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Improves DataAcessObject transaction javadoc

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Rogiel Sulzbach
2011-12-19 17:14:27 -02:00
parent 52820eb92d
commit affa2b6c1a
1 changed files with 53 additions and 0 deletions
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53
l2jserver2-common/src/main/java/com/l2jserver/service/database/DataAccessObject.java
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@@ -22,6 +22,7 @@ import java.util.Iterator;
import com.l2jserver.model.Model; import com.l2jserver.model.Model;
import com.l2jserver.model.id.ID; import com.l2jserver.model.id.ID;
import com.l2jserver.service.core.threading.AsyncFuture; import com.l2jserver.service.core.threading.AsyncFuture;
import com.l2jserver.service.database.DatabaseService.TransactionExecutor;
/** /**
* The Data Access Object interface used used to retrieve, save and remove * The Data Access Object interface used used to retrieve, save and remove
@@ -37,6 +38,58 @@ import com.l2jserver.service.core.threading.AsyncFuture;
* query will be made requesting the given object. In a large dataset, this * query will be made requesting the given object. In a large dataset, this
* could be a huge performance issue. DAO implementations are encouraged to * could be a huge performance issue. DAO implementations are encouraged to
* override the iterator implementation with a more specific implementation. * override the iterator implementation with a more specific implementation.
* <p>
* <h1>Transactions</h1>
* {@link DatabaseService} implementations are required to implement
* {@link DatabaseService#transaction(com.l2jserver.service.database.DatabaseService.TransactionExecutor)}
* which can allow you to perform several operations within a single database
* transaction and have consistency guarantee. Since not all services might
* support transactions, if transaction is not supported, the system degrades
* gracefully and executes the operations outside an transaction. See below an
* example of how to execute in-transaction operations:
*
* <pre>
* final {@link DataAccessObject}<ObjectType1> anyDao1 = ...;
* final {@link DataAccessObject}<ObjectType2> anyDao2 = ...;
* final int rows = {@link DatabaseService databaseService}.{@link DatabaseService#transaction(com.l2jserver.service.database.DatabaseService.TransactionExecutor) transaction}(new {@link TransactionExecutor}() {
* public int {@link TransactionExecutor#perform() perform}() {
* int rows = anyDao1.{@link #insert(Model) insert}(object1);
* rows += anyDao2.{@link #delete(Model) delete}(object2);
* return rows;
* }
* });
* </pre>
*
* If any any operation inside the transaction fails, none of them will be
* commited to the database and its state will be restored previus to the
* execution of the transaction.
* <p>
* <h2>Important note about asynchronous transactions</h2>
* You should not use any of the {@link #insertObjectsAsync(Model...)},
* {@link #updateObjectsAsync(Model...)}, {@link #deleteObjectsAsync(Model...)}
* or {@link #selectAsync(ID)} methods within an transaction. Doing so, will not
* result in exception, though all operations will be performed <b>outside</b>
* the transaction and might not be performed in the declared order. You should,
* instead, make a call to
* {@link DatabaseService#transactionAsync(com.l2jserver.service.database.DatabaseService.TransactionExecutor)}
* in order to execute transactions in an asynchronous manner. Remember, even in
* asynchronous transactions, you should use the synchronous DAO methods. If you
* wish to execute the previus transactions in a asynchronous manner, all you
* need to do is change the <code>transaction</code> method, as shown below:
*
* <pre>
* final {@link DataAccessObject}<ObjectType1> anyDao1 = ...;
* final {@link DataAccessObject}<ObjectType2> anyDao2 = ...;
* final {@link AsyncFuture}<Integer> f = {@link DatabaseService databaseService}.{@link DatabaseService#transactionAsync(com.l2jserver.service.database.DatabaseService.TransactionExecutor) transactionAsync}(new {@link TransactionExecutor}() {
* public int {@link TransactionExecutor#perform() perform}() {
* // note the use of synchronous operations here!
* int rows = anyDao1.{@link #insert(Model) insert}(object1);
* rows += anyDao2.{@link #delete(Model) delete}(object2);
* return rows;
* }
* });
* final int rows = f.{@link AsyncFuture#get() get}();
* </pre>
* *
* @param <O> * @param <O>
* the {@link Model} supported by this DAO * the {@link Model} supported by this DAO