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--- tutorial:transfer-api_storage [2021/10/30 09:37] – technici4n
+++ tutorial:transfer-api_storage [2021/10/30 10:25] (current) – external edit 127.0.0.1
@@ Line 1: / Line 1: @@
-===== Fabric Transfer API: Understanding Storage<T> =====
+===== Fabric Transfer API: Understanding Storage<FluidVariant> =====
 //This article is part of a series on the Fabric Transfer API. [[tutorial:transfer-api|Link to the home page of the series]].//
@@ Line 27: / Line 27: @@
 </code>
-==== What you can do with a Storage<FluidVariant> ====
+==== A look at Storage<T> ====
 Let's have a look at ''Storage.java'':
 <code java>
 public interface Storage<T> {
-	// Insert a resource in the storage.
+	// Try to insert a resource in the storage, return how much was inserted.
 	long insert(T resource, long maxAmount, TransactionContext transaction);
-	// Extract a resource from the storage.
+	// Try to extract a resource from the storage, return how much was extracted.
 	long extract(T resource, long maxAmount, TransactionContext transaction);
 	// Iterate over the contents of this storage.
@@ Line 39: / Line 39: @@
 	...
+}
 </code>
+This interface allows us to insert into a storage, extract from it, and read its contents.
+==== First example: how to insert exactly one bucket of water into a storage ====
+<code java>
+Storage<FluidVariant> storage = ...;
+FluidVariant water = FluidVariant.of(Fluids.WATER);
+// Open a transaction: this allows cancelling the operation if it doesn't go as expected.
+try (Transaction transaction = Transaction.openOuter()) {
+	// Try to insert, will return how much was actually inserted.
+	long amountInserted = storage.insert(water, FluidConstants.BUCKET, transaction);
+	if (amountInserted == FluidConstants.BUCKET) {
+		// "Commit" the transaction: this validates all the operations that were part of this transaction.
+		// You should call this if you are satisfied with the result of the operation, and want to keep it.
+		transaction.commit();
+	} else {
+		// Doing nothing "aborts" the transaction: this cancels the insertion.
+		// You should call this if you are not satisfied with the result of the operation, and want to abort it.
+	}
+}
+</code>
+==== Second example: move exactly one bucket of lava from a storage to another storage ====
+<code java>
+import static net.fabricmc.fabric.api.transfer.v1.fluid.FluidConstants.BUCKET; // a bit shorter to type :)
+Storage<FluidVariant> source, destination;
+FluidVariant lava = FluidVariant.of(Fluids.LAVA);
+try (Transaction transaction = Transaction.openOuter()) {
+	if (source.extract(lava, BUCKET, transaction) == BUCKET && destination.insert(lava, BUCKET, transaction) == BUCKET) {
+		transaction.commit();
+	}
+}
+</code>
+Hopefully you understand why this works, and why this will never duplicate or void fluid.
+==== A more complicated example: Extracting the contents of a storage ====
+In the previous example, we knew that we wanted to move water or lava. But what if we don't know what to extract? The answer is: iterate over the contents!
+This example also introduces the concept of nested transactions.
+<code java>
+Storage<FluidVariant> storage;
+Predicate<FluidVariant> filter = fv -> fv.isOf(Fluids.WATER); // What we want to extract, in this example let's say we want to extract any water, regardless of its NBT tag.
+long totalExtracted = 0;
+// Open a transaction, as before.
+try (Transaction transaction = Transaction.openOuter()) {
+	// Loop over the contents! Each StorageView<T> can contain at most one resource. You can think of a StorageView as an inventory slot.
+	for (StorageView<FluidVariant> view : storage.iterable(transaction)) {
+		if (view.isResourceBlank()) continue; // This means that the view contains no resource, represented by FluidVariant.blank().
+		FluidVariant storedResource = view.getResource(); // Current resource
+		if (!filter.test(storedResource)) continue; // The filter rejected this resource, skip it.
+		// If you want to extract any amount <= view.getAmount(), do this.
+		totalExtracted += view.extract(storedResource, view.getAmount(), transaction);
+		// If you want to extract either the exact amount or nothing, you can use a nested transaction!
+		try (Transaction nestedTransaction = transaction.openNested()) {
+			long amount = view.getAmount(); // The amount will change after the call to extract, so make sure to save it first.
+			long extracted = view.extract(storedResource, amount, nestedTransaction);
+			if (extracted == amount) {
+				totalExtracted += amount;
+				nestedTransaction.commit(); // Validate the nestedTransaction: the outer one will have to committed as well to validate this change.
+			} else {
+				// If we do nothing, the extraction is cancelled immediately when nestedTransaction is closed at the end of the try { ... } block.
+			}
+		}
+	}
+	transaction.commit(); // Don't forget to commit, or all of the extraction will be cancelled!
+}
+</code>
+==== Conclusion ====
+You should now be able to use ''Storage''s and ''StorageView''s. They can be a bit challenging in the beginning, but once you're used to them they are very easy to work with.
+You should also have a look at ''StorageUtil'': it already contains functions that perform common transfer operations. In particular, [[https://maven.fabricmc.net/docs/fabric-api-0.41.0+1.17/net/fabricmc/fabric/api/transfer/v1/storage/StorageUtil.html#move(net.fabricmc.fabric.api.transfer.v1.storage.Storage,net.fabricmc.fabric.api.transfer.v1.storage.Storage,java.util.function.Predicate,long,net.fabricmc.fabric.api.transfer.v1.transaction.TransactionContext)|move]] is very useful if you just want to move resources between two storages.