realm-swift: System of object results in duplicates

Goals

I am building a chat application. I want to not have duplicates of my objects

I have mainly 3 objects: a channel, a message and an entity. Both the channel and the message have an entity (the channel can have two) The channel has a primary key, while the message does not (the message has 2 identifiers - a local one and one from the server. when the one from the server arrives, I nullify the temp one. This all means that the Message cannot have a primary key. The problem comes when trying to set a primary key to the Entity class. It doesn’t let me, because if I try to add a message that has attached to it an Entity that already exists in the database (was added because a channel with that entity was added), it crashes.

Expected Results

Have a system that enables me to handle my case. Maybe a custom setter that I can override when adding an Entity to check if it exists already or not.

Actual Results

I got a lot of duplicated instances

Steps to Reproduce

Simple adds of objects

Code Sample

https://gist.github.com/danipralea/e6dc03acd3a8df0e4aeb331bec26d5c8

Version of Realm and Tooling

Realm version: 2.1.2

Xcode version: 8.2

iOS/OSX version: 9.0

Dependency manager + version: 1.2.0.beta.1