Does it make sense mark with spring's #Transactional a method with a single save sentence?
For example:
// does it make sense mark it with #Transactional if it only has 1 save sentence?
#Transactional
public void saveMethod() {
user.save()
}
If you´re using Spring data interface, you dont need use #transactional annotation. Only in case that you want to provide two execution against the database and you want to share the transaction, so then rollback of both actions can be made.
Anyway it is always better use #transactional even as read-only for get queries(setting the FlushMode to MANUAL to let persistence providers potentially skip dirty checks when closing the EntityManager), so I would suggest put the #transactional as Service layer and read-only for get queries.
Yes because any "modifications" on the database requires a transaction (to commit the changes). You might think otherwise because of auto-commit, but in the end, there is still a transaction there somewhere.
But it is always a good thing to explicitly define the boundaries of your transaction (when transaction is started and when it is committed).
Related
I used Spring Boots #Transactional on the Service Layer to avoid the Lazyinitializationexception. But is there an advantage of using #NamedEntityGraph instead of #Transactional to avoid Lazyinitializationexception?
#NamedEntityGraph not only avoid Lazyinitializationexception but also helps optimizing the number of requests sent to avoid N+1 effect. This may be a valuable advantage but needs more work to ensure that every needed object will be fetched before the end of the hibernate session.
I am using EntityManger for the retrieval queries in my spring boot application. An example snippet is given below.
#Repository
public class EntityManagerUtil {
#PersistenceContext
private EntityManager entityManager;
public List<Employee> getAll(){
// Use entityManager here
}
}
I need some clarity on the below questions.
a. Is EntityManger will be created for every call (or) will it be a singleton? (I tried printing entityManager, it is returning the same object for all the calls)
b. Is this approach leads to any connection leaks?
c. Do I need to put #Transactional annotation on reading operations?
I am using spring boot version 2.0.3-release
a) See M Deinum's comments about the injected EntityManager being a proxy. The normal situation for JPA is to have an EntityManager tied to each thread, Spring sets this up for you and provides a proxy to delegate to the actual EntityManager. So this arrangement is safe.
b) Connection leaks happen when you don't return a database connection to the pool. Spring takes care of providing a connection and cleaning up resources so in the normal course of things you shouldn't get connection leaks. If you ignore the facilities Spring gives you like JdbcTemplate and insist on writing your own JDBC code, then you can cause resources to leak. If your code tries to use an EntityManager intended for another thread you will get an exception, it will not fail silently, and it will not (in itself) cause a connection leak.
c) You are using an RDBMS so you will have a transaction.
Apparently some people think transactions are optional, but they really aren't. If you don't specify them then Spring will wrap each operation in its own transaction. Not only are you just better off in general being explicit about this, but you can mark the transaction as readonly, which lets Spring perform some optimizations, see Oliver Drotbohm's answer for details. So maybe you can get by without it for some cases (such as, each http request results in only one database operation), but it is in your interest to use it.
I want to persist some data after an exception occurs in ItemWriter step. But if I am not incorrect, in this case a rollback would happen and so this persisting logic won't work.Is there any way to achieve this?
Right now, I am implementing itemWriteListener and all the persisting logic is written inside onWriteError method. This logic only concerns to change state of some entities to error.
You'll want to use a separate connection that does not participate in the transaction. For example, inject a DataSource into your listener and construct your own JdbcTemplate with an independent connection. By doing that, the writes should not be rolled back.
If you mark the onWriteError method with
#Transactional(propagation = Propagation.REQUIRES_NEW)
...would this work as well?
I would like to understand that if I annotate my junit class with #Transactional, Spring will create only one transaction which will be shared among my #Test methods and rolled back at the end. Whereas if instead I mark each single #Test with #Transactional, a new transaction will be created and rolled back on a #Test basis. I didn't quite find the expected behaviour in the official documentation (link).
Putting #Transactional on a class level is equivalent to putting it on each of the test methods.
I don't think there is an easy way of achieving your first scenario, ie, a single transaction for all the tests. I am not sure it would make much sense anyway since tests will be executed in a random order so you cannot rely on seeing each others modifications. Of course you can always explicitly call your methods from a single uber-test with a single transaction.
#Transactional at JUnit test case class level will start new transaction before each test method and roll it back afterwards.
You cannot easily start new transaction at the beginning of test class and keep it open for the whole class, at least Spring is not supporting this. Your first workaround would be to use #BeforeClass/#AfterClass pair, but they must be static thus you don't have access to transactional manager.
But first ask yourself a question, why do you want to do this? Sounds like one test depends on the output or database side effects of the other. This is a big anti-pattern in testing, not to mention JUnit does not guarantee the order in which test methods are executed. Maybe you just need a database setup before each test case? #Before and #After are executed within the context of Spring transaction, so you can use them there.
In a Grails app, the default behaviour of service methods is that they are transactional and the transaction is automatically rolled-back if an unchecked exception is thrown. However, in Groovy one is not forced to handle (or rethrow) checked exceptions, so there's a risk that if a service method throws a checked exception, the transaction will not be rolled back. On account of this, it seems advisable to annotate every Grails service class
#Transactional(rollbackFor = Throwable.class)
class MyService {
void writeSomething() {
}
}
Assume I have other methods in MyService, one of which only reads the DB, and the other doesn't touch the DB, are the following annotations correct?
#Transactional(readOnly = true)
void readSomething() {}
// Maybe this should be propagation = Propagation.NOT_SUPPORTED instead?
#Transactional(propagation = Propagation.SUPPORTS)
void dontReadOrWrite() {}
In order to answer this question, I guess you'll need to know what my intention is:
If an exception is thrown from any method and there's a transaction in progress, it will be rolled back. For example, if writeSomething() calls dontReadOrWrite(), and an exception is thrown from the latter, the transaction started by the former will be rolled back. I'm assuming that the rollbackFor class-level attribute is inherited by individual methods unless they explicitly override it.
If there's no transaction in progress, one will not be started for methods like dontReadOrWrite
If no transaction is in progress when readSomething() is called, a read-only transaction will be started. If a read-write transaction is in progress, it will participate in this transaction.
Your code is right as far as it goes: you do want to use the Spring #Transactional annotation on individual methods in your service class to get the granularity you're looking for, you're right that you want SUPPORTS for dontReadOrWrite (NOT_SUPPORTED will suspend an existing transaction, which won't buy you anything based on what you've described and will require your software to spend cycles, so there's pain for no gain), and you're right that you want the default propagation behavior (REQUIRED) for readSomething.
But an important thing to keep in mind with Spring transactional behavior is that Spring implements transaction management by wrapping your class in a proxy that does the appropriate transaction setup, invokes your method, and then does the appropriate transaction tear-down when control returns. And (crucially), this transaction-management code is only invoked when you call the method on the proxy, which doesn't happen if writeSomething() directly calls dontReadOrWrite() as in your first bullet.
If you need different transactional behavior on a method that's called by another method, you've got two choices that I know of if you want to keep using Spring's #Transactional annotations for transaction management:
Move the method being called by the other into a different service class, which will be accessed from your original service class via the Spring proxy.
Leave the method where it is. Declare a member variable in your service class to be of the same type as your service class's interface and make it #Autowired, which will give you a reference to your service class's Spring proxy object. Then when you want to invoke your method with the different transactional behavior, do it on that member variable rather than directly, and the Spring transaction code will fire as you want it to.
Approach #1 is great if the two methods really aren't related anyway, because it solves your problem without confusing whoever ends up maintaining your code, and there's no way to accidentally forget to invoke the transaction-enabled method.
Approach #2 is usually the better option, assuming that your methods are all in the same service for a reason and that you wouldn't really want to split them out. But it's confusing to a maintainer who doesn't understand this wrinkle of Spring transactions, and you have to remember to invoke it that way in each place you call it, so there's a price to it. I'm usually willing to pay that price to not splinter my service classes unnaturally, but as always, it'll depend on your situation.
I think that what you're looking for is more granular transaction management, and using the #Transactional annotation is the right direction for that. That said, there is a Grails Transaction Handling Plugin that can give you the behavior that you're looking for. The caveat is that you will need to wrap your service method calls in a DomainClass.withTransaction closure and supply the non-standard behavior that you're looking for as a parameter map to the withTransaction() method.
As a note, on the backend this is doing exactly what you're talking about above by using the #Transactional annotation to change the behavior of the transaction at runtime. The plugin documentation is excellent, so I don't think you'll find yourself without sufficient guidance.
Hope this is what you're looking for.