Here are five things everyone should know about property expressions:

  • The runtime evaluates and applies property expressions only at certain times:
    • When loading
    • When saving
    • When the runtime calls validate on tasks
    • When the runtime calls execute on tasks
    • When a component calls AcquireConnection on connection managers
    • When a component calls GetEnumerator on foreach enumerators
  • They're available for almost all task, foreach enumerator, log provider, and connection manager writable properties.
  • They're available on a limited number of dataflow component properties.
  • They may not be used to modify variables.
  • They're automatically provided for all writable properties on custom components except for custom Data Flow task components.