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<h1 class="page-title">Documentation: Realms</h1>
<p class="lead page-description">This page discusses Strolch Realms</p>
</div>
<div class="content">
<p>Realms implement multi-tenant capabilities. A Strolch agent can have an arbitrary number of realms configured
and each realm has its own persistence configuration, allowing to separate mandates completely.</p>
A realm can run in one of the following modes:
<ul>
<li>EMPTY <br /> This is a transient data store mode, where no model changes are persisted - they are only
kept in memory. When the Strolch agent is started, this realm is empty as no data is loaded.
</li>
<li>TRANSIENT <br /> This is the same as EMPTY, but with the difference that when the Strolch agent is
started, a model file is parsed and the in-memory realm is populated with the elements parsed from the
model file.
</li>
<li>CACHED <br /> In this mode, all data is stored in-memory, and any changes made are written back to the
persistence layer. This allows for fast in-memory qeuries, but makes sure no data is lost when the agent
is restarted.
</li>
</ul>
<p>Realms are mostly hidden from a developer as a <code>StrolchTransaction</code> exposes all important
operations needed to access Strolch objects. A developer will however need to configure the realms for their
specific project. If the project only requires one realm, then the <code>defaultRealm</code> can be used,
where the developer only is required to configure the mode and any relevant model file.</p>
<p>If the mode is CACHED, then the <code>PersistenceHandler</code> component is required to be configured, so
that the DAOs know how to access the underlying database.</p>
<p>The configuration in the <code>StrolchConfiguration.xml</code> file is as follows:</p>
<pre>
&lt;StrolchConfiguration&gt;
&lt;env id="dev"&gt;
...
&lt;Component&gt;
&lt;name&gt;RealmHandler&lt;/name&gt;
&lt;api&gt;li.strolch.agent.api.RealmHandler&lt;/api&gt;
&lt;impl&gt;li.strolch.agent.impl.DefaultRealmHandler&lt;/impl&gt;
&lt;depends&gt;PrivilegeHandler&lt;/depends&gt;
&lt;!-- if CACHED: --&gt;
&lt;!--depends&gt;PersistenceHandler&lt;/depends--&gt;
&lt;Properties&gt;
&lt;dataStoreMode&gt;EMPTY|TRANSIENT|CACHED&lt;/dataStoreMode&gt;
&lt;dataStoreFile&gt;StrolchModel.xml&lt;/dataStoreFile&gt;
&lt;/Properties&gt;
&lt;/Component&gt;
...
&lt;/env&gt;
&lt;/StrolchConfiguration&gt;
</pre>
<p>A multi-realm configuration would be as follows. Note how the <code>defaultRealm</code> is still enabled, and
has its configuration as before. Further the PostgreSQL <code>PersistenceHandler</code> is configured to show
how the realms are connected to the persistence handler:</p>
<pre>
&lt;StrolchConfiguration&gt;
&lt;env id="dev"&gt;
...
&lt;Component&gt;
&lt;name&gt;RealmHandler&lt;/name&gt;
&lt;api&gt;li.strolch.agent.api.RealmHandler&lt;/api&gt;
&lt;impl&gt;li.strolch.agent.impl.DefaultRealmHandler&lt;/impl&gt;
&lt;depends&gt;PrivilegeHandler&lt;/depends&gt;
&lt;depends&gt;PersistenceHandler&lt;/depends&gt;
&lt;Properties&gt;
&lt;realms&gt;defaultRealm, cachedRealm&lt;/realms&gt;
&lt;dataStoreMode&gt;TRANSIENT&lt;/dataStoreMode&gt;
&lt;dataStoreFile&gt;DefaultRealm.xml&lt;/dataStoreFile&gt;
&lt;dataStoreMode.cachedRealm&gt;CACHED&lt;/dataStoreMode.cachedRealm&gt;
&lt;dataStoreMode.emptyRealm&gt;EMPTY&lt;/dataStoreMode.emptyRealm&gt;
&lt;/Properties&gt;
&lt;/Component&gt;
&lt;Component&gt;
&lt;name&gt;PersistenceHandler&lt;/name&gt;
&lt;api&gt;li.strolch.persistence.api.PersistenceHandler&lt;/api&gt;
&lt;impl&gt;li.strolch.persistence.postgresql.PostgreSqlPersistenceHandler&lt;/impl&gt;
&lt;Properties&gt;
&lt;allowSchemaCreation&gt;true&lt;/allowSchemaCreation&gt;
&lt;allowSchemaDrop&gt;true&lt;/allowSchemaDrop&gt;
&lt;db.url.cachedRealm&gt;jdbc:postgresql://localhost/testdb2&lt;/db.url.cachedRealm&gt;
&lt;db.username.cachedRealm&gt;testuser2&lt;/db.username.cachedRealm&gt;
&lt;db.password.cachedRealm&gt;test&lt;/db.password.cachedRealm&gt;
&lt;db.pool.maximumPoolSize.cachedRealm&gt;1&lt;/db.pool.maximumPoolSize.cachedRealm&gt;
&lt;/Properties&gt;
&lt;/Component&gt;
...
&lt;/env&gt;
&lt;/StrolchConfiguration&gt;
</pre>
<p>Accessing a realm is done in multiple ways. Important is to note, that a user should use the <code>StrolchTransaction</code>
object, instead of accessing the Realm directly.</p>
<p>Opening a transaction is done from a <code>Service</code> by calling one of the <code>openTx()</code>-methods.
Nevertheless, the realm can be accessed as follows:</p>
<pre>
ComponentContainer container = getAgent().getContainer();
StrolchRealm realm = container.getRealm(StrolchConstants.DEFAULT_REALM);
try(StrolchTransaction tx = realm.openTx()) {
Resource resource = tx.getResourceBy("TestType", "MyTestResource");
...
}
</pre>
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