So why not just use a RDMS from day one?
When I did implement a system with C#/Mongo, I fell in love with changing my database schema just by changing my C# objects. With the C# driver you can include a Dictionary as part of your object to round trip unmapped fields.
Not to mention that after you go through all of your modeling and figuring out your aggregate roots, you can just store the entire object graph with one .Add and the entire object is stored atomically without having to worry about transactions, table locks, etc.
Unlike with an RDMS where your beautiful aggregate root has to constantly be composed and decomposed.
I think it’s just going to take somebody shaking the cobwebs off of their X.500 manuals and making the query syntax and schemas a little more ergonomic for them to come back en vogue.
It’s one thing to have the ability to mold your DB to model hierarchical data but have your DB engine support it non-awkwardly might be a game changer. People are already used to apps needing a DB, cache, queues, S3, filesystem, service discovery, that adding one more thing would hardly break the bank.
Why use a relational store? If you’re working with a system that will only be read and written by an object based language? Why keep converting back and forth between a relational model and an object oriented model?
In C#
var seniorMales = from c in context.Customers
where c.Age > 65 && c.Sex == “M”
You get autocomplete and compile time checks.
When you want to add an record to your Mongo collection, you work with strongly typed
IMongoCollection<Customer>
Anything that you can store in object database you can normalize and store in an RDMS. ORMs have been translating relational models back and forth to object models for decades.
In the case of Mongo, you just create one object containing other objects, lists, arrays etc and the driver serializes it to a JSON like structure and stores it as is in the collection.
In the case of an RDMS, you create your C# classes to model your tables and relationships.
The driver translates the LINQ to the appropriate query language.
Well I can't tell you what the right choice in your system is, but in the general case I think going with a relational model by default generally makes sense because it's rather future proof. By that I mean a relational model gives you the most flexibility in the future to evolve your system in ways you couldn't/didn't anticipate when the system was initially designed.
No point using a relational db for that kind of thing.
Not to mention the LINQ driver....
And you can’t do updates on individual JSON fields in Postgres.
The problematic part with PostgresSQL JSONB is modifying a JSONB column content. In any case, we totally replace the old content by a new one. So, the update operations turn to the complex queries that can lose the content. You can avoid this by performing the full JSON reorganization before the persistent operation.
You still don’t have the richness of MongoQuery and the aggregation framework and the tooling around working with JSON data isn’t there. Let alone the native driver support.