Using MarcelloDB starts with the creation of a session.

The session manages access to the filesystem as well as transactions and concurrency. Interaction with MarcelloDB always requires a valid session.

MarcelloDB is a portable class library, but requires injection of implementations of platform specific features. (Currently, MarcelloDB only relies on a platform specific implementation for reading and writing files.) These platform specifics are implemented in Platform

The Platform implementation for mono/.net (for Xamarin iOS and Android, and regular mono/.net) can be found in the Marcello.netfx assembly.

The implementation for Windows Phone 8.1 and Windows 8.1/10 Apps can be found in the Marcello.uwp assembly.

Creating a session requires a platform

Create the platform object

var platform =  new Platform();

Then create the session using the platform and a path to a folder. MarcelloDB will read and write it's data to and from this folder.

(You can do this in a portable class library)

var session = new MarcelloDB.Session(platform, "/path/to/data/folder/");

Sessions should be property disposed, failing to do so will keep your data files locked untill your process exits.

//Once you are done with the session, dispose it.

The session will remain valid until it is garbage collected or disposed. A good approach would be to keep it around for a long time. Attach it to your App instance, keep it in a static or singleton or inside a IOC Container.


MarcelloDB organizes it's data in collection-files and collections. A session manages one or more collection-files. A collection-file contains one or more collections.

A collection-file maps directly to a file in the sessions folder.

This file contains the data and indexes of all collections in that collection-file.

If it makes sense in your use-case - a product catalog for instance - you could generate a collection-file on the server and download it from your clients.

You access a collection-file by it's actual filename.

// is the actual file name within the sessions folder
var productsFile = session[""];


A collection is a bit like a table in a SQL Database.

It manages objects of a specific type, including subclasses.

Deep down inside, MarcelloDB is a key-value store. It saves objects and allows you to retreive them back (or update/delete) by their ID. Since this ID is so important, it has been made part of the construction of a collection.

A collection is a generic type with at least 2 generic type parameters. The first one is the type of the objects you want to store, the second one is the type of your object's ID value.

The third generic parameter is the index definition. Read about indexes

When constructing the collection, you need to give it a name - like you give tables a name - and you have to provide a function to retrieve the ID from an object.

like this:

//             Store instances of  [Book]  [with string ID]    [get ID from book]
//                                   ||      ||                       ||
var books = productsFile.Collection<Book, string>("books", book => book.BookId);

//             Store instances of  [Dvd] [with Guid ID] [get ID from dvd]
//                                  ||    ||                  ||
var dvds = productsFile.Collection<Dvd, Guid>("dvd", dvd =>;

If you use different collection-names you can have multiple collections for the same type within one collection-file.

var dvdCollection = productsFile.Collection<Dvd, Guid>("dvds", dvd =>;
var newDvdCollection = productsFile.Collection<Dvd, Guid>("new-dvds", dvd =>;