8 ms·

You can have insert/update trigger on views. You shouldn't but you can. More realistically, stored procs would do the CUD parts.

by flukus 7y ago

dragonwriter 7y ago
> 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 7y ago
  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.
  - cryptonector 7y ago
    > 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 7y ago
      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-triggers https://blogs.oracle.com/oraclemagazine/the-trouble-with-tri...
      - dragonwriter 7y ago
        > A method call only ever does one thing at a time, not multiple things in a random order. That's...not at all guaranteed if it is possible for the method call to make use of concurrency and parallelism constructs. It's actually not at all uncommon for method calls to do a unknown number of things in an unknown order (and it can even have an unknown number of them still in progress when the method returns!)
        cryptonector 7y ago
        Exactly.
      - cryptonector 7y ago
        Yeah, and in SQL that's INSERT/UPDATE/DELETE on a table/view. Syntactically, using a stored procedure is really no different, and it can have function calls you don't know about because its body could dispatch just like triggers do. This whole thing about triggers being implied/hidden is not based on anything other than taste.
        taffer 7y ago
        > and it can have function calls you don't know about because its body could dispatch just like triggers do. Please give an example of a stored procedure that does something else than what the code says it will do. > This whole thing [...] is not based on anything other than taste. Good taste: Insert, update and delete doing exactly what the statement says. Procedures doing exactly what the code says. Bad taste: Insert, update and delete surprising you with magic tricks.
  - dragonwriter 7y ago
    > 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 7y ago
      > 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 https://stackoverflow.com/a/1527430 [2] https://www.youtube.com/watch?v=rI8tNMsozo0 https://www.youtube.com/watch?v=rI8tNMsozo0 [3] https://en.wikipedia.org/wiki/Principle_of_least_astonishment https://en.wikipedia.org/wiki/Principle_of_least_astonishmen...
      - cryptonector 7y ago
        Why do you think triggers must be astonishing (but OOP not so)??
        taffer 7y ago
        see https://news.ycombinator.com/item?id=21455027 https://news.ycombinator.com/item?id=21455027
cryptonector 7y ago
> You shouldn't but you can. Shouldn't? Why?
- flukus 7y ago
  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-management/reasons-avoid-triggers 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 7y ago
    A lot of things are non-obvious, especially when you're not aware of them and don't expect them.

You can have insert/update trigger on views. You shouldn't but you can. More realistically, stored procs would do the CUD parts.

by flukus 7y ago

You can have insert/update trigger on views. You shouldn't but you can. More realistically, stored procs would do the CUD parts.

dragonwriter 7y ago

> 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 7y ago
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.
- cryptonector 7y ago
  > 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 7y ago
    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-triggers https://blogs.oracle.com/oraclemagazine/the-trouble-with-tri...
    - dragonwriter 7y ago
      > A method call only ever does one thing at a time, not multiple things in a random order. That's...not at all guaranteed if it is possible for the method call to make use of concurrency and parallelism constructs. It's actually not at all uncommon for method calls to do a unknown number of things in an unknown order (and it can even have an unknown number of them still in progress when the method returns!)
      - cryptonector 7y ago
        Exactly.
    - cryptonector 7y ago
      Yeah, and in SQL that's INSERT/UPDATE/DELETE on a table/view. Syntactically, using a stored procedure is really no different, and it can have function calls you don't know about because its body could dispatch just like triggers do. This whole thing about triggers being implied/hidden is not based on anything other than taste.
      - taffer 7y ago
        > and it can have function calls you don't know about because its body could dispatch just like triggers do. Please give an example of a stored procedure that does something else than what the code says it will do. > This whole thing [...] is not based on anything other than taste. Good taste: Insert, update and delete doing exactly what the statement says. Procedures doing exactly what the code says. Bad taste: Insert, update and delete surprising you with magic tricks.
- dragonwriter 7y ago
  > 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 7y ago
    > 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 https://stackoverflow.com/a/1527430 [2] https://www.youtube.com/watch?v=rI8tNMsozo0 https://www.youtube.com/watch?v=rI8tNMsozo0 [3] https://en.wikipedia.org/wiki/Principle_of_least_astonishment https://en.wikipedia.org/wiki/Principle_of_least_astonishmen...
    - cryptonector 7y ago
      Why do you think triggers must be astonishing (but OOP not so)??
      - taffer 7y ago
        see https://news.ycombinator.com/item?id=21455027 https://news.ycombinator.com/item?id=21455027

cryptonector 7y ago

> You shouldn't but you can. Shouldn't? Why?

flukus 7y ago
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-management/reasons-avoid-triggers 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 7y ago
  A lot of things are non-obvious, especially when you're not aware of them and don't expect them.