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buildEdgeGroupExpression.php

Functions

buildEdgeGroupExpression() : string: Compiles the grouping dimension of a **relation**: the value a document is grouped by when that value lives on the document at the other end of an edge.

buildEdgeGroupExpression()

Compiles the grouping dimension of a **relation**: the value a document is grouped by when that value lives on the document at the other end of an edge.


    
                    buildEdgeGroupExpression(string $key, array<string|int, mixed> $definition, array<string|int, mixed>|string $path[, string $startVertex = AQL::DOC ][, ContainerInterface|null $container = null ]) : string

The expression is a sub-query written inline in the COLLECT, and it has to be, because a grouped query never projects. The LET a projected relation emits — the one a relational sort names — is produced by returnFields(), which a grouped query does not call: doc is consumed by the COLLECT, so there is nothing to project and no variable to reach for. The dimension therefore carries its own traversal:

COLLECT author = FIRST( FOR author_v IN OUTBOUND doc articles_authors RETURN author_v.name )
AGGREGATE total = SUM( doc.amount )

FIRST() is what makes the dimension a scalar, and it is why only a singular relation may be grouped on. The two alternatives were measured, and neither is acceptable:

keeping the sub-query as an array groups by the combination — three buckets (["Alice"], ["Alice","Zoe"], ["Zoe"]) for two authors;
unwinding the relation with a FOR before the COLLECT duplicates the document once per related vertex, which inflates every other aggregate of the same COLLECT: over three documents worth 10, 20 and 30, a SUM answers 70 where the truth is 60, because the two-author document is counted twice.

The declaration is read through the same shared doors as the list — the depth range, the row scope (AQL::WHERE / AQL::PRUNE) and the traversal options — so a grouped dimension describes exactly the relation the list projects. Read differently, it would put a label next to rows that contradict it.

Parameters

$key : string: The dimension key; names the traversal variable (<key>_v).
$definition : array<string|int, mixed>: The edge definition (AQL::MODEL, AQL::DIRECTION, …).
$path : array<string|int, mixed>|string: The field of the related document carrying the value.
$startVertex : string = AQL::DOC: The document the traversal departs from.
$container : ContainerInterface|null = null: Resolves an AQL::MODEL given by container id.

Return values

string —

The FIRST( FOR … RETURN … ) expression.

buildEdgeGroupExpression.php

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buildEdgeGroupExpression()

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