地图迭代Drools Drl列表

Question

I am trying to iterate a list of map as below:

[
  {
    "endOffset": 2913,
    "coreference": "Tehran",
    "entity": "a country",
    "beginOffset": 2904
  },
  {
    "endOffset": 3055,
    "coreference": "Bashar al-Assad",
    "beginOffset": 3052
  },
  {
    "endOffset": 3130,
    "coreference": "Bashar",
    "beginOffset": 3128
  }
]

The code block, I am executing is as below:

PojoCorefList pojoCorefList=new PojoCorefList();
List<Map<String,String>> corefList=new ArrayList<Map<String,String>>();
Map<String,String> testMap=new LinkedHashMap<>();
testMap.put("beginOffset", "3052");
testMap.put("coreference", "Bashar al-Assad");
testMap.put("endOffset", "3055");
corefList.add(testMap);
Map<String,String> testMap2=new LinkedHashMap<>();
testMap2.put("beginOffset", "3130");
testMap2.put("coreference", "Bashar");
testMap2.put("endOffset", "3128");
corefList.add(testMap2);
Map<String,String> testMap3=new LinkedHashMap<>();
testMap3.put("beginOffset", "2913");
testMap3.put("coreference", "Tehran");
testMap3.put("endOffset", "2904");

corefList.add(testMap3);

pojoCorefList.setCityPlaces(corefList);
ksession.insert(pojoCorefList);

Here is the PojoCorefList class as below:

public static class PojoCorefList {
    private List<Map<String,String>> cityPlaces;
    public List<Map<String,String>> getCityPlaces() {
         return cityPlaces;
    }

    public void setCityPlaces(List<Map<String,String>> cityPlaces) {
         this.cityPlaces = cityPlaces;
    }
}

The drl syntax, I have tried is as below :

rule "List of Maps Testing"
    salience 1

    when
        $c : PojoCorefList($coref : cityPlaces)
    $item : List() from $coref
    entry : Entry() from $item.entrySet()
    //value: String() from entry.getValue()
    //Boolean(booleanValue :true) from value=="Tehran"

    then
      System.out.println("List Maps Testing: list is - "+$item);
end 

I believe, I am iterating $coref list and now I should be having a map but if I try to get entrySet() from $item, I am getting exception as below:

Unable to Analyse Expression $item.entrySet():
[Error: unable to resolve method using strict-mode: java.util.List.entrySet()]
[Near : {... $item.entrySet() ....}]
                   ^ : [Rule name='List of Maps Testing']

Answer 1

Drools doesn't understand generics. But if you supply the correct classes, it should work. Note that from collection iterates the collection.

  $c : PojoCorefList($coref : cityPlaces)
  $m : HashMap() from $coref  // cityPlaces are lists of Maps
  entry : Entry() from $m.entrySet()

or use

  value : String() from $m.values()

(This may depend on the Drools version.)

Answer 2

You can also use OOPath syntax, if you are on Drools 6.4 and higher. It much improves the LHS compactness.

Your case can look like just this one constraint:

$c : PojoCorefList($entry : /cityPlaces/entrySet)

where $entry is of type Entry(). You can read more about OOPath here: https://docs.jboss.org/drools/release/6.5.0.Final/drools-docs/html/ch10.html#d0e13581