トランザクション

Reading the Result

For everything you offer to a data holder, the offer method will yield a DataTransactionResult. This object will contain the following:

型

The DataTransactionResult.Type indicates whether the transaction was completed successfully and, if not, how it failed.

UNDEFINED	No clear result for the transaction - indicates that something went wrong
SUCCESS	Transaction was completed successfully
FAILURE	Transaction failed for expected reasons (e.g. incompatible data)
ERROR	Transaction failed for unexpected reasons
CANCELLED	An event for this transaction was cancelled

The affected Data

The result also provides a couple of immutable lists containing immutable value containers representing the data that was involved in the transaction.

successfulData() | contains all data that was successfully set

replacedData() | contains all data that got replaced by successfully set data

rejectedData() | contains all data that could not be set

例

Healing a Player

Surely you remember the healing example in the キーの使用 page. Imagine a player who is down to half a heart (which equals 1 health) being healed that way. The DataTransactionResult in that case would look like this:

• getType() would return SUCCESS

• getRejectedData() would be an empty list

• getReplacedData() would contain one value container for the Keys.HEALTH key with a value of 1.0

• getSuccessfulData() would contain one value container for the Keys.HEALTH key with a value of 20.0

Now what would be different if we used the healing example from the Custom Data page instead? Since the HealthData data manipulator contains values for both the current and the maximum health, in addition to the above result, both the getReplacedData() list and the getSuccessfulData() list would contain one more element: A value container for the Keys.MAX_HEALTH key with a value of 20.0.

Offering HealthData to a block of stone

Now our above-mentioned examples are coded in a such a way that they will fail silently rather than try to offer the incompatible data. But imagine we took a (fully healed) player’s HealthData and tried to offer it to the Location of the stone block he’s currently standing on. We can do this, since Location is also a data holder. And if we do, it would reward us with a DataTransactionResult like this:

• getType() would return FAILURE

• getRejectedData() would contain two value containers for the HEALTH and MAX_HEALTH keys, each with a value of 20.0

• getReplacedData() and getSuccessfulData() would be empty lists

Reverting Transactions

Since everything about a transaction result is immutable, it can serve for documentation of data changes. And it also allows for those changes it documents to be undone. For that, simply pass a transaction result to the data holder’s undo() method. This is particularly useful since some data offerings may be partially successful, so that one or more values are successfully written to the data holder, yet one more value cannot be accepted. Since you may wish to undo the partial successes.

Code Example: Reverting a transaction

import org.spongepowered.api.data.DataHolder;
import org.spongepowered.api.data.DataTransactionResult;
import org.spongepowered.api.data.manipulator.DataManipulator;

public void safeOffer(DataHolder target, DataManipulator data) {
    DataTransactionResult result = target.offer(data);
    if (result.getType() != DataTransactionResult.Type.SUCCESS) {
        target.undo(result);
    }
}