The code snippets of this gist are part of https://blog.georgekosmidis.net/2019/11/02/using-litedb-in-an-asp-net-core-api/

appsettings

"LiteDbOptions": {
  "DatabaseLocation": "LiteDb/LiteDbTest.db"
}

dotnet_new

dotnet new webapi
dotnet add package LiteDB
dotnet build

LiteDbContext.cs

public class LiteDbContext : ILiteDbContext
{
    public LiteDatabase Database { get; }

    public LiteDbContext(IOptions<LiteDbOptions> options)
    {
        Database = new LiteDatabase(options.Value.DatabaseLocation);
    }
}

LiteDbWeatherForecastService.cs

public class LiteDbWeatherForecastService : ILiteDbWeatherForecastService
{
    private LiteDatabase _liteDb;

    public LiteDbWeatherForecastService(ILiteDbContext liteDbContext)
    {
        _liteDb = liteDbContext.Database;
    }

    public IEnumerable<WeatherForecast> FindAll()
    {
        return _liteDb.GetCollection<WeatherForecast>("WeatherForecast")
            .FindAll();
    }

    public WeatherForecast FindOne(int id)
    {
        return _liteDb.GetCollection<WeatherForecast>("WeatherForecast")
            .Find(x => x.Id == id).FirstOrDefault();
    }

    public bool Insert(WeatherForecast forecast)
    {
        return _liteDb.GetCollection<WeatherForecast>("Api")
            .Insert(forecast);
    }

    public bool Update(WeatherForecast forecast)
    {
        return _liteDb.GetCollection<WeatherForecast>("Api")
            .Update(forecast);
    }

    public int Delete(int id)
    {
        return _liteDb.GetCollection<WeatherForecast>("Api")
            .Delete(x => x.Id == id);
    }
}

services_ILiteDbContext.cs

services.AddSingleton<ILiteDbContext, LiteDbContext>();

services_ILiteDbWeatherForecastService.cs

services.AddTransient<ILiteDbWeatherForecastService, LiteDbWeatherForecastService>();

WeatherForecast.cs

public class WeatherForecast
{
    public int Id { get; set; }//New addition, Id wasn't there 
    public DateTime Date { get; set; }
    public int TemperatureC { get; set; }
    public int TemperatureF => 32 + (int)(TemperatureC / 0.5556);
    public string Summary { get; set; }
}

WeatherForecastController.cs

[ApiController]
[Route("[controller]")]
public class WeatherForecastController : ControllerBase
{
    private readonly ILogger<WeatherForecastController> _logger;
    private readonly ILiteDbWeatherForecastService _forecastDbService;

    public WeatherForecastController(ILogger<WeatherForecastController> logger, ILiteDbWeatherForecastService forecastDbService)
    {
        _forecastDbService = forecastDbService;
        _logger = logger;
    }

    [HttpGet]
    public IEnumerable<WeatherForecast> Get()
    {
        return _forecastDbService.FindAll();
    }

    [HttpGet("{id}", Name = "FindOne")]
    public ActionResult<WeatherForecast> Get(int id)
    {
        var result = _forecastDbService.FindOne(id);
        if (result != default)
            return Ok(_forecastDbService.FindOne(id));
        else
            return NotFound();
    }

    [HttpPost]
    public ActionResult<WeatherForecast> Insert(WeatherForecast dto)
    {
        var id = _forecastDbService.Insert(dto);
        if (id != default)
            return CreatedAtAction("FindOne", _forecastDbService.FindOne(id));
        else
            return BadRequest();
    }

    [HttpPut]
    public ActionResult<WeatherForecast> Update(WeatherForecast dto)
    {
        var result = _forecastDbService.Update(dto);
        if (result)
            return NoContent();
        else
            return NotFound();
    }

    [HttpDelete("{id}")]
    public ActionResult<WeatherForecast> Delete(int id)
    {
        var result = _forecastDbService.Delete(id);
        if (result > 0)
            return NoContent();
        else
            return NotFound();
    }
}