192 lines
7.2 KiB
HTML
192 lines
7.2 KiB
HTML
<!DOCTYPE html>
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<title>Strolch: Transactions</title>
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<a class="navbar-brand" href="index.html">Strolch</a>
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<ul class="nav navbar-nav">
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<li><a href="index.html">Overview</a></li>
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<li><a href="api.html">API</a></li>
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<li class="active"><a href="documentation.html">Documentation</a></li>
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<div class="container">
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<div class="page-header">
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<h1 class="page-title">Documentation: Transactions</h1>
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<p class="lead page-description">This page discusses Strolch Transactions.</p>
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</div>
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<div class="content">
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<p>Strolch Transactions play a central role in a Strolch agent. A transaction is opened for a realm, and grants
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access to the model of the agent. Transactions are implemented as a Java <code>try-with-resources</code> by
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implementing the <code>AutoCloseable</code> interface. This makes it trivial to understand the scope of a
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transaction. </p>
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<p>Transactions handle the following:</p>
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<ul>
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<li>Opening and closing database connections</li>
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<li>Releasing locks to strolch elements, if <code>tx.lock(StrolchRootElement)</code> or <code>tx.lock(Locator)</code>
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was called
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</li>
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<li>Performing Commands by executing them in the added order, and validating them first.</li>
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<li>Exception handling</li>
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<li>Auditing</li>
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<li>Updating observers</li>
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</ul>
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<p>When a transaction is opened, it is by default read-only, i.e. does not perform any commands when it is
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closed. Should the TX perform commands, then it is important to call <code>tx.commitOnClose()</code>, but
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only at the end of the work, so that exception handling can properly work if something goes wrong.</p>
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<p><code>StrolchTransaction</code> offers a myriad of methods:</p>
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<ul>
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<li>find element by its <code>Locator</code></li>
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<li>get methods for elements by type and id, or using a <code>StringParameter</code> or <code>StringListParameter</code>
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references
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</li>
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<li>methods to add, update or remove elements</li>
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<li>assert privilege access</li>
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<li>get a new element by its template</li>
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<li>check if an element exists by type and id</li>
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<li>get streams for elements</li>
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<li>add commands for execution</li>
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</ul>
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<p>Transactions are opened by accessing the realm, but there are convenience methods depending on the
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use-case:</p>
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<ul>
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<li>In Services: by calling one of the <code>openTx()</code>-methods</li>
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<li>In Commands: Transactions are already open, use method <code>tx()</code> to get instance. <b>Note:</b>
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don't open a new TX inside a TX for the same realm!
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</li>
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<li>REST API: <code>RestfulStrolchComponent.openTx()</code></li>
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</ul>
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<p>Important is to always open the transaction as a try-with-resource block and to define if the TX should
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commit, or not:</p>
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<pre>
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try (StrolchTransaction tx = openTx(...)) {
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// read lock our object
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Locator ferrariLoc = Resource.locatorFor("Car", "ferrari");
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tx.lock(ferrariLoc);
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// find a car by locator
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Resource ferrari = tx.findElement(ferrariLoc);
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// get a car by ID
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Resource opel = tx.getResourceBy("Car", "opel", true);
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// modify ball
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opel.setName("Opel Corsa");
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tx.update(opel);
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// get by string reference
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StringParameter ownerP = ferrari.getParameter("relations", "owner", true);
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Resource owner = tx.getResourceBy(ownerP, true);
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// get by string list reference
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StringListParameter previousOwnersP = opel.getParameter("relations", "previousOwners", true);
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List<Resource> previousOwners = tx.getResourcesBy(previousOwnersP, true);
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// check resource exists
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if (tx.hasResource("Car", "audi")) {
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Resource audi = tx.getResourceBy("Car", "audi", true);
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// assert has privilege to remove a car
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tx.assertHasPrivilege(Operation.REMOVE, audi);
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// remove the car
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tx.remove(audi);
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}
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// iterate all cars
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tx.streamResources("Car").forEach(car -> {
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logger.info("Car: " + car.getId());
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});
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// commit if TX was changed
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if (tx.needsCommit())
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tx.commitOnClose();
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}</pre>
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<p class="text-muted">© Strolch / <a href="mailto:eitch@eitchnet.ch">Robert von Burg</a> / Hosting by
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