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Examples of eval function use [message #1760243]

Tue, 25 April 2017 07:22

Ilya Ermolin

Messages: 1
Registered: April 2017

Junior Member

Hi!

A want to deeply anderstand OQL in MAT for use and get some trouble to make some computations in MAT itself.

So I want to anderstand what I can do with eval function - for completness of functions. Any Info will be great!

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Re: Examples of eval function use [message #1764689 is a reply to message #1760243]

Thu, 01 June 2017 12:02

Andrew Johnson

Messages: 205
Registered: July 2009

Senior Member

I put it in as I was trying some complex operations and the grammar wouldn't let me do some things.
E.g.
SELECT t FROM OBJECTS (SELECT s, s.count FROM java.lang.StringBuilder s ) t
gives the error:
Query:
SELECT t FROM OBJECTS (SELECT s, s.count FROM java.lang.StringBuilder s ) t

Problem reported:
Sub-Select must return an object list: SELECT s, s.count FROM java.lang.StringBuilder s

whereas
SELECT t FROM OBJECTS ( eval((SELECT s, s.count FROM java.lang.StringBuilder s )) ) t
did work, though the result:
t
-------------------------------------------------------------------
org.eclipse.mat.parser.internal.oql.OQLQueryImpl$ResultSet@b4096667
-------------------------------------------------------------------
wasn't particular useful.

Sometimes adding extra parentheses also worked:
SELECT t FROM OBJECTS ((SELECT s, s.count FROM java.lang.StringBuilder s )) t
but the extra ones got stripped out when the OQL was executed, so redoing the query failed.

I still haven't found a useful case since I relaxed the grammar to allow a SimpleExpression instead of a PathExpression or EnvVarPathExpression for a SelectItem and a ConditionalOrExpression for a FROM OBJECTS.

Perhaps a SELECT FROM OBJECTS of a subselect returning SelectItems should iterate over that (accessing each SelectItem as an array or map??), but I would like to see a use case.

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