I'm trying to write a rule to add an object to a collection if the collection already contained a certain object with a specific attribute. I developed a small example so maybe that will make more sense: Use Case: In a product shipping applicaiton, anytime a product with the name "cd1" is in the shipping order, a bonus product named "bonus_cd" needs to be added to the shipping order.  The bonus cd should not be added if it's already in the shipping order. Shipping Order: public class ShippingOrder {        private Set<Product> products;        public ShippingOrder() {}        public Set<Product> getProducts() {                return products;        }        public void setProducts(Set<Product> products) {                this.products = products;        } } Product: public class Product {        private String name;        public Product(){}        public String getName() {                return name;        }        public void setName(String name) {                this.name = name;        } } Rule: rule "AddBonusCd"        when                $so : ShippingOrder()                $productList : ArrayList(size == 1) from collect( Product(name matches "cd1|bonus_cd") from $so.products)        then                System.out.println("Adding Bonus Cd");                Set<Product> productSet = new HashSet<Product>($so.getProducts());                Product bonusCd = new Product();                bonusCd.setName("bonus_cd");                productSet.add(bonusCd);                modify($so) {                        setProducts(productSet);                } end The Shipping Order object is inserted as the fact. The rule is valid if only cd1 or cd_bonus is in the shipping order.  I only want the rule to run when cd1 is in the product set but cd_bonus is not. Makes sense? Thanks, J -- View this message in context: http://drools-java-rules-engine.46999.n3.nabble.com/collection-question-t... Sent from the Drools - User mailing list archive at Nabble.com. _______________________________________________ rules-users mailing list rules-users(a)lists.jboss.org https://lists.jboss.org/mailman/listinfo/rules-users

From: Wolfgang Laun <wolfgang.laun(a)gmail.com&gt; To: Rules Users List <rules-users(a)lists.jboss.org&gt; Date: 07/21/2010 02:02 AM Subject: Re: [rules-users] collection question Sent by: rules-users-bounces(a)lists.jboss.org Things would be smpler if you could avoid re-creating Product objects because adding an identical Object does not change the Set. (This could be implemented with the help of a global Map<String,Product>,) Second, overriding equals (and hashCode) in Product would also avoid adding an "evil twin" in your rule code - as it is! Even simpler is a solution where the relevant Product objects are inserted as facts, so that $cd1 : Product( name == "cd1" ) $bonus_cd : Product( name == "bonus_cd" ) $order : ShippingOrder( products contains $cd1, products not contains $bonus_cd ) is true (again, with equals and hashCode being overridden). Given your solution with collect, an additional eval testing for "bonus_cd" not being the name of the single Product in List $productList might be more efficient than iterating all products a second time. -W On 21 July 2010 00:41, javaj <jmilliro(a)ameritech.net&gt; wrote: > > I'm trying to write a rule to add an object to a collection if thecollection > already contained a certain object with a specific attribute. > > I developed a small example so maybe that will make more sense: > > Use Case: In a product shipping applicaiton, anytime a product with the name > "cd1" is in the shipping order, a bonus product named "bonus_cd" needs to be > added to the shipping order. The bonus cd should not be added if it's > already in the shipping order. > > Shipping Order: > > public class ShippingOrder { > > private Set<Product> products; > > public ShippingOrder() {} > > public Set<Product> getProducts() { > return products; > } > > public void setProducts(Set<Product> products) { > this.products = products; > } > > } > > Product: > > public class Product { > > private String name; > > public Product(){} > > public String getName() { > return name; > } > > public void setName(String name) { > this.name = name; > } > > } > > > Rule: > > rule "AddBonusCd" > > when > $so : ShippingOrder() > $productList : ArrayList(size == 1) from collect( Product(name matches > "cd1|bonus_cd") from $so.products) > then > System.out.println("Adding Bonus Cd"); > > Set<Product> productSet = new HashSet<Product> ($so.getProducts()); > > Product bonusCd = new Product(); > bonusCd.setName("bonus_cd"); > productSet.add(bonusCd); > > modify($so) { > setProducts(productSet); > } > end > > The Shipping Order object is inserted as the fact. > > The rule is valid if only cd1 or cd_bonus is in the shipping order. I only > want the rule to run when cd1 is in the product set but cd_bonus is not. > Makes sense? > > Thanks, > J > -- > View this message in context: http://drools-java-rules-engine. 46999.n3.nabble.com/collection-question-tp982769p982769.html > Sent from the Drools - User mailing list archive at Nabble.com. > _______________________________________________ > rules-users mailing list > rules-users(a)lists.jboss.org > https://lists.jboss.org/mailman/listinfo/rules-users > _______________________________________________ rules-users mailing list rules-users(a)lists.jboss.org https://lists.jboss.org/mailman/listinfo/rules-users