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https://issues.apache.org/jira/browse/JENA-2020?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17255239#comment-17255239
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Andy Seaborne commented on JENA-2020:
-------------------------------------
Look at the current code for inspiration: {{OpFilter}} for example or another
{{Op1}}.
{{input}} is passed from outside e.g. {{OpSequence}}. If the query is purely
bottom-up at this point, it will be the root which is one row, no bindings.
Calls {{QueryIterator qIter = exec(base, input) ;}} to execute the sub-op,
using the external;y passed in {{QueryIterator}} (which may be the root - i.e.
nothing). It now has the QueryIterator for the BGP and it filters that with
{{QueryIterFilterExpr}}.
Looks like you want to do the same. Execute the sub-op. Try a few cases and
stop in the debugger.
{noformat}
protected QueryIterator execute(OpFilter opFilter, QueryIterator input) {
ExprList exprs = opFilter.getExprs() ;
Op base = opFilter.getSubOp() ;
QueryIterator qIter = exec(base, input) ;
for (Expr expr : exprs)
qIter = new QueryIterFilterExpr(qIter, expr, execCxt) ;
return qIter ;
}
{noformat}
> Purpose of EvaluatorSimple and OpExecutor
> -----------------------------------------
>
> Key: JENA-2020
> URL: https://issues.apache.org/jira/browse/JENA-2020
> Project: Apache Jena
> Issue Type: Question
> Components: ARQ
> Reporter: Martin Pekár
> Priority: Major
> Original Estimate: 1h
> Remaining Estimate: 1h
>
> I am in the midst of adding a new operator in the transformation of OpBGP. I
> am now trying to implement the execution of the operator in the query plan,
> but I am now slightly confused about the purpose of EvaluatorSimple used in
> EvaluatorDispatch and OpExecutor. At the moment, it seems like they are doing
> the same thing. The difference seems to be that OpExecutor stores the result
> of applying the operator in a QueryIterator, whereas EvaluatorSimple stores
> its result in a Table of bindings.
> Can someone give me an explanation of purposes of these two classes and how
> they should be used?
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