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<a class="user-hover" rel="emmanuel" id="email_emmanuel" href="https://hibernate.onjira.com/secure/ViewProfile.jspa?name=emmanuel" style="color:#6c797f;">Emmanuel Bernard</a>
commented on <img src="https://hibernate.onjira.com/images/icons/bug.gif" height="16" width="16" border="0" align="absmiddle" alt="Bug"> <a style='color:#6c797f;text-decoration:none;' href='https://hibernate.onjira.com/browse/OGM-208'>OGM-208</a>
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<a style='color:#6c797f;text-decoration:none;' href='https://hibernate.onjira.com/browse/OGM-208'><strong>Create facility for OGM core and Dialects to receive custom metadata (annotation, programmatic) associated to entities, properties or associations</strong></a>
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<div class="comment-block" style="background-color:#edf5ff;border:1px solid #dddddd;color:#000000;padding:12px;"><h2><a name="Internalmodel"></a>Internal model</h2>
<p>The internal model can be type-safe or not.<br/>
We need a way to identify an option from another.</p>
<p>Each option needs a uniquely identifying key object.<br/>
This will tell if an option is overridden by another context<br/>
or merely duplicated by other values.</p>
<p>For example a named query using different names are not overlapping<br/>
but a named query with the same name is replaced by a more specific context.</p>
<div class="code panel" style="border-width: 1px;"><div class="codeContent panelContent">
<pre class="code-java">/**
* Interface required to be returned by the generator classes
* It represents a tuple of the option and the value associated
*
* Option can be of any type, in particular it could be represented as
*
* - an <span class="code-keyword">enum</span> value
* - a <span class="code-object">Class</span> object in particular an annotation class object
* - a <span class="code-object">String</span>
*
* What is important is that the Option is unique according to
* the `equals()` operation amongst the realm of possible options.
*
* Likewise, Value can be of any type.
*/
<span class="code-keyword">public</span> <span class="code-keyword">interface</span> OptionValueTuple<Option,Value> {
Option getOption();
Value getValue();
}
<span class="code-comment">// most likely an anonymous class in a generator implementation
</span> <span class="code-keyword">public</span> class QuorumOptionValueTuple <span class="code-keyword">implements</span> OptionValueTuple<OptionEnum,Quorum> {
<span class="code-keyword">private</span> <span class="code-keyword">final</span> <span class="code-object">int</span> read;
<span class="code-keyword">private</span> <span class="code-keyword">final</span> <span class="code-object">int</span> write;
<span class="code-keyword">public</span> QuorumOptionValueTuple(<span class="code-object">int</span> read, <span class="code-object">int</span> write) { <span class="code-keyword">this</span>.read = read; <span class="code-keyword">this</span>.write = write; }
<span class="code-keyword">public</span> OptionEnum getOption() { <span class="code-keyword">return</span> OptionEnum.QUORUM; }
<span class="code-keyword">public</span> Quorum getValue() { <span class="code-keyword">return</span> <span class="code-keyword">new</span> Quorum(read, write); }
}
<span class="code-comment">//an example of possible Option identifier
</span> <span class="code-keyword">public</span> <span class="code-keyword">enum</span> OptionEnum {
QUORUM;
}
<span class="code-comment">// the object model representing the QUORUM value
</span> <span class="code-keyword">public</span> class Quorum {
<span class="code-keyword">private</span> <span class="code-keyword">final</span> <span class="code-object">int</span> read;
<span class="code-keyword">private</span> <span class="code-keyword">final</span> <span class="code-object">int</span> write;
<span class="code-keyword">public</span> Quorum(<span class="code-object">int</span> read, <span class="code-object">int</span> write) { <span class="code-keyword">this</span>.read = read; <span class="code-keyword">this</span>.write = write }
}</pre>
</div></div>
<p>`OptionValueTuple` will be used by Hibernate OGM to collect a map of option / option value and expose that to <br/>
the `GridDialect`.</p>
<p>Problem, there is a notion of Option <b>Type</b> and a unique identifier made of option type and some other unique<br/>
identifier like in a named query. We uniquely define a named query by it's NamedQuery type and its actual name.</p>
<p>The Option object could be a subtype of `MultiOption`</p>
<div class="code panel" style="border-width: 1px;"><div class="codeContent panelContent">
<pre class="code-java">/**
* Common <span class="code-keyword">interface</span> <span class="code-keyword">for</span> options that can receive multiple values
* like named queries.
* TODO: are generics useful?
*/
<span class="code-keyword">public</span> class MultiOption<Type,Id> {
/**
* <span class="code-object">Class</span> of option, <span class="code-keyword">this</span> type can be any type but typically is an
* <span class="code-keyword">enum</span>, a <span class="code-object">Class</span> instance or a <span class="code-object">String</span>.
*/
<span class="code-keyword">abstract</span> Type getType();
/**
* Uniquely identify an option <span class="code-keyword">for</span> a given type
*/
<span class="code-keyword">abstract</span> Id getUniqueIdentifier();
<span class="code-keyword">public</span> <span class="code-object">boolean</span> equals(<span class="code-object">Object</span> that) {
<span class="code-comment">//TODO implementation using getType and getUniqueIdentifier
</span> }
<span class="code-keyword">public</span> <span class="code-object">int</span> hashCode() {
<span class="code-comment">//TODO implementation using getType and getUniqueIdentifier
</span> }
}
/**
* Example of implementation
*/
<span class="code-keyword">public</span> NamedQueryOption <span class="code-keyword">extends</span> MultiOption<<span class="code-object">Class</span><?>,<span class="code-object">String</span>> {
<span class="code-keyword">private</span> <span class="code-keyword">final</span> <span class="code-object">String</span> queryName;
<span class="code-keyword">public</span> NamedQueryOption(<span class="code-object">String</span> queryName) { <span class="code-keyword">this</span>.queryName = queryName; }
<span class="code-object">Class</span><?> getType() { <span class="code-keyword">return</span> NamedQuery.class; }
<span class="code-object">String</span> getUniqueIdentifier() { <span class="code-keyword">return</span> queryName; }
}
<span class="code-keyword">public</span> class NamedQuery {
<span class="code-keyword">private</span> <span class="code-object">String</span> name;
<span class="code-keyword">private</span> <span class="code-object">String</span> hql;
...
}
<span class="code-comment">// most likely an anonymous class in a generator implementation
</span> <span class="code-keyword">public</span> class NamedQueryOptionValueTuple <span class="code-keyword">implements</span> OptionValueTuple<NamedQueryOption, NamedQuery> {
<span class="code-keyword">public</span> NamedQueryOptionValueTuple(<span class="code-object">String</span> name, <span class="code-object">String</span> hsql) { ... }
<span class="code-keyword">public</span> NamedQueryOption getOption() { <span class="code-keyword">return</span> <span class="code-keyword">new</span> NamedQueryOption(name); }
<span class="code-keyword">public</span> NamedQuery getValue() { <span class="code-keyword">return</span> <span class="code-keyword">new</span> NamedQuery(name, hql);
}</pre>
</div></div>
<p>We could offer the ability to filter options by option or option type to help navigate them.<br/>
Wrt overriding, an option is overridden by a closer scope. Same for an option type with the same<br/>
unique identifier.</p>
<h3><a name="UsagefromaGridDialect"></a>Usage from a GridDialect</h3>
<p>We could imagine the following usage</p>
<div class="code panel" style="border-width: 1px;"><div class="codeContent panelContent">
<pre class="code-java">Quorum quorum = (Quorum) context.inGlobalContext().getOption( QUORUM );
List<NamedQuery> queries = (List<NamedQuery>) context.inEntityContext().getOptionByType(NamedQuery.class);</pre>
</div></div>
<h3><a name="Observations"></a>Observations</h3>
<p>It seems the model is fairly verbose and I am willing to simplify it if we can. I am especially concerned<br/>
about the amount of concepts and classes the designer of an option needs to provide.</p>
<p>Paradoxically, there is not type-safe link between an option and its value besides the `OptionValueTuple`<br/>
which is not meant to be used by consumers of options. The `GridDialect` is force to downcast the data<br/>
which is not ideal.</p>
<p>I am also concerned about the fact that the set of options is quite dispersed due:</p>
<ul class="alternate" type="square">
<li>the ability to define the option (or option type) type freely</li>
<li>the fact that some options are specific to a given datastore provider</li>
</ul>
<p>The design seems to need refinement but I have been working on it for some time now and need a fresh look at it.</p></div>
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