SyteLine Event Handler Development Complete Guide
Event handlers are the primary mechanism for injecting custom business logic into SyteLine's transaction pipeline without modifying base code. They fire at precise points during IDO operations and form interactions, allowing you to validate data, enforce business rules, trigger integrations, and audit changes. This guide covers the complete event handler development lifecycle with patterns for production-grade implementations.
Event Types, Timing, and Registration
SyteLine supports four event categories: IDO pre-events fire before a database operation commits (InsertPre, UpdatePre, DeletePre), IDO post-events fire after successful commit (InsertPost, UpdatePost, DeletePost), form load events fire when data is loaded into a form, and custom events that you define and raise programmatically. Register event handlers through the Event Handler Configuration form (Menu Path: Application > Event Handlers). Each registration specifies the target IDO, the event type, the handler assembly and class name, and the execution priority (lower numbers execute first). Pre-events can cancel the operation by setting e.Cancel = true on the event args, while post-events cannot roll back the already-committed transaction. The critical architectural decision is choosing between pre-events for validation and data enrichment versus post-events for notifications and downstream triggers.
- IDO pre-events (InsertPre, UpdatePre, DeletePre) fire before commit and can cancel via e.Cancel = true
- IDO post-events (InsertPost, UpdatePost, DeletePost) fire after commit and cannot roll back
- Register handlers in Application > Event Handlers with target IDO, event type, and priority order
- Execution priority is numeric—lower values execute first when multiple handlers target the same event
Handler Implementation Patterns
Event handler classes must inherit from Mongoose.IDO.IDOEventHandlerBase and implement the specific event method (e.g., OnInsertPre, OnUpdatePost). Within the handler, access the affected record's property values through the EventArgs.Current property collection. For pre-events, modify property values by setting them on EventArgs.Current before returning—Mongoose will include your changes in the pending transaction. For cross-entity validation (e.g., checking inventory availability when a sales order line is inserted), use the IDO runtime from the handler's context to query other IDOs: this.Context.Commands.LoadCollection("SL.SLItems", ...). Always wrap handler logic in try-catch blocks because unhandled exceptions in event handlers will abort the entire transaction and present users with a generic error. Set a meaningful error message on EventArgs.ErrorMessage to provide actionable feedback.
- Inherit from Mongoose.IDO.IDOEventHandlerBase and override the specific event method
- Access record data through EventArgs.Current property collection for reading and writing values
- Use this.Context.Commands.LoadCollection() for cross-entity validation within event handlers
- Always set EventArgs.ErrorMessage with actionable text when canceling operations via e.Cancel
Performance Optimization and Testing
Event handlers execute synchronously within the transaction pipeline, so performance directly impacts user experience. A handler that takes 3 seconds on a sales order line insert means every line entry takes 3 extra seconds. Profile handler execution time using Stopwatch logging and set a hard budget of 500ms per handler. For handlers that need to perform slow operations (external API calls, complex queries), implement an async dispatch pattern: write a record to a custom queue table in the pre/post event, then process the queue asynchronously via a background task. Test handlers by creating unit tests that mock the IDO event context using the Mongoose.IDO.Testing namespace, and integration tests that exercise the full event chain through IDO web service calls. Test edge cases including concurrent updates, null property values, and high-volume bulk operations where hundreds of events fire in rapid succession.
- Set a 500ms execution budget per handler—anything slower should use async queue dispatch
- Implement async patterns by writing to a queue table and processing via background tasks
- Write unit tests using mocked IDO event context from Mongoose.IDO.Testing namespace
- Test under load: bulk operations firing hundreds of events expose race conditions and timeouts
Building event handlers for SyteLine? Our team has delivered 500+ production event handlers for enterprise manufacturers—let us help.
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