Automatic Discovery and Registration

The Manual Registration of Request Handlers Problem

Manual registration of request handlers with dependency injection mechanism is acceptable for relatively small projects but becomes tedious in large systems where new operations are added frequently:

services.AddKeyedTransient<IRpcRequestHandler, BankMakeDepositHandler>("Bank.MakeDeposit");
services.AddKeyedScoped<IRpcRequestHandler, ShipmentSearchHandler>("Shipment.Search");
...

The Scalable Approach

A more scalable approach is to register handlers automatically based on assembly attributes and request handler attributes.

For example, we may define an attribute named RpcAssembly, that we can put on assemblies that contain RPC handlers:

[AttributeUsage(AttributeTargets.Assembly, AllowMultiple = false)]
public sealed class RpcAssemblyAttribute : Attribute

If we have a Bank assembly that contains handlers for banking operations, we can mark it with this attribute, by writing the following line of code inside the assembly metadata file (commonly AssemblyInfo.cs):

[assembly: RpcAssembly("Bank")]

We may also define another attribute named RpcMethod, that we can put on handler classes:

[AttributeUsage(AttributeTargets.Class, AllowMultiple = false, Inherited = false)]
public sealed class RpcMethodAttribute : Attribute

If we have a handler class for the Bank.MakeDeposit operation, we can mark it with this attribute and specify the method name and description:

[RpcMethod("Bank.MakeDeposit", Description="Deposits money into an existing bank account and returns the new balance.", IsReadOnly=false)]
public class BankMakeDepositHandler

As a result, at startup, our code can:

• scan assemblies and load only those which are decorated with RpcAssembly attribute
• find classes decorated with RpcMethod attribute, read method name and description from the attribute
• register the class as a handler for that method name in dependency injection

 

Table of Content Operation-Oriented APIs and AI Tools Previous: One Operation, One Handler Next: Swagger and RPC Discoverability

 

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Business Process Programming in .Net
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