BLOB Storing

It is typical to store file contents in an application and read these file contents on need. Not only files, but you may also need to save various types of large binary objects, a.k.a. BLOBs, into a storage. For example, you may want to save user profile pictures.

A BLOB is a typically byte array. There are various places to store a BLOB item; storing in the local file system, in a shared database or on the Azure BLOB storage can be options.

The ABP provides an abstraction to work with BLOBs and provides some pre-built storage providers that you can easily integrate to. Having such an abstraction has some benefits;

You can easily integrate to your favorite BLOB storage provides with a few lines of configuration.
You can then easily change your BLOB storage without changing your application code.
If you want to create reusable application modules, you don't need to make assumption about how the BLOBs are stored.

ABP BLOB Storage system is also compatible to other ABP features like multi-tenancy.

BLOB Storage Providers

The ABP has already the following storage provider implementations:

File System: Stores BLOBs in a folder of the local file system, as standard files.
Database: Stores BLOBs in a database.
Azure: Stores BLOBs on the Azure BLOB storage.
Aliyun: Stores BLOBs on the Aliyun Storage Service.
Minio: Stores BLOBs on the MinIO Object storage.
Aws: Stores BLOBs on the Amazon Simple Storage Service.

More providers will be implemented by the time. You can request it for your favorite provider or create it yourself and contribute to the ABP.

Multiple providers can be used together by the help of the container system, where each container can uses a different provider.

BLOB storing system can not work unless you configure a storage provider. Refer to the linked documents for the storage provider configurations.

Installation

Volo.Abp.BlobStoring is the main package that defines the BLOB storing services. You can use this package to use the BLOB Storing system without depending a specific storage provider.

Use the ABP CLI to add this package to your project:

Install the ABP CLI, if you haven't installed it.
Open a command line (terminal) in the directory of the .csproj file you want to add the Volo.Abp.BlobStoring package.
Run abp add-package Volo.Abp.BlobStoring command.

If you want to do it manually, install the Volo.Abp.BlobStoring NuGet package to your project and add [DependsOn(typeof(AbpBlobStoringModule))] to the ABP module class inside your project.

The IBlobContainer

IBlobContainer is the main interface to store and read BLOBs. Your application may have multiple containers and each container can be separately configured. But, there is a default container that can be simply used by injecting the IBlobContainer.

Example: Simply save and read bytes of a named BLOB

using System.Threading.Tasks;
using Volo.Abp.BlobStoring;
using Volo.Abp.DependencyInjection;

namespace AbpDemo
{
    public class MyService : ITransientDependency
    {
        private readonly IBlobContainer _blobContainer;

        public MyService(IBlobContainer blobContainer)
        {
            _blobContainer = blobContainer;
        }

        public async Task SaveBytesAsync(byte[] bytes)
        {
            await _blobContainer.SaveAsync("my-blob-1", bytes);
        }
        
        public async Task<byte[]> GetBytesAsync()
        {
            return await _blobContainer.GetAllBytesOrNullAsync("my-blob-1");
        }
    }
}

This service saves the given bytes with the my-blob-1 name and then gets the previously saved bytes with the same name.

A BLOB is a named object and each BLOB should have a unique name, which is an arbitrary string.

IBlobContainer can work with Stream and byte[] objects, which will be detailed in the next sections.

Saving BLOBs

SaveAsync method is used to save a new BLOB or replace an existing BLOB. It can save a Stream by default, but there is a shortcut extension method to save byte arrays.

SaveAsync gets the following parameters:

name (string): Unique name of the BLOB.
stream (Stream) or bytes (byte[]): The stream to read the BLOB content or a byte array.
overrideExisting (bool): Set true to replace the BLOB content if it does already exists. Default value is false and throws BlobAlreadyExistsException if there is already a BLOB in the container with the same name.

Reading/Getting BLOBs

GetAsync: Only gets a BLOB name and returns a Stream object that can be used to read the BLOB content. Always dispose the stream after using it. This method throws exception, if it can not find the BLOB with the given name.
GetOrNullAsync: In opposite to the GetAsync method, this one returns null if there is no BLOB found with the given name.
GetAllBytesAsync: Returns a byte[] instead of a Stream. Still throws exception if can not find the BLOB with the given name.
GetAllBytesOrNullAsync: In opposite to the GetAllBytesAsync method, this one returns null if there is no BLOB found with the given name.

Deleting BLOBs

DeleteAsync method gets a BLOB name and deletes the BLOB data. It doesn't throw any exception if given BLOB was not found. Instead, it returns a bool indicating that the BLOB was actually deleted or not, if you care about it.

Other Methods

ExistsAsync method simply checks if there is a BLOB in the container with the given name.

About Naming the BLOBs

There is not a rule for naming the BLOBs. A BLOB name is just a string that is unique per container (and per tenant - see the "Multi-Tenancy" section). However, different storage providers may conventionally implement some practices. For example, the File System Provider use directory separators (/) and file extensions in your BLOB name (if your BLOB name is images/common/x.png then it is saved as x.png in the images/common folder inside the root container folder).

Typed IBlobContainer

Typed BLOB container system is a way of creating and managing multiple containers in an application;

Each container is separately stored. That means the BLOB names should be unique in a container and two BLOBs with the same name can live in different containers without effecting each other.
Each container can be separately configured, so each container can use a different storage provider based on your configuration.

To create a typed container, you need to create a simple class decorated with the BlobContainerName attribute:

using Volo.Abp.BlobStoring;

namespace AbpDemo
{
    [BlobContainerName("profile-pictures")]
    public class ProfilePictureContainer
    {
        
    }
}

If you don't use the BlobContainerName attribute, ABP uses the full name of the class (with namespace), but it is always recommended to use a container name which is stable and does not change even if you rename the class.

Once you create the container class, you can inject IBlobContainer<T> for your container type.

Example: An application service to save and read profile picture of the current user

[Authorize]
public class ProfileAppService : ApplicationService
{
    private readonly IBlobContainer<ProfilePictureContainer> _blobContainer;

    public ProfileAppService(IBlobContainer<ProfilePictureContainer> blobContainer)
    {
        _blobContainer = blobContainer;
    }

    public async Task SaveProfilePictureAsync(byte[] bytes)
    {
        var blobName = CurrentUser.GetId().ToString();
        await _blobContainer.SaveAsync(blobName, bytes);
    }
    
    public async Task<byte[]> GetProfilePictureAsync()
    {
        var blobName = CurrentUser.GetId().ToString();
        return await _blobContainer.GetAllBytesOrNullAsync(blobName);
    }
}

IBlobContainer<T> has the same methods with the IBlobContainer.

It is a good practice to always use a typed container while developing re-usable modules, so the final application can configure the provider for your container without effecting the other containers.

The Default Container

If you don't use the generic argument and directly inject the IBlobContainer (as explained before), you get the default container. Another way of injecting the default container is using IBlobContainer<DefaultContainer>, which returns exactly the same container.

The name of the default container is default.

Named Containers

Typed containers are just shortcuts for named containers. You can inject and use the IBlobContainerFactory to get a BLOB container by its name:

public class ProfileAppService : ApplicationService
{
    private readonly IBlobContainer _blobContainer;

    public ProfileAppService(IBlobContainerFactory blobContainerFactory)
    {
        _blobContainer = blobContainerFactory.Create("profile-pictures");
    }

    //...
}

IBlobContainerFactory

IBlobContainerFactory is the service that is used to create the BLOB containers. One example was shown above.

Example: Create a container by name

var blobContainer = blobContainerFactory.Create("profile-pictures");

Example: Create a container by type

var blobContainer = blobContainerFactory.Create<ProfilePictureContainer>();

You generally don't need to use the IBlobContainerFactory since it is used internally, when you inject a IBlobContainer or IBlobContainer<T>.

Configuring the Containers

Containers should be configured before using them. The most fundamental configuration is to select a BLOB storage provider (see the "BLOB Storage Providers" section above).

AbpBlobStoringOptions is the options class to configure the containers. You can configure the options inside the ConfigureServices method of your module.

Configure a Single Container

Configure<AbpBlobStoringOptions>(options =>
{
    options.Containers.Configure<ProfilePictureContainer>(container =>
    {
        //TODO...
    });
});

This example configures the ProfilePictureContainer. You can also configure by the container name:

Configure<AbpBlobStoringOptions>(options =>
{
    options.Containers.Configure("profile-pictures", container =>
    {
        //TODO...
    });
});

Configure the Default Container

Configure<AbpBlobStoringOptions>(options =>
{
    options.Containers.ConfigureDefault(container =>
    {
        //TODO...
    });
});

There is a special case about the default container; If you don't specify a configuration for a container, it fallbacks to the default container configuration. This is a good way to configure defaults for all containers and specialize configuration for a specific container when needed.

Configure All Containers

Configure<AbpBlobStoringOptions>(options =>
{
    options.Containers.ConfigureAll((containerName, containerConfiguration) =>
    {
        //TODO...
    });
});

This is a way to configure all the containers.

The main difference from configuring the default container is that ConfigureAll overrides the configuration even if it was specialized for a specific container.

Multi-Tenancy

If your application is set as multi-tenant, the BLOB Storage system works seamlessly with the multi-tenancy. All the providers implement multi-tenancy as a standard feature. They isolate BLOBs of different tenants from each other, so they can only access to their own BLOBs. It means you can use the same BLOB name for different tenants.

If your application is multi-tenant, you may want to control multi-tenancy behavior of the containers individually. For example, you may want to disable multi-tenancy for a specific container, so the BLOBs inside it will be available to all the tenants. This is a way to share BLOBs among all tenants.

Example: Disable multi-tenancy for a specific container

Configure<AbpBlobStoringOptions>(options =>
{
    options.Containers.Configure<ProfilePictureContainer>(container =>
    {
        container.IsMultiTenant = false;
    });
});

If your application is not multi-tenant, no worry, it works as expected. You don't need to configure the IsMultiTenant option.

Extending the BLOB Storing System

Most of the times, you won't need to customize the BLOB storage system except creating a custom BLOB storage provider. However, you can replace any service (injected via dependency injection), if you need. Here, some other services not mentioned above, but you may want to know:

IBlobProviderSelector is used to get a IBlobProvider instance by a container name. Default implementation (DefaultBlobProviderSelector) selects the provider using the configuration.
IBlobContainerConfigurationProvider is used to get the BlobContainerConfiguration for a given container name. Default implementation (DefaultBlobContainerConfigurationProvider) gets the configuration from the AbpBlobStoringOptions explained above.

BLOB Storing vs File Management System

Notice that BLOB storing is not a file management system. It is a low level system that is used to save, get and delete named BLOBs. It doesn't provide a hierarchical structure like directories, you may expect from a typical file system.

If you want to create folders and move files between folders, assign permissions to files and share files between users then you need to implement your own application on top of the BLOB Storage system.

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