In the defence of Object-Relational Mappers
In the defence of Object-Relational Mappers
Event-Driven by Oskar Dudycz
I’m an accidental DBA, but I still never quite got the hate for ORMs. I thought this article does a good job explaining the issue, and why they aren’t so bad.
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I much prefer the repository pattern, as used by sequel and Ecto
Your models are essentially just enhanced structs. They hold information about the shape of data. Generally don't hold any validations or logic related to storing the data. You perform changes on the data using changesets, which handle validation and generating the transaction to persist the data
It works extremely well, and I've yet to encounter the funky problems ActiveRecord could give you
OK, but what about reading the data?
I've never had a problem writing to a database with an ORM. The problems happen when you try to read data (quickly and efficiently).
I agree, it’s even what I mostly use the ORM for, writing is so easy that way and results in far more succinct code.
Data comes out as a map or keyword list, which is then turned into the repository struct in question. If you want raw db data you can get that too. And you can have multiple structs that are backed by the same persistent dataset. It's quite elegant.
Queries themselves are constructed using a language that is near SQL, but far more composable:
Repo.one(from p in Post, join: c in assoc(p, :comments), where: p.id == ^post_id)Queries themselves are composable
query = from u in User, where: u.age > 18 query = from u in query, select: u.nameAnd can be written in a keyword style, like the above examples, or a functional style, like the rest of elixir:
User |> where([u], u.age > 18) |> select([u], u.name)None of these "queries" will execute until you tell the Repo to do something. For that, you have commands like
Repo.allandRepo.one, the latter of which sticks alimit: 1on the end of the provided queryI wouldn't call that "near" SQL, I'd basically just call it SQL. Nothing wrong with that... SQL is great, and using proper language constructs instead of strings makes it even better... but it's not solving the some problem as an ORM.
True, however it occupies the same niche an ORM occupies, without the foot guns. Updating a slew of different db tables from rather clean and straightforward models is relatively simple. It tries to live somewhere between just doing everything as SQL and abstracting everything away like AR does, giving you conveniences from both approaches. You don't get mired in scoping hell, but you don't have big ugly messes of nearly-identical SQL statements either.
i'd recommend trying it out https://hexdocs.pm/ecto/Ecto.html