Generate Mermaid class diagram (or expose DAG) from schema

[ingun37]

What is the problem this feature would solve?

Developers want to visualize and document their data schema, likely in UML Class diagram. For those who define their type in the traditional way would have to draw the diagram manually, and it's a big maintenance cost.

What is the feature you are proposing to solve the problem?

A function that takes a schema and generate Mermaid Class Diagram. It will be particularly useful for developers who document their domain logic in GitHub Markdown because they supports Mermaid.

What alternatives have you considered?

writing manually

[ingun37]

I would love to make a PR myself if you'd approve making this feature and give me some guidance.

[gcanti]

Could you please provide an example including the schemas and the expected diagram?

[ingun37]

@gcanti Here are some rules I'm thinking

• Annotation of properties and types follows typescript syntax
• Omit access specifiers (public +, private -)
• Unify the relation between entities with Association rather than using aggregation or composition for the simplicity. Because I don't think there's distinction of have-relations in Schema.
• Optional, N-to-N relations are expressed with cardinality.
• Discriminated types are expressed with inheritance. Maybe group them with namespace for the readability
• For Struct, use annotation to know its name. For Class, use unique identifier

const Person = Struct({
  name: Schema.Number,
  age: Schema.String,
  religion: Schema.optional(Schema),
  degrees: Schema.Array(Degree),
}).annotations({ title: "Person" })

const Religion = Struct({
  name: Schema.String
}).annotations({ title: "Religion" })

const Bachelor = Schema.Struct({
  kind: Schema.Literal("bachelor"),
}).annotations({ title: "Bachelor" })

const Master = Schema.Struct({
  kind: Schema.Literal("master"),
  thesis: Thesis
}).annotations({ title: "Master" });

const Thesis = Schema.Struct({}).annotations({ title: "Thesis" })

const Degree = Schema.Union(Bachelor, Square).annotations({ title: "Degree" })

classDiagram
class Person {
  name: string
  age: number
  religion?: Religion
  degrees: Degree[]
}
class Religion {
 name: string
}
namespace Degrees {
class Degree {
  kind: "master" | "bachelor"
}
class Master {
  kind: "master"
  thesis: Thesis
}
class Bachelor {
  kind: "bachelor"
}
}
class Thesis
Person --> Religion
Person "1" --> "*" Degree
Degree <|-- Master
Degree <|-- Bachelor
Master --> Thesis

(I notated cardinatily but it's not rendering. I guess it's a current bug.)

[fubhy]

That's a DAG. So we first need graph data structures in Effect. Deriving a mermaid representation from a DAG is trivial

[gcanti]

@fubhy It depends on the meaning assigned to the edges. For instance, if the directed edge represents the relation "this schema uses this schema" then it's not acyclic (counterexamples: recursive schemas, mutually recursive schemas)

[fubhy]

True. I was just refering to this specific example. My point is, I would like to have graph data structures in effect modules. For various types of graphs. Once we have those, rendering them with mermaid is trivial, whether it is a DAG or not. My second point was that, from an api design standpoint, I think it would be desirable to go schema -> graph -> mermaid instead of schema -> mermaid.

[ingun37]

If you could expose underlying graph data structure then I guess I could achieve the same thing. I'll appreciate that too.