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Thu Feb 10 21:02:37 2005 UTC (4 years, 9 months ago) by mvalenta
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Thu Feb 10 21:02:37 2005 UTC (4 years, 9 months ago) by mvalenta
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Wrote blurb on using ResourceMappings
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<title>Support Logical Resources: Resource Mappings</title>
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<td align="left" valign="top" bgcolor="#0080c0"> <b><font
color="#ffffff" face="Arial,Helvetica"> Eclipse 3.1 - Support Logical Resources
- Resource Mappings</font></b></td>
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<h1>Support Logical Resources - Resource Mappings</h1>
This document outlines the chosen solution to the adaptables problem outlined
in the <a href="logical-physical-public.html"><strong>Support Logical Resources</strong></a>
plan item problem description document. Feedback is strongly encouraged and may
be provided on the platform-team-dev mailing list or in the <a
href="http://bugs.eclipse.org/bugs/show_bug.cgi?id=37723">bug report</a> for
this plan item. The API described in this document is not yet final and may undergo
some revision before the end of the Eclipse 3.1 development cycle.
<h3>The Basic Resource Mapping API</h3>
<p>This solution involves adding API to the Resources plugin that maps logical
elements to physical ones. The API is purposely simple with logical model manipulations
omitted. A client can't use this interface to display logical models or gain
any interesting additional knowledge about it. The API consists of the following
classes: </p>
<ul>
<li><strong>ResourceMapping</strong>: class to which logical model elements
adapt to indicate that the model corresponds to a set of resources in the
workspace. The complete <code>ResourceMapping</code> class can be viewed <a href="http://dev.eclipse.org/viewcvs/index.cgi/org.eclipse.core.resources/src/org/eclipse/core/resources/mapping/ResourceMapping.java?rev=HEAD&content-type=text/vnd.viewcvs-markup">here</a>.
The methods of interest are:
<ul>
<li><code>Object getModelObject()</code>: The model object from which the
mapping was derived (or adapted).</li>
<li><code>ResourceTraversal[] getTraversals(ResourceMappingContext, IProgressMonitor)</code>:
The resource traversal that cover the resources that constitute the model
object.</li>
</ul>
</li>
<li><strong>ResourceTraversal</strong>: A <a href="http://dev.eclipse.org/viewcvs/index.cgi/org.eclipse.core.resources/src/org/eclipse/core/resources/mapping/ResourceTraversal.java?rev=HEAD&content-type=text/vnd.viewcvs-markup"><code>ResourceTraversal</code></a>
simply contains a set of resources and a depth flag that indicates the depth
to which the resources in the traversal are associated with the originating
model object. Resource traversals are provided to a client by a resource mapping
in order to describe the contents of a model in sich a way that a repository
provider can perform its operations in as efficient a means as possible.</li>
<li><strong>ResourceMappingContext</strong>: a context that is provided to the
resource mapping by the client. This context allows the logical model to determine
what the remote state of the model is so that the proper resources can be
covered by the resource traversals returned by the resource mapping. The use
of the<code> <a href="http://dev.eclipse.org/viewcvs/index.cgi/org.eclipse.core.resources/src/org/eclipse/core/resources/mapping/ResourceMappingContext.java?rev=HEAD&content-type=text/vnd.viewcvs-markup">ResourceMappingContext</a></code>
is a bit more complicated and is described <a href="#ResourceMappingContext">later</a>.</li>
</ul>
<p>There are two types of plugins that should be interested in resource mappings.
Those who provide a model that consists of or is persisted in resources in the
workspace and those that want to perform operations of resources. The following
two sections describe how to associate a resource mapping with a model object
and how to contribute menus to objects that adapt to resource mappings.</p>
<h4>Adapting a Model to a ResourceMapping</h4>
<p>Plugins that adapted their model objects to <code>IResource</code> in order
to get resource specific object contributions shown in the context menu can
now adapt to <code>ResourceMapping</code> if a richer description of how the
object adapts to resources is benefitial. However, they are not required to
do so if there is no benefit. For instance a Java class that now currently adapts
to <code>IFile</code> need no adapt to <code>ResourceMapping</code> since nothing
is gained. However, a Java package shoudl adapt to <code>ResourceMapping</code>
in order to indicate that the package is only the files in the corresponding
folder and not the subfolders.</p>
<p>An adapter factory can be used to adapt model objects into resource mappings.
The following is the XML markup for contributing an adapter factory in a plugin
manifest. </p>
<pre style="background-color: rgb(204, 204, 255);"> <extension<br> point="org.eclipse.core.runtime.adapters"><br> <factory<br> class="org.eclipse.example.library.logical.AdapterFactory"<br> adaptableType="org.eclipse.example.library.Book"><br> <adapter type="org.eclipse.core.resources.mapping.ResourceMapping"/><br> </factory><br> <factory<br> class="org.eclipse.example.library.logical.AdapterFactory"<br> adaptableType="org.eclipse.example.library.Library"><br> <adapter type="org.eclipse.core.resources.mapping.ResourceMapping"/><br> </factory><br> ...<br> </extension></pre>
<p>For popup menu contribuions, it is not required that the model objects implement
the <code>IAdaptable</code> interface. However, if they do they must ensure
that the Platform adapter manager is consulted. This can be done by either subclassing
<code>PlatformObject</code> or by using the following line of code:</p>
<blockquote>
<p><code>Platform.getAdapterManager().getAdapter(Object, Class)</code></p>
</blockquote>
<p>The above is the preferrable approach. However, the model object can implement
the IAdaptable interface and provide a <code>getAdapter(Class)</code> implementation
that creates returns an instance of <code>ResourceMapping</code> explicitly
when asked for one. This is a more straightforward approach but the least desirable
as the model must have explicit knowledge of the adaptation to resources.</p>
<h4>Contributing Menus to Resource Mappings</h4>
<p>Plug-ins that contribute extensions to adaptable extension points will have
to make two changes to support the new <code>ResourceMapping</code> APIs:</p>
<ol>
<li>Update their plugin.xml files tochange the objectClass of their adaptable
contributions to <code>ResourceMapping</code> (for those for which this is
appropriate).</li>
<li>Update their actions to work on <code>ResourceMapping</code> instead of
IResource and respect the depth constraints provided in the traversals.</li>
<li>(Optional) provide a <code>ResourceMappingContext</code> if they manage
remote resources (more on this <a href="#ResourceMappingContext">below</a>)</li>
</ol>
<p>First of all, plugins that add object contributions to <code>IResource</code>
(CVS, Search, Compare) can now add them to <code>ResourceMapping</code> instead,
if the action can apply to multiple resources. Here is an XML snipet:</p>
<pre style="background-color: rgb(204, 204, 255);"> <extension<br> point="org.eclipse.ui.popupMenus"><br> <objectContribution<br> adaptable="true"<br> objectClass="org.eclipse.core.resources.mapping.ResourceMapping"<br> id="org.eclipse.example.library.ResourceMappingContributions"><br> <action<br> label="Show Resource Mappings"<br> class="org.eclipse.example.library.contributions.ShowResourceMappingsAction"<br> menubarPath="additions"<br> id="org.eclipse.example.library.showMappings"/> <br> </objectContribution><br> </extension></pre>
<p>Contributions to <code>ResourceMapping</code> will automatically apply to objects
that adapt to <code>IResource</code>. This transitive association is handled
by the Workbench.</p>
<p>Filtering of the contributions to resource mappings can be done using action
filters or expressions although expressions are perferrable. An expression for
filtering by project persistant property has been added to allow repository
providers to have their menus appear on projects that are mapped to their repositories.</p>
<pre style="background-color: rgb(204, 204, 255);"> <extension<br> point="org.eclipse.ui.popupMenus"><br> <objectContribution<br> objectClass="org.eclipse.core.resources.mapping.ResourceMapping"<br> adaptable="true"<br> id="org.eclipse.team.ccvs.ui.ResourceMapperContributions"><br> <enablement><br> <adapt type="org.eclipse.core.resources.mapping.ResourceMapping"><br> <test
property="org.eclipse.ui.ide.projectPersistentProperty"
args="org.eclipse.team.core.repository=org.eclipse.team.cvs.core.cvsnature" /><br> </adapt><br> </enablement><br> <action<br> label="%UpdateAction.label"<br> definitionId="org.eclipse.team.cvs.ui.update"<br> class="org.eclipse.team.internal.ccvs.ui.actions.UpdateAction"<br> tooltip="%UpdateAction.tooltip"<br> menubarPath="team.main/group2"<br> id="org.eclipse.team.cvs.ui.update"><br> </action>
...<br> </objectContribution><br> </extension></pre>
<p>Actions that have been contributed to the <code>ResourceMapping</code> class
will be given a selection that contains one or more <code>ResourceMappings</code>.
It is the actions responsibility to translate the resource mapping into a set
of resources to be operated on. This can be done by calling <code>getTraversals</code>
to get the traversals of the mapping. Traversals are used to allow the clients
of the traversal to optimize their operations based on the depth of the resources
being traversed. A client may traverse the resource manually or may use the
resource and the depth as input into an operation that the action delegates
to do the work. As an example, if the user performs a CVS update on a java package
and the java package resource mapping maps to a folder of depth one, CVS would
issue an appropriat command ("cvs update -l" for those who are curious)
which would perform a shallow update on the folder the pakcage represents.</p>
<h3><a name="ResourceMappingContext"></a>Resource Mapping Context</h3>
<p>One of the advantages of a Resouce Mapping API is that it allows plug-ins to
implement any operations they desire in terms of resource mappings (e.g. CVS
update, CVS commit, CVS tag, dirty decoration, etc.). However, the API that
has been introduced so far deals only with the local state of the model. When
working with a model that may be shared between developers, you end up in a
situation where the remote state of the model (i.e. the state of the model that
another user has checked-in to the repository) may differ from the state in
the workspace. If you performed a CVS update, you would want the local state
of the model to match the remote state even if it meant that additional files
needed to be included or some files needed to be removed.</p>
<p>This is not an issue for some logical models. For instance, a java package
is a container visited to a depth of one, regardless of the remote state of
the model. Given this, a repository provider can easily determine that outgoing
deletions should be included when committing or that incoming additions should
be included when updating. However, the resources that constitute some logical
models may change over time. For instance, the resources that constitute a model
element may depend of the contents of a manifest file (or some other similar
mechanism). In order for the ResourceMapping to return the proper traversal,
it must access the remote contents of the manifest file (if it differes from
the local contents) in order to see if there are additional resources that need
to be included. These additional resources may not exist in the workspace but
the repository provider would know how to make sure they did when the selected
action was performed.</p>
<p>In order to support these more complex models, a <code>ResourceMappingContext</code>
can be passed to the <code>ResourceMapping#getTraversals</code> method. When
a context is provided, the mapping can use it to ensure that all the necessary
resources are included in the traversal. If a context is not provided, the mapping
can assume that only the local state is of interest. </p>
<h4>When does a ResourceMapping need to worry about the ResourceMappingContext?</h4>
<p>A <code>ResourceMapping</code> need only worry about a context supplied to
the <code>getTraversals</code> method in cases were the resources that make
up a model change over time and the relationship between the model and resources
cannot be described by a simple traversal that is gauranteed to encompass those
resources (and only those resources) that consitute the model. For example,
although the resources of a Java package may change over time, the package can
be described as a folder of depth one so a resource mapping for java packages
would not ned to make use of the resource mapping context. </p>
<p>As a more complicated example, consider an HTML file that contains several
images. Let's mak the assumption that any images references from an HTML file
ae part of the model of that file. When updating the local contents of the HTML
file from a repository, the user would expect that any new images would be included.
The getTraversals method for a ResourceMapping for the HTML file model would
look something like this:</p>
<pre style="background-color: rgb(204, 204, 255);">public class HTNLResourceMapping extends ResourceMapping {
private HTMLFile htmlFile;
getTraversals(ResourceMappingContext context, IPorgressMonitor monitor) {
IResource[] resources = htmlFile.getRsources();
if (context != null) {
// Look for any additional resources on the server
IFile file = htmlFile.getFile();
if (context.contentDiffers(file, monitor) {
IStorage storage = context.fetchContents(file, monitor);
IResource[] additionalResources = getReferences(storage.getContents());
resources = combine(resources, additionalResources);
}
}
return new ResourceTraversal(resources, IResource.DEPTH_ZERO);
}<br>}</pre>
<h4>When does a client need to provide a ResourceMappingContext?</h4>
<p>Any client that is providing the ability of sharing workspace resources through
a repository and is supporting ResourceMappings should provide an appropriate
context for determining the relevant remote state o the model resources. The
context provides three basic quieries:</p>
<ul>
<li>Does the local contents differ from the remote contents</li>
<li>What are the remote contents of a file</li>
<li>What are the remote memebers of a folder</li>
</ul>
<p>The answer to the first question above depends on the type of operation that
is being performed:</p>
<ul>
<li>When checking in a resource, the context would consider that a file's contents
differ if the local contents have been modified since the last check-in.</li>
<li>When updating a resource, the context would consider that a file's contents
differ if the remote contents have been modified since the users last update.</li>
<li>When replacing a resource, the context would consider that a file's contents
differ if either the the local or remote contents have changed since the last
synchronization.</li>
</ul>
<p>The Eclipse Team API includes a <code>Subcriber</code> class that defines an
API for providing the synchronization state between the local workspace and
a remote server. A <code>SubscriberResourceMappingContext</code> has been created
that uses a <code>Subscriber</code> to access the necessary remote state. Clients
that have a <code>Subscriber</code> do not need to do any additional work to
get a resource mapping context.</p>
<h2>How this will affect existing plug-ins</h2>
<p>Existing plugins do not need to change at all unless they want to take advantage
of the new API. For plugins that provide logical modes, it may be worthwhile
for them to adapt their model objects to <code>ResourceMappings</code>. Of course,
this is only a benefit when combined with a repository provider implementation
that contributes at last some of it's actions to resource mappings.</p>
<span style="font-weight: bold;"></span>
<h2>Open Issues</h2>
<p>The following issues would need to be addressed for this solutions.</p>
<ul>
<li> Plugins that add object contributions will have to modify their actions
to handle logical resources. There should be some standard UI components for
showing the mappings. For instance you could show the logical model at the
top and in a details part the physical files/folders that will be affected
by the operation.</li>
<li>Would it be possible to add a workbench adapter to specific implementations
IModelElement in order to get an image and label for a model element?</li>
<li>Can the user benefit from resource mappings in cases where the repository
provider isn't mapping aware?<br>
</li>
</ul>
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