For Clause and Query

Since FQL 4.4 we split up the For-Select-Query syntax, to allow use for a For-Clause only.

For clause

The for-clause can be used as a top level filter clause, so that it can be used and combined with other filters, even followed by another for-clause.

Syntax

ForQuery: 'for' fhir-path-expression 

For-Select query

Functional

The for .. select .. statement:

• takes a set of nodes,
• productes a set of nodes by doing a filter and a projection from with the FHIRPath expression after the for,
• each of those nodes are then mapped using the field list after the select statement.
• groups each result set in a row node
• and produces a list of nodes of type row

Syntax:

ForQuery: 'for' fhir-path-expression 'select' (field-list|group)

A For Query can be used inside a field declaration or as part of a join.

...
   select,
      <field>, 
      <field>,
      for <fhir-path-expression> 'select' (field-list|group)
      

Purpose

The main purpose of a for-query is to allow to iterate directly over (multiple) sub nodes of a resource (type) instead of over the resources themselves. A typical use case could be to gather all invariants in different structure definitions in a package.

    from
       StructureDefinition
    for 
       differential.element
    select 
       id, 
       join constraint.expression
    order by id