public class MyEntity : ICosmosEntity
{
    public string Id { get; set; }
    public string Title { get; set; }
    public string Description { get; set; }
}

/*
 Name of the cosmos database, optional.
 If not provided, name of class will be used (MyDatabase in this case).
*/
[DatabaseId("FooDatabase")]
public class MyDatabase : CosmosDatabase
{
    public MyDatabase(DatabaseOptions<MyDatabase> options)
        : base(options)
    { }

    /*
    Name of the cosmos collection, optional.
    If not provided, name of class will be used (MyEntities in this case).
    */
    [CollectionId("FooCollection")]
    public ICosmosDbCollection<MyEntity> MyEntities { get; private set; }
}

public class MyEntity : ICosmosEntity
{
    public string Id { get; set; }
    public string Title { get; set; }
    public string Description { get; set; }
}

public class MyDatabase : CosmosDatabase
{
    public MyDatabase(DatabaseOptions<MyDatabase> options)
        : base(options, initialize: false)
    { }

    public ICosmosDbCollection<MyEntity> MyEntities { get; private set; }

    protected override void OnModelCreating(DatabaseModelBuilder<MyDatabase> modelBuilder)
    {
        modelBuilder.DatabaseId("FooDatabase");

        modelBuilder.Collection(x => x.MyEntities)
            .CollectionId("FooCollection");
    }
}

var myConnectionString = configuration.GetConnectionString("CosmosDb");

services
    ...
    // This will register the database type and all it's collections
    .AddCosmosDatabase<MyDatabase>(options => options.UseConnectionString(myConnectionString))
    ...
    ;

public class MyController : ControllerBase
{
    private readonly ICosmosDbCollection<MyEntity> _collection;

    public MyController(ICosmosDbCollection<MyEntity> collection)
    {
        _collection = collection;
    }

    [HttpGet]
    public Task<SearchResponse<MyEntity>> List(string query)
    {
        var searchRequest = new SearchRequest<MyEntity>
        {
            Query = query
        };
        return _collection.SearchAsync(searchRequest);
    }

    [HttpGet("{id}")]
    public Task<MyEntity> Get(string id)
    {
        return _collection.GetAsync(id);
    }

    [HttpPost]
    public Task Upsert(MyEntity input)
    {
        return _collection.UpsertAsync(input);
    }
}