Drools compare if one list contains element from another list - drools

Question

I have got below structure in Java:
public class Request {
List<Product> product;
List<Account> accounts;
}
public class Product {
String productIdOne;
String productIdTwo;
String productTax;
}
public class Account {
List<ProductRelationship> productsRelationship;
}
public class ProductRelationship {
String productIdOne;
String productIdTwo;
}
And the request is the fact object send to drools. I am wondering how I can check if there is at least one product that productTax is set to 'true' and there is a relationship between one account and one product. In other words, if there is a product with tax set to true and at least one account contains a relationship with this product (by productIdOne and productIdTwo) then the rule result should pass;
The main issue is that the list of the product relationship is inside the account list.
Thanks for any advice

Answer 1

You have a rather straight-forward set of conditions, so it is possible to write a relatively simple rule to check them. I will consider each condition separately and then combine them into a final rule.
As you wrote:
there is at least one product that productTax is set to 'true'
Now, as you mentioned, your rule inputs are the Request instance which contains two lists (products, accounts.) We'll start by declaring that:
rule "Account exists with taxed product"
when
Request( $products: product != null,
$accounts: accounts != null )
Next, we want to find the taxed product. If we only wanted to prove the existence of the product, we could use an exists( ... ) condition, which is extremely fast. However since we want to do further comparisons, we'll want to actuall find the product with this condition and save a reference to it.
$taxedProduct: Product( productTax == "true" ) from $products
I've assumed here that any value other than exactly "true" is indicative of an untaxed product. You should adjust as needed (and possibly consider changing this type to a boolean.)
The next condition is to find the account:
there is a relationship between one account and [the taxed] product
First, we'll need to update our $taxedProduct declaration and get references to its ids:
$taxedProduct: Product( productTax == "true",
$id1: productIdOne,
$id2: productIdTwo ) from $products
Now we need to find an account with a matching relationship.
$account: Account( $relationships: productsRelationship != null ) from $accounts
exists( ProductRelationship( productIdOne == $id1,
productIdTwo == $id2 ) from $relationships )
Here, I used an exists condition for the relationship because we don't need to refer to the relationship itself ever again, just verify that the relationship exists. I did declare a variable $account to point to the account that has the product relationship.
Putting it all together, we have:
rule "Account exists with taxed product"
when
Request( $products: product != null,
$accounts: accounts != null )
$taxedProduct: Product( productTax == "true",
$id1: productIdOne,
$id2: productIdTwo ) from $products
$account: Account( $relationships: productsRelationship != null ) from $accounts
exists( ProductRelationship( productIdOne == $id1,
productIdTwo == $id2 ) from $relationships )
then
// We have a taxed product $taxedProduct
// and an associated account $account
end
When I first started with Drools I found it difficult to wrap my head around the way it treated objects in lists, which is why the ProductRelationship sub-list seems like a tricky issue on its face. What Drools is going to do is iterate through the $products list and find those Product instances that meet our criteria (namely, have productTax == "true".) Once it has found these taxed products, it then similarly goes through the $accounts list and finds all Accounts that meet the criteria (which have a productsRelationship list.) Then for each of those accounts, it is going to test that there exists a relationship as we've defined.
This is a simplified explanation, of course, but it helps to form a mental model of roughly what Drools is doing here. In reality Drools is much more efficient than then roughly O(n^3) workflow I've just described.
An interesting thing you should keep in mind is that this rule is not going to "stop" as soon as it finds a match. If you have two taxed products that have a relationship to a single account, this rule will fire twice -- once for each taxed product. Or, alternatively, if you have one taxed product and two accounts that have a relationship to it, the rule will fire twice (once for each account.) Basically, the rule will fire once for each "match" it finds in the given request.

Answer 2

can you try this following
rule "sample"
no-loop
when
request:Request(accountList: accounts)
request1:Request(productList: product)
Account(productsRelationshipList:ProductRelationship) from accountList
Product(productId contains productsRelationshipList, productTax = true ) from productList
then
System.out.println("Rule fired satisfied");
end