[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.)

[taffer]

> much as you call property setters or getters in OOP languages

Good design is obvious and orthogonal[1]. If you write setters in an OOP language in such a way that they do surprising things, i.e. not just setting a value, then I would call that bad design.

> which is good for loose coupling, modularity, etc.

What do you gain by using triggers in this case? All you get is mental overhead, because whenever you use DML you have to keep in mind that there might be a trigger hiding somewhere that does strange things. If you call a procedure instead, you make it clear that you want to do more than just a simple update or insert.

> [...] it is possible for the method call to make use of concurrency and parallelism constructs [...] to do a unknown number of things in an unknown order

Why would I want this? I want my code simple[2], stupid and obvious, and not convoluted, clever and surprising[3].

[1] https://stackoverflow.com/a/1527430

[2] https://www.youtube.com/watch?v=rI8tNMsozo0

[3] https://en.wikipedia.org/wiki/Principle_of_least_astonishmen...

[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.

[taffer]

You still have to call a method if you want it to do something. It doesn't simply happen as a side effect of something else. A method call only ever does one thing at a time, not multiple things in a random order. Read this if you still think triggers are a good idea: https://blogs.oracle.com/oraclemagazine/the-trouble-with-tri...

[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.