This sample was created to solve a very specific problem - a problem which may not exist by the time you read this.
Following a domain driven design approach (DDD) suggests that collection properties inside domain entities should be readonly. In fact, to update the contents of a collection specific methods to do just that have to be created, e.g. AddEItem, RemoveItem and so on. This leaves the entity in full control of the collection, as it should be.
When using Entity Framework Core (EF Core) for a relational database this works just fine. But when using EF Core for a document database (CosmosDb) the entity is serialized and deserialized using System.Text.Json on its way to and from the store.
And as it turns out, System.Text.Json will not populate a readonly collection unless it finds a constructor that uses public or init setters. And that breaks the encapsulation we set up for the collection inside the entity. No bueno.
Since this is primarily an infrastructure issue DDD experts (@ardalis) suggest introducing a mapping functionality in that layer, thereby insulating the core domain project from any knowledge about storage concerns. With a bit of additional work it's even possible to insulate the API layer from knowing about storage issues as well.
A series of interfaces and generic repositories can be created to effectively manage this.
This example presupposes that an implementation of a document repository would already exist.
To use this approach the following additional classes would need to be created:
- A document representation of the domain entity that can work with CosmosDb correctly, e.g.
InvitationDocument - A strongly typed implementation of IMapper<T,D> that will handle the proper mapping back and forth, e.g.
IMapper<Invitation,InvitationDocument - A marker interface that implements the generic IMappingRepository<T,D> (a one liner), e.g.
IInvitationRepository - A class that inherits from
GenericMappingRepositoryBaseand implements the marker interface above (basically just a constructor), e.g.InvitationRepository
This example shows have I've done this.
Given that I swim in the shallow end of the coding pool, I'm pretty sure there are better ways to accomplish this.
But it worked for me.
YMMV and I HTH