[stefanchrobot]

Somebody in our team put this on production. I guess this solution has some merits if you need something quick, but in the long run it turned out to be painful. It's basically SQL over REST. Additionally, your DB schema becomes your API schema and that either means you force one for the purposes of the other or you build DB views to fix that.

[cryptonector]

> or you build DB views to fix that.

That's what VIEWs are for! Well, one use-case of VIEWs, anyways.

There's nothing wrong with the schema as the API since you can use VIEWs to maintain backwards compatibility as you evolve your product.

Put another way: you will have an API, you will need to maintain backwards compatibility. Not exposing a SQL schema as an API does not absolve you or make it easier to be backwards-compatible.

You might argue that you could have server-side JSON schema mapping code to help with schema transitions, and, indeed, that would be true, but whatever you write that code in, it's code, and using SQL or something else is just as well.

[mycall]

How do you do CRUD with views? I know Reads are what views do.

[dragonwriter]

> How do you do CRUD with views? I know Reads are what views do

Both automatically updatable views (supporting insert/update/delete by default because their structure provides a clean mapping to the backing table) and views made updatable through instead-of triggers exist in Postgres.

[cryptonector]

  CREATE TRIGGER <name>
  INSTEAD OF INSERT OR UPDATE OR DELETE
  ON <view-name> ..

[flukus]

You can have insert/update trigger on views. You shouldn't but you can.

More realistically, stored procs would do the CUD parts.

[dragonwriter]

> You can have insert/update trigger on views. You shouldn't but you can.

You can, and there is no reason you shouldn't.

> More realistically, stored procs would do the CUD parts.

Why are stored procs more realistic?

[taffer]

Triggers are implicit, have side effects and are not deterministic. They are confusing and surprising.

A procedure call is explicit, a trigger is implicit. You don't call a trigger, it just happens as a side effect of something else. People tend to forget implicit things. Suddenly you notice that something is acting strangely or slowly in your application. You can look at your functions and procedures and try to find the problem. But if your application has triggers all over the place, how do you know what is going on? A trigger can change a dozen rows, which in turn can change other rows, so changing a single row can fire thousands or millions of triggers. Also, triggers are not fired in a particular order, the database is free to change the query plan according to what it thinks is best at the moment, so triggers are not deterministic. Triggers can sometimes work and sometimes not.

Almost everything that can be done with a trigger can be done with a procedure, but explicitly, deterministically and in most cases without side effects.

[dragonwriter]

> You don't call a trigger

You call an instead of trigger implementing updatability of a view, or the select query defining a view, just as much as you call property setters or getters in OOP languages.

With the DB triggers, as in many OOP languages (C#, Python), this is an implementation detail obscured from the calling site, which is good for loose coupling, modularity, etc.

Your objections, while IMO still overblown, have relevance to some uses of triggers (they are particularly applicable to AFTER triggers and BEFORE triggers other than those implementing constraints, but least applicable to INSTEAD OF triggers implementing view updatability, which is what we are discussing here.)

[cryptonector]

> Triggers are implicit, have side effects and are not deterministic. > ... > A procedure call is explicit, a trigger is implicit.

Method dispatch (whether the language be OOP or otherwise) is also "implicit".

Think of triggers as controlled code injection.

[cryptonector]

> You shouldn't but you can.

Shouldn't? Why?

[flukus]

They're non-obvious and can bite you in several ways. A lot has been written about why triggers are bad (random example: https://www.itprotoday.com/development-techniques-and-manage...). Back before service layers were common and desktop clients connected to the database directly they were common and just about everyone has some war stories of triggers breaking things.

[cryptonector]

A lot of things are non-obvious, especially when you're not aware of them and don't expect them.

[ruslan_talpa]

what's wrong with views (which should have been used formt he start)? What were the pain points?

[bdcravens]

They are great when used well, but non-materialized views can kill performance with large data sets.

[doh]

That's the same as saying "unoptimized selects can kill performance with large data sets". Of course they can. That's what optimization is for.

We have quite large amount of data (100TB+ and trillions of rows at this point [0]) and no problem with views.

[0] https://www.citusdata.com/customers/pex

[ruslan_talpa]

a view is nothing but a query, so if the view is "killing" the performace for you, running the same query from the client will not change anything, the porformance will get "killed" in the exact same way.

[bdcravens]

Yes, if you are running the same query. Some of the worst use of views I've seen involve massive joins without filters, and then filtering further down, so you end up working with a recordset in the millions of records rather than a few thousand.

[ruslan_talpa]

I understand the problem you are describing, i would say that is a wrong type of view to create, if one plans to write filters on top of that view then it should be written so the filters can be inlined in the view (which would basically give you the finished query you would be sending from the layer above)

[philwelch]

That kind of reminds me of the classic doctors joke though. If it hurts when you do that, don't do that.

[sk5t]

It's kind of unclear what problem you are trying to describe. Views shouldn't confound the query planner, and creating views with "filters" sounds like probably a mistake--query the view with the predicates you need then.

[aidos]

So filtering later outside of the db? If you filter on a view the optimiser should be able to sort it out - as others have mentioned, it’s no different from a regular query.