Re: [rules-users] Maps in Drools
Edson Tirelli schrieb:
Andre,
The misunderstanding here is that the LHS, except for code blocks
like "eval", "return value expressions" and "accumulate code
blocks",
are all "Drools Language". When you use the "dialect" attribute in a
rule or package you are telling the compiler what dialect (MVEL or Java)
you will use inside these code blocks mentioned previously + the
language for the RHS.
Good that you clear that up, thanks.
In other words:
Map( this["type"] == "Point", $x : this["x"], size == 5 )
I thought this is only possible when one declares the dialect MVEL.
Now I understand that what you just wrote also results in a valid rule,
even when MVEL is not set.
In your code above you:
1. check if this.get("type").equals("Point")
2. you set $x to the value of this.get("x")
3. check if this.size == 5
where I interpret 3. as calling the size() method of java.util.Map.
Was that right so far?
Everything you see in the previous expression is "Drools
language",
does not matter if you set the dialect to java or mvel in the rule. It
happens that Drools uses the same map syntax as MVEL (and a lot of other
scripting languages). Also, we know, that drools implementation will
resolve the first 2 above expressions in MVEL behind the scenes, and the
3rd will be resolved nativelly, but that is not something users should
have to worry about, since they are writing it in "Drools Language".
Yes, I understand.
Only with the middle part I still have some problems.
As you used it, $x : this["x"] it works for me.
A minor issue I have with this, but we can ignore that for now, is, that
this will be interpreted.
The real problem for me is: it only works when between the brackets
there is a literal string.
I however can't do that, because my lib should support the general case,
where between the brackets there could be any type of object (which I
would pass in via a global var).
If they write an eval, THEN they need to differentiate between
MVEL
and Java according to the chosen dialect.
rule xyz
dialect "mvel"
when
eval( ...here you write MVEL code... )
then
// here you write MVEL code
end
rule xyz2
dialect "java"
when
eval( ...here you write JAVA code... )
then
// here you write JAVA code
end
Very good, thanks again for clearing this up.
André
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