You have stumbled upon another exge case in the wonderfuly confusing world
of how Solr's "Document" (and "Field") APIs have long standing behavior to
try and be helpful when you want to specity a "List<Thing>" as *A* single
field value -- something that was never intended to be supported, and many
places in solr assume you ment for *each* of those "Things" to be
individual field values (in a multi-valued field) ...
https://issues.apache.org/jira/browse/SOLR-17974
: Date: Fri, 6 Feb 2026 12:07:29 +0100
: From: Nicolò Rinaldi <[email protected]>
: Reply-To: [email protected]
: To: [email protected]
: Subject: Clarification on matrix flattening behavior in
: RemoveBlankFieldUpdateProcessorFactory
:
: Hi
:
: I’m here to ask for some clarification about a behaviour that I encountered
: while trying to index matrices with RemoveBlankFieldUpdateProcessorFactory in
: the update processor chain, expecting an error since this syntax isn't
: supported in Solr. Here's an example: if I try to index a multivalued field
: with values [["cat", "dog"], ["lemon", "orange"]], the field is modified to
: ["cat", "dog", "lemon", "orange"]—flattening the 2x2 "matrix" into a 4-item
: vector. This flattening seems to happen in the mutate function
:
<https://github.com/SeaseLtd/solr/blob/c99af207c761ec34812ef1cc3054eb2804b7448b/solr/core/src/java/org/apache/solr/update/processor/FieldValueMutatingUpdateProcessor.java#L60>
: of FieldValueMutatingUpdateProcessor.
:
: This allows the field to be populated even though the syntax is incorrect.
: Is there a reason for this behaviour?
:
: Thanks,
:
: Nicolò
:
-Hoss
http://www.lucidworks.com/
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