The default value for this parameter to use if either there is no source field, or the value produced by the source is null. The default must be applied prior to scattering or evaluating valueFrom.
The unique identifier for this object.
A short, human-readable label of this object.
The method to use to merge multiple inbound links into a single array. If not specified, the default method is "merge_nested".
Only valid when type: File or is an array of items: File.
Only valid when type: Directory or is an array of items: Directory.
The method to use to choose non-null elements among multiple sources.
Specifies one or more workflow parameters that will provide input to the underlying step parameter.
To use valueFrom, StepInputExpressionRequirement must be specified in the workflow or workflow step requirements.
The input of a workflow step connects an upstream parameter (from the workflow inputs, or the outputs of other workflows steps) with the input parameters of the process specified by the run field. Only input parameters declared by the target process will be passed through at runtime to the process though additional parameters may be specified (for use within valueFrom expressions for instance) - unconnected or unused parameters do not represent an error condition.
Input object
A WorkflowStepInput object must contain an id field in the form #fieldname or #prefix/fieldname. When the id field contains a slash / the field name consists of the characters following the final slash (the prefix portion may contain one or more slashes to indicate scope). This defines a field of the workflow step input object with the value of the source parameter(s).
Merging multiple inbound data links
To merge multiple inbound data links, MultipleInputFeatureRequirement must be specified in the workflow or workflow step requirements.
If the sink parameter is an array, or named in a [workflow scatter](#WorkflowStep) operation, there may be multiple inbound data links listed in the source field. The values from the input links are merged depending on the method specified in the linkMerge field. If both linkMerge and pickValue are null or not specified, and there is more than one element in the source array, the default method is "merge_nested".
If both linkMerge and pickValue are null or not specified, and there is only a single element in the source, then the input parameter takes the scalar value from the single input link (it is *not* wrapped in a single-list).
* **merge_nested**
The input must be an array consisting of exactly one entry for each input link. If "merge_nested" is specified with a single link, the value from the link must be wrapped in a single-item list.
* **merge_flattened**
1. The source and sink parameters must be compatible types, or the source type must be compatible with single element from the "items" type of the destination array parameter. 2. Source parameters which are arrays are concatenated. Source parameters which are single element types are appended as single elements.
Picking non-null values among inbound data links
If present, pickValue specifies how to pick non-null values among inbound data links.
pickValue is evaluated 1. Once all source values from upstream step or parameters are available. 2. After linkMerge. 3. Before scatter or valueFrom.
This is specifically intended to be useful in combination with conditional execution, where several upstream steps may be connected to a single input (source is a list), and skipped steps produce null values.
Static type checkers should check for type consistency after inferring what the type will be after pickValue is applied, just as they do currently for linkMerge.
* **first_non_null**
For the first level of a list input, pick the first non-null element. The result is a scalar. It is an error if there is no non-null element. Examples: * [null, x, null, y] -> x * [null, [null], null, y] -> [null] * [null, null, null] -> Runtime Error
*Intended use case*: If-else pattern where the value comes either from a conditional step or from a default or fallback value. The conditional step(s) should be placed first in the list.
* **the_only_non_null**
For the first level of a list input, pick the single non-null element. The result is a scalar. It is an error if there is more than one non-null element. Examples:
* [null, x, null] -> x * [null, x, null, y] -> Runtime Error * [null, [null], null] -> [null] * [null, null, null] -> Runtime Error
*Intended use case*: Switch type patterns where developer considers more than one active code path as a workflow error (possibly indicating an error in writing when condition expressions).
* **all_non_null**
For the first level of a list input, pick all non-null values. The result is a list, which may be empty. Examples:
* [null, x, null] -> [x] * [x, null, y] -> [x, y] * [null, [x], [null]] -> [[x], [null]] * [null, null, null] -> []
*Intended use case*: It is valid to have more than one source, but sources are conditional, so null sources (from skipped steps) should be filtered out.