What are the arguments for and against business logic in stored procedures?
Against stored procedures: business logic in programming space
I place a high value on the power of expression, and I don't find the SQL space to be all that expressive. Use the best tools you have on hand for the most appropriate tasks. Fiddling with logic and higher order concepts is best done at the highest level. Consequently, storage and mass data manipulation is best done at the server level, probably in stored procedures.
But it depends. If you have multiple applications interacting with one storage mechanism and you want to make sure it maintains its integrity and workflow, then you should offload all of the logic into the database server. Or, be prepared to manage concurrent development in multiple applications.
I am thoroughly against it. One of the biggest reasons is the first reason earino stated - it lives in one place. You can not integrate it into source control very easily. It is next to impossible to have two devs working on a stored proc at the same time.
My other main complaint is that SQL is just not very good at representing complex logic. You have no concept of scope, code tends to be copy-pasted because there is a less ability to reuse code (as opposed to an OO language).
You have to give developers access to the database to develop there. In many organizations I have worked at the data people are in a different world than the devs, with different permissions, etc. Keeping the devs out of the database in these cases would be harder.
I'm of the school of thought that says that as long as business logic:
- lives in one place
- where it is properly documented
- proper access is provided through services that can be loosely coupled
- through a published abstracted interface
I don't care if the logic lives in a stored procedure, in a J2EE middle tier, in a clips expert system, or wherever. No matter where you store our business logic the "law of conservation of misery" is going to guarantee that someone will say it was the wrong idea because component/repository X needs to be swapped out for technology/method Y.
Some thoughts: Please note this is a Java centric response, but its the bulk of my recent (last 10years) experience
(1) Concurrent development by a (a large) team of developers. If you're application is sufficiently complex that each developer can't set up their own private version of the DB (with attended links/ref data/etc...)it is very difficult to have an entire TEAM of developers all working on the same set of PL-SQL (for example) packages at the same time stored in a shared DEVL DB? Then your stuck (my experience) with working in a DB with invalid procedures / mismatch of code to tables as people make changes...
As a Java architect, I think its much easier to have each developer have a private JBoss instance on their desktop and work easily on their own set of functionality, and integrating at their own pace without impacting everyone else ... which brings me to ...
(2) Continuous Integration toolsets While there exist some similar 'concepts' in the DB world, my experience has shown me that the combo of (i'm picking my current best-of-breed favs here):
- mvn - build system
- junit - automated unit testing
- nexus - repo manager (manages artifact's lifecycles version, snapshots and releases)
- hudson - ci build server
- sonar - static analysis tool / code coverage reports / ALOT more
Running a large project using all of the above (free tools) allows a consistent / easy way to deliver XP to the masses and enforce quality controls over a whole IT staff. Oracle / PL-SQL doesn't have the toolsets to match
(3) tools / libraries / etc... Java has access to an amazing set of services that other platforms cannot touch - some free, some not. even basic ones, like log4j (yes they have it for PL/SQL, but pulease...its not nearly the same) allows for things like allowing developers to create flexibly adjustable logging that can be changed on the fly (perfect for dubugging). Automated API documentation (via javadoc). Automated unit test coverage reports. Incredible IDEs (Eclipse) with integrated debuggers / autodeploy to app servers. An API to interface with every type of service under the sun, open source libraries to do ANYTHING, and 100% support by every vendor
(4) reuse of services. what someone commented on is true. If you have heavy duty data driven business rules then you can argue that these should live in the DB layer. Why? to prevent having the middle tier(s) all having to duplicate that logic.
But the same can be said for business rules that are not data driven or sufficiently complex that OO is a more natural choice. If you stick ALL business logic in the DB, then they're available only via the DB.
- What if you want to have validation done in the client or middle app tier and save a round trip to the DB?
- What if you want to cache read only data in the middle tier (for performance) and have business rules execute against the cached data?
- What if you have a middle tier service that doesn't require DB access, or you have a client that can supply their own data?
- What if the data dependent portion of the business rules then needs to access external services? Then you end with with fragmented business logic that looks like this:
i
retCode = validateSomeDate(date);
if (retCode == 1) then
evaluateIfCustomerGetsEmail(...)//probably more stored proc invocations here...
sendEmailMsg(....)
else if (retCode == 2) then
performOtherBizLogicStuf(...) //again, may need data, may not need data
triggerExternalsystemToDoSomething(...) //may not be accessible via PL/SQL
fi
I'm sure we've all seen systems written like the one above and had to debug them at 2AM. Its extremely difficult to get a coherent sense of a complex process when the business logic is fragmented between tiers, and in some cases it gets to be impossible to maintain.
"You can not integrate it into source control very easily." - if you put the code that creates the stored proc into a script that's version controlled, that objection goes away. If you follow Scott Ambler's agile database ideas, that's exactly what you should be doing.
Not all developers are good data modelers. I can think of horrible schemas created by developers who thought that a dabbling knowledge of SQL made them database experts. I think there's a lot of value to having developers working with DBAs and data modelers.
If only one application uses the database, I'd say that business logic can appear in the middle tier. If many apps share the database, perhaps it's better to put it in the database.
SOA offers a middle way: services own their data. Only the service has access to the data; getting to data means going through the service. In that case, it's possible to put the rules in either place.
Applications come and go, but data remains.
One more reason NOT to store business logic in sprocs - limited scaling abilities of the DB. It is very common situation where your database is your bottleneck, that is why it is a good idea to take as much load of the DB as possible.
My few observations:
In favour of stored procedures:
after some time of project life, in most cases the bottleneck is the database not the web server - and stored procedures are much, much faster
using sql profiler with ORM generated sql queries is very difficult; this is easy with stored procedures
you can deploy a fix for stored procedure instantly, without a service window
for performance, it is easier to optimize a stored procedure than ORM-code
you may have many applications using the same db / stored procs
any complex data scenario is a vote for stored procedures
In favour of application/ORM:
you may use code repository (with stored procs it is still possible but expensive)
java / c# language is a better tool to express business logic
java / c# is easier to debug (except for the dynamically-generated ORM sql)
independence of database engine (however this is not very likely that a project will change database to another one)
ORM provides data model which is easy to use
In my opinion: for large projects - go for stored procedures, for the others - Application/ORM will work fine.
In the end of a day, the only thing which matters is the database.
Business logic should be encapsulated in one place. We can guarantee that the logic is always run and run consistently. Using classes that all activity involving an entity on the database must run through we can guarantee that all validation is run properly. There is one place for this code and any developer on the project can easily open this class and see the logic (because documentation can and does get out of date, the code is the only reliable form of documentation).
This is difficult to do with stored procedures. You may have more than one sproc dealing with the same table(s). Chaining multiple sprocs together so that the logic resides in only one gets unwieldy. That is strike one. How do you determine "What are all of the business rules surrounding entity X" within the database? Have fun searching thousands of sprocs trying to track that down.
Number two is that you are tying your business logic to your persistence mechanism. You may not store all of your data in the same database, or some may reside in XML etc. This type of inconsistency is difficult on the developer.
Validation is difficult to perform if the logic resides only in the database. Do you really call a sproc to validate every field on your data entry form? Validation rules and business logic are close cousins. This logic should all be performed in the same place!
+: SQL server sometimes optimizes the code
+: You are forced to pass parameters, which limits SQL injection issues
-: Your code depends on a single database (some dbs don't even have SP)
-: To change code you need to connect to database
-: Logic is not organized well
Personally I'm against it, but I had to use it once on a really busy website. Using SP in MS SQL brought huge benefits, but once I implemented caching those benefits were not so big anymore.
There is a saying...
When all you have is a hammer, everything looks like a nail.
In my humble opinion there is no one answer that will fit all circumstances. It seems to me that many people just assume that putting Business Logic in the database is always wrong.
A lot of work has been done to make transaction processing, especially bulk operations, very efficient when done on the database side. Also the code management in databases has vastly improved since most of the opinions against databases were formed.
I think it is wrong to consider the database server as just a persistence layer. If your processing activities are most efficient when done on the DB Server then do them there.
If not then do them elsewhere.
It all comes down to what best fits the application you are working on at the moment, the team with whom you are working and the customer who hired you.
That just my 2 cents.
You can unit test business logic when its in a business logic layer. If it's completely separate the persistance operations can be mocked so you are testing the BL only. A stored proc is far more difficult to maintain/debug/unit test than e.g. linq and c#.
DBMS != Application server
- Functional programming (DB Stored procedure) vs OOP. For big programs is OOP just standard.
- IDE - eclipse, intellij, netbeans with all plugins for debugging, testing and analysis works only with real programming languages. Static code tools.
- Version control if you get one for PLSQL & co. is great. If you get "synchronize view" direct from you IDE - you are real the lucky one.
- Scale your system. For DB system is hell. You need expensive hardware for other "nodes". Replication. And probably licence for every node. Don't forget you are still in "functional programming" and effort to understand and maintain such systems is much bigger.
- You are stuck with your DB, try to change or add a new one from another company
- And so on...
Stored procedure for business logic is bad practise today. Use 3-Tier architecture instead.
Performance will be massively improved by moving logic into the stored procs, especially if explicit transactions are involved.
In my experience, application developers aren't very good at writing optimised database code, and don't tend to think about concurrency or performance issues.
If business logic is kept in the application layer, you tend to have to shift large amounts of data (often in many round-trips) across the network, duplicate it in memory on the DB server, and at least once in the app server, and do a load of row-by-row processing in the app while you're holding open a transaction. Then the app developers complain that the database is slow and keeps deadlocking.
If you put the logic in the DB wherever it's possible, you tend to just pass a few parameters across the network, transactions aren't held while you wait for network resources, and the whole thing goes like greased lightning. Databases should of course go in source control like any other source code.. there are plenty of tools for that.
@Nick "I am thoroughly against it. One of the biggest reasons is the first reason earino stated - it lives in one place. You can not integrate it into source control very easily. It is next to impossible to have two devs working on a stored procedure at the same time."
Not that I'm arguing for putting business logic on stored procedures (all the contrary). But these reasons you put forward make no sense. A stored procedure is simply a sql/DDL artifact that can be stored on source control, and which is also a deployment artifact (that is, something handed over to the dba for deployment, much the same way you would hand over your war/ear artifacts to the IT/deployment liasons) One or more developers can work on the same stored procedure off source control just in the same way you'll do with plain old source code - by branching, versioning and merging.
Now, if the only copy of the stored procedure (and the packages that contain them) only exist in the database, then obviously you cannot control that with source control (and all the problems associated to that). However, that's not a problem of stored procedure but a problem of ineptitude in regard of how to use that code. It is as equally a display of ineptitude as having only one copy of your source code living on production.
I've worked in systems with massive amounts of code, both Java and PLSQL/DDLs and they were all versioned on clearcase. They were all treated as source code that would be compiled and deployed with a strict process, with different teams working on them. Never had any problem as what you are describing.
There are context-specific reasons not to put business logic in stored procedures, but these aren't valid ones.
High budget projects: If you are keeping your up to date data in memory and saving the changes to disk periodically, you would want to handle business logic apart from the db server. use case: serve data from ram, complex caching mechanisms.
Low budget projects: If you are keeping the up to date data on disk and your presentation is dependent on disk reads, handling business logic in stored procedures can save you development time. use case: serve data from disk
There are different kinds of "business logic". Consider partitioning it based on how it's related to other layers or services. Here are some rules of thumb from an MVC perspective:
a) In the database (stored procedure) if it's mostly data-related, and can be done with joins and relatively simple WHERE and SELECT clauses.
b) In the controller if it's mostly routing or dispatching related; that is, larger-scale UI flow control in terms of screen or resource selection.
c) In the model or view-model if it involves complex or intricate computations and/or conditionals.
d) In the view (such as Razor) if it's primarily a display issue, such as "friendly" re-formatting and relatively simple to implement. (If it's complex, consider putting it in a view-model.)
My rule of thumb (once I recognized what it was by thinking about the question) is that stored procedures should contain code that ensures data integrity within the database, whether the stored procedure prohibits certain data insertion, deletion or modification, or makes other changes necessary for data consistency. Business logic, especially logic that cannot be implemented in a handful of set-based operations, should be implemented elsewhere. Databases are not applications. Databases should be the ultimate authority for relationships and constraints, even if the business rules are also implemented elsewhere for, say, the provision of feedback in user interface code that reduces postbacks from a web server or eliminates otherwise unnecessary hits on a busy server. One can argue whether "data consistency" includes the result of complex processing of complex business rules, but I think it's usually clear once the context is understood. Not all business rules are implemented as data relationships or constraints. Not all operations in a stored procedure are faster than code running in a separate process, even on a process running on a separate machine across a network. I recently did a demonstration showing that many operations in SSIS, for example, (INSERT INTO () SELECT FROM) perform faster in SSIS running across a network on a separate machine than running in a stored procedure (that also inserts the results to a database across the network). This is an almost unbelievable result (where SSIS is faster than raw SQL statements), and demonstrates that the discovery of the best optimization of any performance issues comes from reality (testing) and not from logic based on only a few concepts. (We still have to make decisions on what to test by rules of thumb learned by experience.) (SSIS performed faster by automatically implementing multithreading and pipelines, using BULK INSERT even where it wasn't specified in the raw SQL statement, and sending batches of inserts on one thread while creating additional BULK INSERTs on other threads. In this instance, it performed about twice as fast as raw SQL statements.) When I used to teach programming and SQL Server courses, PowerBuilder users seemed to have the statement "Native drivers provide the fastest data access" burned into their tongue, and while it might be justified through additional (unrecognized by them) explanation, the thinking behind it is misleading.
来源：https://stackoverflow.com/questions/484516/arguments-for-against-business-logic-in-stored-procedures