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<h1 class="text-4xl font-bold mb-4">Triggers & Events</h1>
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Define database triggers, event schedulers, and change streams for automated data handling.
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<h2 class="text-2xl font-semibold mb-4">Overview</h2>
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Triggers automatically execute code in response to database events like INSERT, UPDATE, and DELETE.
Prax provides a unified API for defining triggers across all supported databases.
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<th class="text-left py-3 px-4 font-semibold">Feature</th>
<th class="text-left py-3 px-4 font-semibold">PostgreSQL</th>
<th class="text-left py-3 px-4 font-semibold">MySQL</th>
<th class="text-left py-3 px-4 font-semibold">SQLite</th>
<th class="text-left py-3 px-4 font-semibold">MSSQL</th>
<th class="text-left py-3 px-4 font-semibold">MongoDB</th>
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<td class="py-3 px-4">Row-Level Triggers</td>
<td class="py-3 px-4"><span class="text-success-400">✅</span></td>
<td class="py-3 px-4"><span class="text-success-400">✅</span></td>
<td class="py-3 px-4"><span class="text-success-400">✅</span></td>
<td class="py-3 px-4"><span class="text-success-400">✅</span></td>
<td class="py-3 px-4"><span class="text-success-400">✅</span> Change Streams</td>
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<td class="py-3 px-4">Statement-Level</td>
<td class="py-3 px-4"><span class="text-success-400">✅</span></td>
<td class="py-3 px-4"><span class="text-muted">❌</span></td>
<td class="py-3 px-4"><span class="text-muted">❌</span></td>
<td class="py-3 px-4"><span class="text-success-400">✅</span></td>
<td class="py-3 px-4"><span class="text-muted">❌</span></td>
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<td class="py-3 px-4">INSTEAD OF</td>
<td class="py-3 px-4"><span class="text-success-400">✅</span></td>
<td class="py-3 px-4"><span class="text-muted">❌</span></td>
<td class="py-3 px-4"><span class="text-success-400">✅</span></td>
<td class="py-3 px-4"><span class="text-success-400">✅</span></td>
<td class="py-3 px-4"><span class="text-muted">❌</span></td>
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<td class="py-3 px-4">Event Scheduler</td>
<td class="py-3 px-4"><span class="text-muted">❌</span></td>
<td class="py-3 px-4"><span class="text-success-400">✅</span></td>
<td class="py-3 px-4"><span class="text-muted">❌</span></td>
<td class="py-3 px-4"><span class="text-success-400">✅</span> SQL Agent</td>
<td class="py-3 px-4"><span class="text-success-400">✅</span> Atlas Triggers</td>
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<h2 class="text-2xl font-semibold mb-4">Creating Triggers</h2>
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Use the <code class="px-2 py-1 bg-surface-elevated rounded">Trigger::builder()</code> API to create triggers.
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<app-code-block [code]="basicTrigger" language="rust" filename="src/triggers.rs" />
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<h2 class="text-2xl font-semibold mb-4">Conditional Triggers</h2>
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Add conditions to fire triggers only when specific criteria are met.
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<app-code-block [code]="conditionalTrigger" language="rust" filename="src/triggers.rs" />
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<h2 class="text-2xl font-semibold mb-4">INSTEAD OF Triggers</h2>
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Replace the default action for views, enabling them to be updatable.
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<app-code-block [code]="insteadOfTrigger" language="rust" filename="src/triggers.rs" />
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<h2 class="text-2xl font-semibold mb-4">Built-in Patterns</h2>
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Common trigger patterns are available out of the box.
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<app-code-block [code]="triggerPatterns" language="rust" filename="src/triggers.rs" />
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<h4 class="font-semibold mb-2 text-primary-400">Audit Trail</h4>
<p class="text-muted text-sm">Tracks all changes with who, what, when, and before/after values</p>
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<h4 class="font-semibold mb-2 text-primary-400">Soft Delete</h4>
<p class="text-muted text-sm">Converts DELETE to UPDATE, preserving data with a deleted_at timestamp</p>
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<h4 class="font-semibold mb-2 text-primary-400">Updated At</h4>
<p class="text-muted text-sm">Automatically updates a timestamp column on any modification</p>
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<h4 class="font-semibold mb-2 text-primary-400">Validation</h4>
<p class="text-muted text-sm">Enforce business rules with custom check constraints</p>
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<h2 class="text-2xl font-semibold mb-4">MongoDB Change Streams</h2>
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Change streams provide real-time notifications of data changes in MongoDB.
They're the MongoDB equivalent of triggers.
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<app-code-block [code]="mongoChangeStream" language="rust" filename="src/main.rs" />
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<strong>Note:</strong> Change streams require a MongoDB replica set. Save resume tokens
to recover from disconnections without missing events.
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<h2 class="text-2xl font-semibold mb-4">MySQL Event Scheduler</h2>
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Schedule recurring or one-time tasks with MySQL's EVENT system.
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<app-code-block [code]="eventScheduler" language="rust" filename="migrations/events.rs" />
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<strong>Important:</strong> Ensure the event scheduler is enabled:
<code class="px-1 bg-surface-elevated rounded">SET GLOBAL event_scheduler = ON;</code>
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<h2 class="text-2xl font-semibold mb-4">MSSQL SQL Server Agent</h2>
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Define SQL Server Agent jobs for scheduled tasks with multiple steps.
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<app-code-block [code]="sqlAgentJob" language="rust" filename="migrations/jobs.rs" />
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<h2 class="text-2xl font-semibold mb-4">MongoDB Atlas Triggers</h2>
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Cloud-based triggers that run Atlas Functions in response to database changes.
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<app-code-block [code]="atlasTrigger" language="rust" filename="migrations/atlas.rs" />
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<h2 class="text-2xl font-semibold mb-4">Trigger Migrations</h2>
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Version control your triggers alongside your schema.
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<app-code-block [code]="triggerMigration" language="rust" filename="migrations/triggers.rs" />
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<h2 class="text-2xl font-semibold mb-4">Best Practices</h2>
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<h4 class="font-semibold mb-2 text-success-400">Keep Triggers Fast</h4>
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Triggers run synchronously within the transaction. Long-running operations should
be handled asynchronously via queues or change streams.
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<h4 class="font-semibold mb-2 text-success-400">Avoid Cascading Triggers</h4>
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Be careful with triggers that modify tables with their own triggers.
This can create hard-to-debug infinite loops.
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<h4 class="font-semibold mb-2 text-warning-400">Test Trigger Behavior</h4>
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Triggers can have subtle interactions with transactions and constraints.
Always test with realistic data volumes.
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<h4 class="font-semibold mb-2 text-info-400">Document Side Effects</h4>
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Triggers introduce "invisible" behavior. Document all triggers clearly so
developers know what happens automatically.
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