Understanding "no viable alternative ..." errors

Discussion:

Pritam

2010-01-13 17:09:07 UTC

While executing the following rule,

rule "home dummy"
when
pointId: Point(page == "home", region ="center-content")
content: Content(id=="adslot")
properties["type"]=="ad" from content
then
filter.put(content.id, true);
end

I get the following error:
[ERR 101] Line 16:46 no viable alternative at input 'EQUALS' in rule "home
dummy" in pattern PointId[18,16]: [ERR 102] Line 18:16 mismatched input
'"type"' expecting ']' in rule "home dummy" in pattern properties

The documentation explains that this is the most common error but I still
struggle to understand the correct grammar for writing rules. Can anyone
point me to a good resource (I even read the book "drools 5) for writing the
following rule in a drl format?

" If a Point has a page, "home" and region, "center-content" and the Content
id is "adslot" with a property, type as "ad" then filter the Content (using
a global map and passing a boolean flag)

Thanks

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Esteban Aliverti

2010-01-13 17:13:54 UTC

Permalink

Did you miss an = sign in region??

rule "home dummy"
when
pointId: Point(page == "home", region =*=*"center-content")
content: Content(id=="adslot")
properties["type"]=="ad" from content
then
filter.put(content.id, true);
end

Best,

Post by Pritam
While executing the following rule,
rule "home dummy"
when
pointId: Point(page == "home", region ="center-content")
content: Content(id=="adslot")
properties["type"]=="ad" from content
then
filter.put(content.id, true);
end
[ERR 101] Line 16:46 no viable alternative at input 'EQUALS' in rule "home
dummy" in pattern PointId[18,16]: [ERR 102] Line 18:16 mismatched input
'"type"' expecting ']' in rule "home dummy" in pattern properties
The documentation explains that this is the most common error but I still
struggle to understand the correct grammar for writing rules. Can anyone
point me to a good resource (I even read the book "drools 5) for writing the
following rule in a drl format?
" If a Point has a page, "home" and region, "center-content" and the Content
id is "adslot" with a property, type as "ad" then filter the Content (using
a global map and passing a boolean flag)
Thanks
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Esteban Aliverti

David Sinclair

2010-01-13 17:15:01 UTC

Permalink

You are missing another = sign for your region check, i.e. pointId:
Point(page == "home", region == "center-content")

Also, is there a join between the Point and the Content? Otherwise you'll
have the cartesian product of points and content

Edson Tirelli

2010-01-13 17:15:48 UTC

Permalink

The error simply means that your syntax is incorrect and the parser
could not understand the character at line 16, character 46. In this case,
you are using "=" instead of the correct "==":

pointId: Point(page == "home", region == "center-content")

Also, remember that constraints can only exist inside a pattern, so your
"properties" constraint must go inside the proper pattern that I guess is
"Content"

content: Content(id=="adslot", properties["type"]=="ad" )

[]s
Edson

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JBoss Drools Core Development
JBoss by Red Hat @ www.jboss.com

Pritam

2010-01-13 17:27:15 UTC

Permalink

Ah, that was an oversight. After fixing that, I now get ...

mismatched input '"type"' expecting ']' in rule "filter content if
advertisement" in pattern properties

Is something wrong with this mvel syntax?
properties["type"]=="ad" from content

Post by Pritam
While executing the following rule,
dialect "mvel"
import xxx.*
import java.util.*
global HashMap filter
rule "filter content if advertisement"
when
point: Point(page == "home", region ="center-content")
content: Content(id=="adslot")
properties["type"]=="ad" from content
then
filter.put(content.id, true);
end
[ERR 101] Line 16:46 no viable alternative at input 'EQUALS' in rule
"filter content if advertisement" in pattern Point[18,16]: [ERR 102] Line
18:16 mismatched input '"type"' expecting ']' in rule "filter content if
advertisement" in pattern properties
The documentation explains that this is the most common error but I still
struggle to understand the correct grammar for writing rules. Can anyone
point me to a good resource (I even read the book "Drools 5" by Packt) for
writing the following rule in a drl format?
" If a Point has a page, "home" and region, "center-content" and the
Content id is "adslot" with a property, type as "ad" then filter the
Content (using a global map and passing a boolean flag)
Thanks

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Andreas Volz

2010-01-14 12:00:05 UTC

Permalink

Just have a look at Edson's answer to your first mail:

"Also, remember that constraints can only exist inside a pattern, so your
"properties" constraint must go inside the proper pattern that I guess is
"Content"

content: Content(id=="adslot", properties["type"]=="ad" )"

Cheers,
Andreas

Post by Pritam
Ah, that was an oversight. After fixing that, I now get ...
mismatched input '"type"' expecting ']' in rule "filter content if
advertisement" in pattern properties
Is something wrong with this mvel syntax?
properties["type"]=="ad" from content

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Sent from the Drools - User mailing list archive at Nabble.com.

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