your code:

var order = new Order { AccountId = "ACC-123" };
var customer = new Customer { AccountId = "ACC-456" };
var product = new Product { Name = "Widget" }; // No AccountId property

var id1 = AccountIdResolver.GetAccountId(order);    // "ACC-123"
var id2 = AccountIdResolver.GetAccountId(customer); // "ACC-456"
var id3 = AccountIdResolver.GetAccountId(product);  // null

Use Cases

• Multi-tenant applications: Extract TenantId from any entity without reflection
• Audit logging: Consistently retrieve identifier properties across different entity types
• Event sourcing: Extract aggregate IDs from various event types
• API responses: Normalize property access across different DTO types

Configuration Options

Basic Usage

[assembly: GeneratePropertyResolver("AccountId")]

Namespace Filtering

Include only specific namespaces:

[assembly: GeneratePropertyResolver("AccountId", IncludeNamespaces = new[] { "MyApp.Domain", "MyApp.Entities" })]

Exclude specific namespaces:

[assembly: GeneratePropertyResolver("AccountId", ExcludeNamespaces = new[] { "System", "Microsoft" })]

Multiple Resolvers

You can generate resolvers for multiple properties:

[assembly: GeneratePropertyResolver("AccountId", ExcludeNamespaces = new[] { "System", "Microsoft" })]
[assembly: GeneratePropertyResolver("TenantId", ExcludeNamespaces = new[] { "System", "Microsoft" })]
[assembly: GeneratePropertyResolver("EntityId", ExcludeNamespaces = new[] { "System", "Microsoft" })]

Attribute Reference

GeneratePropertyResolverAttribute

Analyzer

The package includes an analyzer that detects duplicate property resolver definitions:

// PR001: Property resolver for 'AccountId' is already defined
[assembly: GeneratePropertyResolver("AccountId")]
[assembly: GeneratePropertyResolver("AccountId")]  // Error: duplicate

Duplicate detection is case-insensitive, so "AccountId" and "accountid" are considered duplicates.

How It Works

1. The generator scans all assembly-level GeneratePropertyResolver attributes
2. For each attribute, it finds all classes and structs with a matching property name
3. It generates a static resolver class with a switch expression that pattern-matches on the object type
4. The generated code uses global:: prefixes to avoid namespace conflicts

Generated Code Location

The generated resolver classes are placed in a namespace matching your assembly name. For example, if your assembly is MyApp, the resolvers will be in the MyApp namespace.

Requirements

• .NET Standard 2.0 compatible (works with .NET Framework 4.7.2+ and .NET Core 2.0+)
• C# 9.0 or later (for switch expressions in generated code)
• Visual Studio 2022 17.0+ or compatible IDE with Roslyn 4.0+ support

License

MIT