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https://issues.apache.org/jira/browse/SOLR-8458?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15072395#comment-15072395
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Dennis Gove commented on SOLR-8458:
-----------------------------------
What if we were to make substitution parameters first class citizens similar to
named parameters? During the parsing in ExpressionParser we could create
instances of StreamExpressionSubstitutionParameters which exist as first class
citizens of an StreamExpression object. This would allow us to send (in the
example in the description) "expr", "left", and "right" through the
ExpressionParser. Then, a simple method can be added to the StreamFactory which
accepts a main expression and a map of names => expressions. It could then
iterate over parameters of the main expression doing replacements until there
are no more instances of StreamExpressionSubstitutionParameter in the main
expression. Some checks for infinite loops would have to be added but those are
relatively simple.
This approach would allow the logic to exist outside of the StreamHandler which
I think would be beneficial for the SQL Handler.
It might also allow for some type of prepared statements with "pre-compiled"
pieces (similar to what one might see in a DBMS). For example, this might be
beneficial in a situation where some very expensive part of the expression is
static which you want to perform different rollups or joins or whatever with.
An optimizer could hang onto the static results in a RepeatableStream (doesn't
exist yet) and substitute that into some other expression.
> Parameter substitution for Streaming Expressions
> ------------------------------------------------
>
> Key: SOLR-8458
> URL: https://issues.apache.org/jira/browse/SOLR-8458
> Project: Solr
> Issue Type: Improvement
> Reporter: Joel Bernstein
> Priority: Minor
> Attachments: SOLR-8458.patch
>
>
> As Streaming Expressions become more complicated it would be nice to support
> parameter substitution. For example:
> {code}
> http://localhost:8983/col/stream?expr=merge($left, $right,
> ...)&left=search(...)&right=search(...)
> {code}
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