Hi there, We've run into an issue whereby, we receive a ClassCastExc

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Class Cast Exception when attempting to utilize Try<T> about java-dataloader HOT 5 CLOSED

graphql-java commented on June 13, 2024

Class Cast Exception when attempting to utilize Try

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Comments (5)

spitty commented on June 13, 2024

Hi @kaseyreed,

Are you using java-dataloader:2.0.2?
Could you please attach exception with stacktrace to this issue?

If it possible please provide us with minimal reproducible code example.

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kaseyreed commented on June 13, 2024

@spitty

Yes, we are using java-dataloader:2.0.2

Here is a stacktrace:

java.lang.ClassCastException: com.myCompany.MyType cannot be cast to org.dataloader.Try
	at java.util.concurrent.CompletableFuture.uniApply(CompletableFuture.java:602)
	at java.util.concurrent.CompletableFuture$UniApply.tryFire(CompletableFuture.java:577)
	at java.util.concurrent.CompletableFuture.postComplete(CompletableFuture.java:474)
	at java.util.concurrent.CompletableFuture.complete(CompletableFuture.java:1962)
	at org.dataloader.DataLoader.lambda$dispatchQueueBatch$3(DataLoader.java:328)
	at java.util.concurrent.CompletableFuture.uniApply(CompletableFuture.java:602)
	at java.util.concurrent.CompletableFuture$UniApply.tryFire(CompletableFuture.java:577)
	at java.util.concurrent.CompletableFuture.postComplete(CompletableFuture.java:474)
	at java.util.concurrent.CompletableFuture$AsyncSupply.run$$$capture(CompletableFuture.java:1595)
	at java.util.concurrent.CompletableFuture$AsyncSupply.run(CompletableFuture.java)
	at java.util.concurrent.CompletableFuture$AsyncSupply.exec(CompletableFuture.java:1582)
	at java.util.concurrent.ForkJoinTask.doExec(ForkJoinTask.java:289)
	at java.util.concurrent.ForkJoinPool$WorkQueue.runTask(ForkJoinPool.java:1056)
	at java.util.concurrent.ForkJoinPool.runWorker(ForkJoinPool.java:1692)
	at java.util.concurrent.ForkJoinWorkerThread.run(ForkJoinWorkerThread.java:157)

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bbakerman commented on June 13, 2024

@kaseyreed - the Try types returned from the batch loader are unpacked into either errors or data values.

From this exception stack trace I cant see it as being cause by an action of dataloader code. Can you expand the stack trace

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bbakerman commented on June 13, 2024

I am going to close this issue as no activity has been done on it

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deverant commented on June 13, 2024

Hey all, I know I am resurrecting a very old issue, but since I just stumbled upon this error I figured I'd leave a note for anyone else that gets caught by this.

The issue happens if you have configured your dataloader to not do batching. In this cases the load command actually returns type Try<T> response back to you. If you need a non-batching dataloader you just need to take that into account in your code.

For the developers: The issue is that for non-batching dataloaders the load command is executed directly here:

java-dataloader/src/main/java/org/dataloader/DataLoaderHelper.java

Lines 124 to 131 in 5805475

 CompletableFuture<V> future = new CompletableFuture<>(); 

 if (batchingEnabled) { 

 loaderQueue.add(new LoaderQueueEntry<>(key, future, loadContext)); 

 } else { 

 stats.incrementBatchLoadCountBy(1); 

 // immediate execution of batch function 

 future = invokeLoaderImmediately(key, loadContext); 

 }

. This bypasses the code that opens up the Try object, which only happens when dispatching the queue:

java-dataloader/src/main/java/org/dataloader/DataLoaderHelper.java

Lines 218 to 263 in 5805475

 private CompletableFuture<List<V>> dispatchQueueBatch(List<K> keys, List<Object> callContexts, List<CompletableFuture<V>> queuedFutures) { 

 stats.incrementBatchLoadCountBy(keys.size()); 

 CompletionStage<List<V>> batchLoad = invokeLoader(keys, callContexts); 

 return batchLoad 

 .toCompletableFuture() 

 .thenApply(values -> { 

 assertResultSize(keys, values); 

 List<K> clearCacheKeys = new ArrayList<>(); 

 for (int idx = 0; idx < queuedFutures.size(); idx++) { 

 Object value = values.get(idx); 

 CompletableFuture<V> future = queuedFutures.get(idx); 

 if (value instanceof Throwable) { 

 stats.incrementLoadErrorCount(); 

 future.completeExceptionally((Throwable) value); 

 clearCacheKeys.add(keys.get(idx)); 

 } else if (value instanceof Try) { 

 // we allow the batch loader to return a Try so we can better represent a computation 

 // that might have worked or not. 

 Try<V> tryValue = (Try<V>) value; 

 if (tryValue.isSuccess()) { 

 future.complete(tryValue.get()); 

 } else { 

 stats.incrementLoadErrorCount(); 

 future.completeExceptionally(tryValue.getThrowable()); 

 clearCacheKeys.add(keys.get(idx)); 

 } 

 } else { 

 V val = (V) value; 

 future.complete(val); 

 } 

 } 

 possiblyClearCacheEntriesOnExceptions(clearCacheKeys); 

 return values; 

 }).exceptionally(ex -> { 

 stats.incrementBatchLoadExceptionCount(); 

 for (int idx = 0; idx < queuedFutures.size(); idx++) { 

 K key = keys.get(idx); 

 CompletableFuture<V> future = queuedFutures.get(idx); 

 future.completeExceptionally(ex); 

 // clear any cached view of this key because they all failed 

 dataLoader.clear(key); 

 } 

 return emptyList(); 

 }); 

 }

I don't know if this is intended behavior or not so I just leave the comment for now. :) Thanks for all your work on graphql-java!

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Class Cast Exception when attempting to utilize Try<T> about java-dataloader HOT 5 CLOSED

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	CompletableFuture<V> future = new CompletableFuture<>();
	if (batchingEnabled) {
	loaderQueue.add(new LoaderQueueEntry<>(key, future, loadContext));
	} else {
	stats.incrementBatchLoadCountBy(1);
	// immediate execution of batch function
	future = invokeLoaderImmediately(key, loadContext);
	}

	private CompletableFuture<List<V>> dispatchQueueBatch(List<K> keys, List<Object> callContexts, List<CompletableFuture<V>> queuedFutures) {
	stats.incrementBatchLoadCountBy(keys.size());
	CompletionStage<List<V>> batchLoad = invokeLoader(keys, callContexts);
	return batchLoad
	.toCompletableFuture()
	.thenApply(values -> {
	assertResultSize(keys, values);

	List<K> clearCacheKeys = new ArrayList<>();
	for (int idx = 0; idx < queuedFutures.size(); idx++) {
	Object value = values.get(idx);
	CompletableFuture<V> future = queuedFutures.get(idx);
	if (value instanceof Throwable) {
	stats.incrementLoadErrorCount();
	future.completeExceptionally((Throwable) value);
	clearCacheKeys.add(keys.get(idx));
	} else if (value instanceof Try) {
	// we allow the batch loader to return a Try so we can better represent a computation
	// that might have worked or not.
	Try<V> tryValue = (Try<V>) value;
	if (tryValue.isSuccess()) {
	future.complete(tryValue.get());
	} else {
	stats.incrementLoadErrorCount();
	future.completeExceptionally(tryValue.getThrowable());
	clearCacheKeys.add(keys.get(idx));
	}
	} else {
	V val = (V) value;
	future.complete(val);
	}
	}
	possiblyClearCacheEntriesOnExceptions(clearCacheKeys);
	return values;
	}).exceptionally(ex -> {
	stats.incrementBatchLoadExceptionCount();
	for (int idx = 0; idx < queuedFutures.size(); idx++) {
	K key = keys.get(idx);
	CompletableFuture<V> future = queuedFutures.get(idx);
	future.completeExceptionally(ex);
	// clear any cached view of this key because they all failed
	dataLoader.clear(key);
	}
	return emptyList();
	});
	}