OfX

public string XId { get; set; } 
[XOf(nameof(XId))] public string X { get; set; } 

OfX is an open-source, which focus on Attribute-based data mapping, streamlines data handling across services, reduces boilerplate code, and improves maintainability

Warning

All OfX* packages need to have the same version.

Demo Project!

Project Highlights

Attribute-based Data Mapping in OfX is a feature that lets developers annotate properties in their data models with custom attributes. These attributes define how and from where data should be fetched, eliminating repetitive code and automating data retrieval. For example, imagine a scenario where Service A needs a user’s name stored in Service B. With Attribute-based Data Mapping, Service A can define a UserName property annotated with [UserOf(nameof(UserId))]. This tells the system to automatically retrieve the UserName based on UserId, without writing custom code each time.

Example:

// Basic Config
builder.Services.AddOfX(cfg =>
{
    cfg.AddAttributesContainNamespaces(typeof(UserOfAttribute).Namespace!);
    cfg.AddModelConfigurationsFromNamespaceContaining<SomeModelAssemblyMarker>();
});

// Define a custom OfXAttribute
public sealed class UserOfAttribute(string propertyName) : OfXAttribute(propertyName);

// Tell OfX which model the attribute applies to
[OfXConfigFor<UserOfAttribute>(nameof(Id), nameof(Name))]
public sealed class User
{
    public string Id { get; set; } 
    public string Name { get; set; } 
    public string Email { get; set; } 
    // Add other properties as needed
}

// Sample DTO
public sealed class SomeDataResponse
{
    public string Id { get; set; } 
    public string UserId { get; set; } 
    
    [UserOf(nameof(UserId), Expression = "Email")]
    public string UserEmail { get; set; } 

    [UserOf(nameof(UserId))]
    public string UserName { get; set; } 

    // Add other properties as needed
}

// You are touching the OfX!

The [UserOf] annotation acts as a directive to automatically retrieve UserName based on UserId,you can also fetch custom fields as Email on the User Table using Expression like [UserOf(nameof(UserId), Expression="Email")]. This eliminates the need for manual mapping logic, freeing developers to focus on core functionality rather than data plumbing.

Start with OfX

To install the OfX package, use the following NuGet command:

dotnet add package OfX

Or via the NuGet Package Manager:

Install-Package OfX

How to Use

1. Register OfX in the Dependency Injection Container

Add the OfX to your service configuration to register OfX:

builder.Services.AddOfX(cfg =>
{
    cfg.AddAttributesContainNamespaces(typeof(WhereTheAttributeDefined).Assembly);
    cfg.AddHandlersFromNamespaceContaining<SomeHandlerAssemblyMarker>(); //<- Add this one when you want to self-handle the request as the example at the end of this guide. Otherwise, if you install the package OfX-gRPC or OfX-Nats...(like OfX transport extension package), there is no need to add this one anymore!
    cfg.AddReceivedPipelines(c => c.OfType(typeof(GenericReceivedPipeline<>).OfType<OtherReceivedPipeline>());
    cfg.AddSendPipelines(c => c.OfType(typeof(GenericSendPipeline<>).OfType(typeof(OtherSendPipeline<>)));    
    // When you have the stronglyTypeId, you have to create the config how to resolve the Id(from string type) to StronglyTypeId
    cfg.AddStronglyTypeIdConverter(a => a.OfType<StronglyTypeIdRegisters>());
    cfg.AddModelConfigurationsFromNamespaceContaining<SomeModelAssemblyMarker>();
    cfg.ThrowIfException(); // Add this when you want to handle the error and know why the errors are occupied
    cfg.SetMaxObjectSpawnTimes(16); // Add this when you want to limit the maxObject spawn times. It mean you can be noticed that your objects are so complex...
});

Function Descriptions

AddAttributesContainNamespaces

cfg.AddAttributesContainNamespaces(typeof(WhereTheAttributeDefined).Assembly);

Registers assemblies that contain the attributes, used by OfX for data mapping.

The Attribute must be inherited from OfXAttribute and they will be scanned by OfX!

Parameters: Assembly: The assembly containing the (OfX) attributes.

AddHandlersFromNamespaceContaining

cfg.AddHandlersFromNamespaceContaining<SomeHandlerAssemblyMarker>(); //<- Add this one when you want to self-handle the request as the example at the end of this guide. Otherwise, if you install the package OfX-gRPC or OfX-Nats...(like OfX transport extension package), there is no need to add this one anymore!

Add assemblies that contain handlers responsible for processing queries or commands for data retrieval.

Handlers are the execution units that resolve attributes applied to models.

If this function is not invoked. The default value ItemsResponse<OfXDataResponse> is returned!

Parameters: Type: A marker type within the assembly that includes the handler implementations. Example:

cfg.AddHandlersFromNamespaceContaining<SomeHandlerAssemblyMarker>();

Here, AddHandlersFromNamespaceContaining is a type within the assembly where your handler logic resides.

AddReceivedPipelines

cfg.AddReceivedPipelines(c => c.OfType(typeof(GenericReceivedPipeline<>).OfType<OtherReceivedPipeline>());

When you want to create pipelines to handle the received request for OfXAttribute. You should use it on the server, where you fetching and response to client!

Parameters: Action<ReceivedPipeline>: add the pipelines.

Example:

cfg.AddSendPipelines(c => c.OfType(typeof(GenericSendPipeline<>).OfType(typeof(OtherSendPipeline<>)));    

AddSendPipelines

cfg.AddSendPipelines(c => c.OfType(typeof(GenericSendPipeline<>).OfType(typeof(OtherSendPipeline<>)));    

When you want to create pipelines to handle the send request for OfXAttribute. You should use it on the client, where you send request to get data!

Parameters: Action<SendPipeline>: add the pipelines.

Example:

cfg.AddReceivedPipelines(c => c.OfType(typeof(GenericPipeline<>)).OfType<OtherPipeline>());

AddStronglyTypeIdConverter

// When you have the stronglyTypeId, you have to create the config how to resolve the Id(from string type) to StronglyTypeId
cfg.AddStronglyTypeIdConverter(a => a.OfType<StronglyTypeIdRegisters>());

When your models(entities) are using Strongly Type Id, you have to configure to tell how OfX can convert from general ID type(string) to your strongly type ID.

Parameters: Action<StronglyTypeIdRegister> the strongly type ID register delegate.

OfType

You have to create a class and implement interface IStronglyTypeConverter<T>, then you have to override 2 methods( Convert and CanConvert) to help OfX convert from general Id type(string) to your strongly type. Please check the example above!

AddModelConfigurationsFromNamespaceContaining

cfg.AddModelConfigurationsFromNamespaceContaining<SomeModelAssemblyMarker>();

Locate your models and OfX will dynamic create the handler relevant to Model and OfXAttribute

ThrowIfException

cfg.ThrowIfException(); // Add this when you want to handle the error and know why the errors are occupied

This function enables strict error handling within OfX. When added, it ensures that any exceptions encountered during data mapping, request handling, or pipeline execution are not silently ignored but instead explicitly thrown. This helps developers quickly identify and debug issues by surfacing errors, making it easier to track down problems in the OfX processing flow.

SetMaxObjectSpawnTimes

cfg.SetMaxObjectSpawnTimes(16); // Add this when you want to limit the maxObject spawn times. It mean you can be noticed that your objects are so complex...

This function sets an upper limit on the number of times an object can be spawned during recursive data mapping. By default (Max spawn times: 32), OfX allows objects to be dynamically created and mapped, but in complex object structures, excessive recursive mapping can lead to performance issues or infinite loops. Setting maxTimes helps prevent excessive nesting by defining a safe threshold, ensuring that the mapping process remains efficient and controlled.

2. Integrate the OfXAttribute into Your Models, Entities, or DTOs

Apply the attribute to your properties like this:

public sealed class SomeDataResponse
{
    public string Id { get; set; }
    public string UserId { get; set; }

    [UserOf(nameof(UserId), Expression = "Email")]
    public string UserEmail { get; set; }

    [UserOf(nameof(UserId))]
    public string UserName { get; set; }

    [UserOf(nameof(UserId), Expression = "ProvinceId")]
    public string ProvinceId { get; set; }
    
    [ProvinceOf(nameof(ProvinceId), Order = 1)]
    public string ProvinceName { get; set; }
    
    [ProvinceOf(nameof(ProvinceId), Expression = "Country.Name", Order = 1)]
    public string CountryName { get; set; }

    [ProvinceOf(nameof(ProvinceId), Expression = "CountryId", Order = 1)]
    public string CountryId { get; set; }

    [CountryOf(nameof(CountryId), Expression = "Provinces[0 asc Name].Name", Order = 2)]
    public string Province { get; set; }
    
    // Add other properties as needed
}

3. Annotate OfXConfigForAttribute your models with OfXAttribute to then

OfX will dynamic create relevant proxy handler for model and OfXAttribute

Example:

[OfXConfigFor<UserOfAttribute>(nameof(Id), nameof(Name))]
public class User
{
    public string Id { get; set; }
    public string Name { get; set; }
    public string Email { get; set; }
    public string ProvinceId {get; set;}
}

4. Write the Handlers in Your Service to Fetch the Data(when you are using OfX only).

Note: If you use OfX-gRPC, OfX-Nats, OfX-RabbitMq... or other transport data layer(next version extension packages), there are no need to create Handlers anymore, they should be dynamic proxy handlers!

Implement a handler to process data requests.

Example:

public class UserRequestHandler(): IMappableRequestHandler<UserOfAttribute>
{
    public async Task<ItemsResponse<OfXDataResponse>> RequestAsync(RequestContext<UserOfAttribute> request)
    {
        // Implement data fetching logic here (e.g., via REST, RPC, or gRPC)
    }
}

5. Unlock the Full Power of Expressions 🚀

Expressions in OfX enable you to fetch external data dynamically and powerfully. By leveraging these, you can go beyond default data fetching and define specific rules to access external resources effortlessly. Let’s dive into how * Expressions* work and what makes them so versatile.

Default Data vs. External Data

• Default Data: Automatically fetched using OfX Attribute. No Expression is required.
• External Data: Define an Expression to fetch specific or relational data from other tables.

Here’s how you can harness the power of Expressions in different scenarios:

Fetching Data on the Same Table

Simple case: fetching additional fields from the same table.

public sealed class SomeDataResponse
{
    public string Id { get; set; }
    public string UserId { get; set; }

    [UserOf(nameof(UserId), Expression = "Email")]
    public string UserEmail { get; set; }

    [UserOf(nameof(UserId))]
    public string UserName { get; set; }
}

User structure:

[OfXConfigFor<UserOfAttribute>(nameof(Id), nameof(Name))]
public sealed class User
{
    public string Id { get; set; }
    public string Name { get; set; }
    public string Email { get; set; }
    ...
}

Generated SQL:

 SELECT u."Id", u.Name, u."Email"
 FROM "Users" AS u
 WHERE u."Id" IN (@__SomeUserIds__)

Fetching Data from Navigated Tables

Expressions also support navigation through navigated tables.

public sealed class SomeDataResponse
{
    ...
    [UserOf(nameof(UserId), Expression = "ProvinceId")]
    public string ProvinceId { get; set; }
    
    [ProvinceOf(nameof(ProvinceId), Expression = "Country.Name", Order = 1)]
    public string CountryName { get; set; }
    ...
}    

In this case, Expression = "Country.Name" means:

• Start from the Provinces table.

• Navigate to the Country property.

• Fetch the Name field from the Countries table.

Structures:

[OfXConfigFor<ProvinceOfAttribute>(nameof(Id), nameof(Name))]
public sealed class Province
{
    public ProvinceId Id { get; set; }
    public string Name { get; set; }
    public CountryId CountryId { get; set; }
    public Country Country { get; set; }
}

[OfXConfigFor<CountryOfAttribute>(nameof(Id), nameof(Name))]
public class Country
{
    public CountryId Id { get; set; }
    public string Name { get; set; }
    public List<Province> Provinces { get; set; }
}

If the Countries table have the single navigator(like Country on the table Provinces) to other table, you can extend the Expression to thousand kilometers :D. Like this one: Expression = "Country.[SingleNavigator]...[Universal].

Generated SQL:

SELECT p."Id", c."Name"
FROM "Provinces" AS p
         LEFT JOIN "Countries" AS c ON p."CountryId" = c."Id"
WHERE p."Id" IN (@__SomeProvinceIds___)

Mapping Objects Dynamically.

public sealed class SomeDataResponse
{
    ...
    [UserOf(nameof(UserId), Expression = "ProvinceId")]
    public string ProvinceId { get; set; }
    
    [ProvinceOf(nameof(ProvinceId), Expression = "Country", Order = 1)]
    public CountryDTO Country { get; set; }
    ...
}    

public sealed class CountryDTO
{
    public string Id { get; set; }
    public string Name {get; set;}
}

Note: The DTO structure (e.g., CountryDTO) must match the source model's structure.

• Only properties directly on the source model (e.g., Id, Name) are selected.
• Navigators (e.g., Provinces) are ignored.

Note: When you map an object, the correlation DTO should have the same structure with Model like the CountryDTO above.

Array Mapping:

Unlock powerful features for mapping collections!

1. All Items: [asc|desc Property]

• Retrieves all items ordered by the specified property.
• Example:

[CountryOf(nameof(CountryId), Expression = "Provinces[asc Name]")]
public List<ProvinceDTO> Provinces { get; set; }

Note: We will retrieve all the items of a collection on navigator property, like the Provinces on the Countries table.

2.Single Item: [0|-1 asc|desc Property]example above:

• Fetches the first (0) or last (-1) item in the collection.
• Example:

public sealed class SomeDataResponse
{
    ...
    [ProvinceOf(nameof(ProvinceId), Expression = "CountryId", Order = 1)]
    public string CountryId { get; set; }

    [CountryOf(nameof(CountryId), Expression = "Provinces[0 asc Name]", Order = 2)]
    public ProvinceDTO Province { get; set; }
    ...
}

When you select one item, you can navigate to the next level of the Table. Like this one:

public sealed class SomeDataResponse
{
    ...
    [ProvinceOf(nameof(ProvinceId), Expression = "CountryId", Order = 1)]
    public string CountryId { get; set; }

    [CountryOf(nameof(CountryId), Expression = "Provinces[0 asc Name].Name", Order = 2)]
    public string ProvinceName { get; set; }
    ...
}

3.Offset & Limit: [Offset Limit asc|desc Property]

• Retrieves a slice of the collection.
• Example:

public sealed class SomeDataResponse
{
    ...
    [ProvinceOf(nameof(ProvinceId), Expression = "CountryId", Order = 1)]
    public string CountryId { get; set; }

    [CountryOf(nameof(CountryId), Expression = "Provinces[2 10 asc Name]", Order = 2)]
    public List<ProvinceDTO> Provinces { get; set; }
    ...
}

6. OfX Attribute Order

On the chapter 5. Unlock the Full Power of Expressions we have dive into the Expression power. On this one, we will explore the Order on the OfX Attribute. Look at the first example model:

public sealed class SomeDataResponse
{
    public string Id { get; set; }
    public string UserId { get; set; }

    [UserOf(nameof(UserId), Expression = "Email")]
    public string UserEmail { get; set; }

    [UserOf(nameof(UserId))]
    public string UserName { get; set; }

    [UserOf(nameof(UserId), Expression = "ProvinceId")]
    public string ProvinceId { get; set; }
    
    [ProvinceOf(nameof(ProvinceId), Order = 1)]
    public string ProvinceName { get; set; }
    
    [ProvinceOf(nameof(ProvinceId), Expression = "Country.Name", Order = 1)]
    public string CountryName { get; set; }

    [ProvinceOf(nameof(ProvinceId), Expression = "CountryId", Order = 1)]
    public string CountryId { get; set; }

    [CountryOf(nameof(CountryId), Expression = "Provinces[0 asc Name].Name", Order = 2)]
    public string Province { get; set; }
    
    // Add other properties as needed
}

You can define Order data using OfX Attributes such as [ProvinceOf(nameof(ProvinceId), Expression = "Country.Name", Order = 1)] or [CountryOf(nameof(CountryId), Expression = "Provinces[0 asc Name].Name", Order = 2)].

By default, the Order value is 0, which means that properties marked with OfX Attributes will be fetched and set first. Afterward, properties will be fetched and set according to their defined Order values in ascending order.

You can also specify negative Order values like Order = -1 or Order = -2... In such cases, properties with negative Order values will still follow the same ordering rules and be processed accordingly.

When mapping data, imagine that you need Property A to be resolved first. If the required data is available, it will then be used as input to resolve the next set of Properties, ensuring an organized and logical flow.

Conclusion:

The Expression feature in OfX opens up endless possibilities for querying and mapping data across complex relationships. Whether you're working with single properties, nested objects, or collections, OfX has you covered. Stay tuned for even more exciting updates as we expand the capabilities of Expressions!

That all, Enjoy your moment!

Package Name	Description	.NET Version	Document
Core
OfX	OfX core	8.0, 9.0	This Document
Data Providers
OfX-EFCore	This is the OfX extension package using EntityFramework to fetch data	8.0, 9.0	ReadMe
OfX-MongoDb	This is the OfX extension package using MongoDb to fetch data	8.0, 9.0	ReadMe
Integrations
OfX-HotChocolate	OfX.HotChocolate is an integration package with HotChocolate for OfX.	8.0, 9.0	ReadMe
Transports
OfX-gRPC	OfX.gRPC is an extension package for OfX that leverages gRPC for efficient data transportation.	8.0, 9.0	ReadMe
OfX-Kafka	OfX-Kafka is an extension package for OfX that leverages Kafka for efficient data transportation.	8.0, 9.0	ReadMe
OfX-Nats	OfX-Nats is an extension package for OfX that leverages Nats for efficient data transportation.	8.0, 9.0	ReadMe
OfX-RabbitMq	OfX-RabbitMq is an extension package for OfX that leverages RabbitMq for efficient data transportation.	8.0, 9.0	ReadMe

---