DatabaseLayer_DocumentDataAPI (DLDDAPI)

The DocumentDataAPI is the main interface to the document_data database schema, and provides endpoints to retrieve, insert, update, and delete its contents.
Besides the actual API, the project also includes a script with all table definitions for the schema, as well as a tool to easily deploy this schema in any environment.

The API is set up as an ASP.NET Core 6.0 web API, and is therefore written in C#.

Architecture

Fig.1 - Diagram of the DocumentDataAPI architecture
(as of November 2022)

The API can be divided into the following segments:

• The API Controllers define the endpoints that other applications can use to access the document_data database. For example, the SourceController exposes the endpoint GET https://localhost:8000/document-data-api/sources (assuming that the API is hosted locally on port 8000), which will return a list of all sources in the database in the JSON format. These controllers also perform most error handling, since they should be able to send appropriate responses to requests. E.g., if an error occurs while fulfilling a request, it will respond with a status 500 - Internal Server Error.
• The Repositories provide methods to actually manipulate and retrieve data from the database. The API controllers use these repositories to fulfill requests. They are implemented as interfaces to allow for switching database providers as well as increased testability.
• The Database segment includes the various models of the database tables (i.e. the SourceModel, which is a model of the sources table). It also includes deployment scripts that the DatabaseDeployHelper uses to actually deploy the database schema with all tables to a database.
• The Options are used throughout the entire application, and simply provide the application settings. The setup is very typical for an ASP.NET Core application (see this tutorial): In production mode, appsettings.json is used, and in development mode, appsettings.Development.json is used. However, for settings local to your machine, use appsettings.local.json which is not added to version control. This file will automatically be prioritized over the settings in the other files.

Dependency Injection

The project is set up with Dependency Injection, which means that services should not be instantiated manually, but can instead be injected into a component through its constructor. As an example, consider the following snippet from the WordRatioController, which relies on the IWordRatioRepository to get data:

public class WordRatioController : ControllerBase
{
    private readonly IWordRatioRepository _repository;
    private readonly ILogger<WordRatioController> _logger;

    public WordRatioController(IWordRatioRepository repository, ILogger<WordRatioController> logger)
    {
        _repository = repository;
        _logger = logger;
    }
    ...
}

Fig. 2 - An example of dependency injection in the WordRatioController
(DocumentDataAPI/Controllers/WordRatioController.cs)

Notice that the IWordRatioRepository is not instantiated, but instead injected through the constructor. When the controllers are automatically set up in Program.cs, these dependencies will also automatically be set up by the dependency injection system provided in ASP.NET Core. When a dependency is used such as the IWordRatioRepository above, it must simply be registered as a service when building the application in DocumentDataAPI/Program.cs, as shown below:

...
builder.Services
    .AddSingleton<DatabaseDeployHelper>()
    .AddSingleton<ISqlHelper, DapperSqlHelper>()
    .AddSingleton<IRelevanceFunction, CosineSimilarityCalculator>()
    .AddSingleton<IDbConnectionFactory>(_ => new NpgDbConnectionFactory(databaseOptions.ConnectionString))
    .AddScoped<IDocumentContentRepository, NpgDocumentContentRepository>()
    .AddScoped<IDocumentRepository, NpgDocumentRepository>()
    .AddScoped<ISourceRepository, NpgSourceRepository>()
    .AddScoped<IWordRatioRepository, NpgWordRatioRepository>()
    ...
...

Fig. 3 - Setting up services for dependency injection
(DocumentDataAPI/Program.cs)

In line 10, the IWordRatioRepository is registered as a scoped service, and its implementation is the NpgWordRatioRepository. So in this case, this is the actual class that will be automatically injected into the WordRatioController. If we want to change this implementation to another class at a later point, we can simply replace it in this line without breaking anything in the components that use this dependency.

Contact

Wiki: https://wiki.knox.cs.aau.dk/en/Database/DocumentDataAPI/Introduction
Project Link: https://github.com/Knox-AAU/DatabaseLayer_DocumentDataAPI/

Authors

2022

Kasper Kaputu Henningsen ([email protected])
Mikkel Raakjær Stidsen ([email protected])
Nicolai Hejlesen Jørgensen ([email protected])
Nikolaj Dam ([email protected])
Sarmilan Tharmabalan ([email protected])
Tobias Lausten ([email protected])