Custom relationship between instances

[nikola-zivkov]

Question

Hi @simonbrowndotje

I have a problem which is similar to that discussed in #39.

The best way to describe my problem is to use your "Big Bank plc" live deployment diagram. Namely, is it possible to have a different text in the relationship between the "API Application" instance and the "Secondary Database" instance?. More specifically, I would like for the text in that relationship to be "Reads from" while the one between the "API Application" instance and the "Primary Database" instance to remain "Reads from and writes to".

Thanks,
Nikola

[simonbrowndotje]

I would suggest creating two relationships in the static model (Reads from and Reads from and writes to), and including/excluding them as appropriate on the deployment views between the various instances of your containers. After all, from a modelling perspective, you essentially have two different relationships, which I'm guessing are enabled by something like a configuration switch at deployment time.

[nikola-zivkov]

I did add both of them in the model, but I'm failing at excluding the "Reads from" in the relation to the primary database instance, and the "Reads and writes to" from the relation to the secondary database instance - there are two "Reads from" and two "Reads and writes to" relation instances but I only need to keep one of each.

How do I exclude a relation instance rather that a relation from the model it self, which would exclude both instances? There is no configuration switch, both relations are active at the same time, but towards different database instances.

P.S. I'm explaining deployment diagrams to my team tomorrow, and hope to not to have to tell them that this is something that is not supported :)

[simonbrowndotje]

I'd be tempted to model the read/write and read-only databases as separate containers, which then makes what you're trying achieve easier. That said, the following will work (I don't know why && isn't in the docs):

workspace {

    model {
        softwareSystem = softwareSystem "Software System" {
            app = container "App"
            db = container "Database"

            r1 = app -> db "Reads from and writes to" {
                tags "Read/Write"
            }
            r2 = app -> db "Reads from" {
                tags "Read-Only"
            }
        }
        
        env = deploymentEnvironment "env" {
            deploymentNode "Server 1" {
                appInstance = containerInstance app
            }

            deploymentNode "Primary Database Server" {
                primaryDBInstance = containerInstance db
            }

            deploymentNode "Secondary Database Server" {
                secondaryDBInstance = containerInstance db
            }
        }
    }

    views {
        deployment * env {
            include *
            exclude "appInstance->primaryDBInstance && relationship.tag==Read-Only"
            exclude "appInstance->secondaryDBInstance && relationship.tag==Read/Write"
            autolayout
        }
    }
    
}

[nikola-zivkov]

Perfect, exactly what I was after.

There is already something something in the documentation that suggests this is possible ("relationship.tag==,[tag]") but I guess it didn't occur to me that I can combine the two expressions with the "&&" operator.

One more thing, risking on being accused on nitpicking here, but wanted to point out that it's not possible to use empty spaces before and after the "==" operator, like "relationship.tag == ,[tag]". I noticed this when I tried to apply a similar formatting like I have with the "->" operator, but perhaps this is by design.