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https://issues.apache.org/jira/browse/SOLR-11600?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16260797#comment-16260797
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Amrit Sarkar commented on SOLR-11600:
-------------------------------------
Thank you [~joel.bernstein] for the explanation;
> Each expression has it's own set of rules for the parameters that it accepts
> so we can get very specific with how type safety is handled
I completely understand this by the following example
{code}
replace( fieldA, add( fieldB, if( eq(fieldC,0), 0, 1)))
{code}
This nested evaluation and operation is not possible to create with current
Java constructors available, as the constructors of evaluators and operations
have most just one type of constructor with {{StreamExpression}}
(StreamExpressionParameter interface) parameter which the evaluators or
operators doesn't implement (they implement Expressible interface).
{code}
public AddEvaluator(StreamExpression expression, StreamFactory factory)
throws IOException{
super(expression, factory);
if(containedEvaluators.size() < 1){
throw new IOException(String.format(Locale.ROOT,"Invalid expression %s -
expecting at least one value but found
%d",expression,containedEvaluators.size()));
}
}
{code}
To accomodate the above request, strongly types java objects for all, we need
to create rule-based constructors for all the evaluators and operators, so that
those can be used in {{SelectStream}}.
> Add Constructor to SelectStream which takes StreamEvaluators as argument.
> Current schema forces one to enter a stream expression string only
> ---------------------------------------------------------------------------------------------------------------------------------------------
>
> Key: SOLR-11600
> URL: https://issues.apache.org/jira/browse/SOLR-11600
> Project: Solr
> Issue Type: Improvement
> Security Level: Public(Default Security Level. Issues are Public)
> Components: SolrJ, streaming expressions
> Affects Versions: 6.6.1, 7.1
> Reporter: Aroop
> Priority: Trivial
> Labels: easyfix
> Attachments: SOLR-11600.patch
>
>
> The use case is to be able able to supply stream evaluators over a rollup
> stream in the following manner, but with instead with Strongly typed objects
> and not steaming-expression strings.
> {code:bash}
> curl --data-urlencode 'expr=select(
> id,
> div(sum(cat1_i),sum(cat2_i)) as metric1,
> coalesce(div(sum(cat1_i),if(eq(sum(cat2_i),0),null,sum(cat2_i))),0) as
> metric2,
> rollup(
> search(col1, q=*:*, fl="id,cat1_i,cat2_i,cat_s", qt="/export", sort="cat_s
> asc"),
> over="cat_s",sum(cat1_i),sum(cat2_i)
> ))' http://localhost:8983/solr/col1/stream
> {code}
> the current code base does not allow one to provide selectedEvaluators in a
> constructor, so one cannot prepare their select stream via java code:
> {code:java}
> public class SelectStream extends TupleStream implements Expressible {
> private static final long serialVersionUID = 1L;
> private TupleStream stream;
> private StreamContext streamContext;
> private Map<String, String> selectedFields;
> private Map<StreamEvaluator, String> selectedEvaluators;
> private List<StreamOperation> operations;
> public SelectStream(TupleStream stream, List<String> selectedFields)
> throws IOException {
> this.stream = stream;
> this.selectedFields = new HashMap();
> Iterator var3 = selectedFields.iterator();
> while(var3.hasNext()) {
> String selectedField = (String)var3.next();
> this.selectedFields.put(selectedField, selectedField);
> }
> this.operations = new ArrayList();
> this.selectedEvaluators = new HashMap();
> }
> public SelectStream(TupleStream stream, Map<String, String>
> selectedFields) throws IOException {
> this.stream = stream;
> this.selectedFields = selectedFields;
> this.operations = new ArrayList();
> this.selectedEvaluators = new HashMap();
> }
> {code}
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