Dafne: Documentation import

2026-08-06T13:36:50Z

Documentation import

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A [[Parameter]] is a user-defined value substituted into statements as <code>%u:name%</code>.

== Creating a parameter ==
# Open '''Author''' → '''Parameters'''.
# Click the create button above the list.
# Fill in the fields below and click '''Save'''.

== Fields ==
{| class="wikitable"
! Field !! Notes
|-
| '''ID''' || Assigned automatically; read-only.
|-
| '''Name''' || Mandatory and unique. Maximum 100 characters; letters, digits, space and <code>_</code>, <code>-</code>, <code>/</code>.
|-
| '''Description''' || Free text.
|-
| '''Connection''' || The connection used to evaluate the query. Leave as ''- None -'' for a parameter that only has a default value.
|-
| '''Default value''' || Maximum 2000 characters.
|-
| '''Query''' || An SQL statement returning the value. '''Only shown once a connection is selected.'''
|}

The '''Query''' field appearing only after a connection is chosen is the single thing most likely to cause confusion here. To create a query-based parameter, select the connection first.

== Static or query-based ==
* Leave '''Connection''' empty for a '''static''' parameter — it always resolves to its default value. Suitable for values that differ between environments but not between runs, such as a schema name or a file path.
* Set a connection and a query for a '''query-based''' parameter, whose value is obtained at planning time.

The '''Add variable''' button beside the query lists the placeholders available in it. These are the scenario-level placeholders, so a parameter can be derived from the state of previous processings. See [[Placeholders]].

== When the value is taken ==
Query-based parameters are evaluated '''once, when the processing is planned''' — not per task, and not again during the run. The value is therefore fixed for the whole processing, which keeps a long run internally consistent but means a parameter cannot carry information between tasks.

Only the parameters actually used by the tasks in the scenario are evaluated.

The values resolved for a given run are visible through '''Show processing details''' in the [[Monitor console]].

== Practical notes ==
* '''Keep a default value''' on query-based parameters where a sensible fallback exists. A parameter that resolves to nothing substitutes as empty rather than failing visibly.
* '''Names are global.''' Parameters are not scoped to a scenario, so a name like ''schema'' will not stay unambiguous. Use a qualified name.
* '''Quote in the statement, not the value.''' Substitution is textual and unquoted. Prefer passing parameters as procedure arguments over concatenating them into SQL — see [[Placeholders#Quoting]].
* Only the '''default value''' is available where a parameter is used in a scenario planning query, since the processing does not yet exist at that point.

== See also ==
* [[Parameter]]
* [[Placeholders]]
* [[Authoring items]]

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Dafne: Documentation import