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Drools: difference between contains and memberof

I'm reading Drools 6.4.0 documentation. I'm not sure to have understood the difference between contains and memberof operators: both work with collections and it seems that the only difference is that contains expect the contained object on the right side while memberof expect it on the left side, so they would be equivalent but I'm afraid I'm missing something.

Solution

  • This exemple is taken from Laune's answer to : Drools: Match local string from array in LHS of rule

    rule "ruleY"
when
    Data( $los: listOfStrings )
    MyObject( string memberOf $los ) 
then
    //do stuff
end
rule "ruleY"
when
    MyObject( $s: string ) 
    Data( listOfStrings contains $s )
then
    //do stuff
end

    They are complementary. Use the one or the other depending of the data you are having and the most logical way to express things.