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[[library-uowfile,UoWFile Library]]
= UoWFile =

[devstatus]
--------------
source=libraries/uowfile/dev-status.xml
--------------

The UoWFile Library provides an easy way to bind file operations to UnitOfWorks.

In other words, using this library you can easily attach files to your
Composites, mostly EntityComposites, so that if the UoW gets discarded, changes
to files are discarded too. Concurrent modifications are properly handled.

Note that it has a performance impact relative to the files size as it
duplicates the file to keep a backup for eventual rollback. However, the API
provides a way to get non-managed handles on the attached files to keep your
read-only operations fast.

The location of files is left to the developer using a private mixin.


include::../../build/docs/buildinfo/artifact.txt[]

== Logging ==

The SLF4J Logger used by this library is named "org.qi4j.library.uowfile".


== Add an attached file to an Entity ==

Let's say you have the following Entity:

[snippet,java]
----
source=libraries/uowfile/src/test/java/org/qi4j/library/uowfile/HasUoWFileTest.java
tag=entity
----

To add an attached file to it you first need to extends HasUoWFileLifecycle:

[snippet,java]
----
source=libraries/uowfile/src/test/java/org/qi4j/library/uowfile/HasUoWFileTest.java
tag=uowfile
----

This provides you with the following contract:

[snippet,java]
----
source=libraries/uowfile/src/main/java/org/qi4j/library/uowfile/singular/HasUoWFile.java
tag=contract
----

Next you need to write the UoWFileLocator mixin:

[snippet,java]
----
source=libraries/uowfile/src/test/java/org/qi4j/library/uowfile/HasUoWFileTest.java
tag=locator
----

Assemble all this as follow:

[snippet,java]
----
source=libraries/uowfile/src/test/java/org/qi4j/library/uowfile/HasUoWFileTest.java
tag=assembly
----

You can now use the following methods on your EntityComposite:

[snippet,java]
----
source=libraries/uowfile/src/test/java/org/qi4j/library/uowfile/HasUoWFileTest.java
tag=api
----


== Going plural ==

Now if you want to attach several files to one entity, this library provides a
simple mechanism allowing you to use any enum as discriminator.

Let's say you have the following Entity:

[snippet,java]
----
source=libraries/uowfile/src/test/java/org/qi4j/library/uowfile/HasUoWFilesTest.java
tag=entity
----

It's the very same as the one used to start the singular file support described
above.

To add an attached file to it you first need to write an enum and extends
HasUoWFilesLifecycle:

[snippet,java]
----
source=libraries/uowfile/src/test/java/org/qi4j/library/uowfile/HasUoWFilesTest.java
tag=uowfile
----

This provides you with the following contract:

[snippet,java]
----
source=libraries/uowfile/src/main/java/org/qi4j/library/uowfile/plural/HasUoWFiles.java
tag=contract
----

Next you need to write the UoWFileLocator mixin:

[snippet,java]
----
source=libraries/uowfile/src/test/java/org/qi4j/library/uowfile/HasUoWFilesTest.java
tag=locator
----

Assemble all this as follow:

[snippet,java]
----
source=libraries/uowfile/src/test/java/org/qi4j/library/uowfile/HasUoWFilesTest.java
tag=assembly
----

You can now use the following methods on your EntityComposite:

[snippet,java]
----
source=libraries/uowfile/src/test/java/org/qi4j/library/uowfile/HasUoWFilesTest.java
tag=api
----