使用 Drools 规则进行实体验证

Question

Can i validate an object for primary key values using Drools rule? Suppose i have one Object called Person with two primary keys personId and PersonNumber and many other fields like age,occupation etc. I need to create a Drools rule for validate the object Person for primary key validation ( Primary key shouldn't be not null).

if it is possible i have one more doubt. Can i make the the Drools rule as generic rule for validating other objects also ( it should be dynamic since all fields will different with respect to other object).

If anyone have suggestion on this please make a comment here.

Happy Coding!!

Answer 1

You can do a null check of course. But if this is something being inserted into a database that should really be taken care of by database constraints.

Anyway, using your example with an object Person and two fields personId and PersonNumber (ignoring the other fields because they're not immediately relevant.) I will assume the class and its getters look like this:

class Person {
  private Integer personId, PersonNumber;
  public Integer getPersonId() {
    return personId;
  }
  public Integer getPersonNumber() {
    return PersonNumber;
  }
}

Then you can write a rule checking that there is a Person with either personId or PersonNumber null:

rule "Person with either personId or PersonNumber null"
when
  exists( Person( personId == null || personNumber == null ))
then
  System.out.println("Person has either null personId or PersonNumber");
end

Note that if you wanted to check that both personId and PersonNumber are null, the rule would be a little different; you'd not use the || operator, but instead use the comma and:

rule "Person with both personId and PersonNumber null"
when
  exists( Person( personId == null, personNumber == null ))
then
  System.out.println("Person has null personId and null PersonNumber");
end

Alternatively, if I misunderstood what you means by Primary key shouldn't be not null such that you want the fields to be null so they can be auto-set by the database, then you could just invert the null check to a not null check either by replacing exists with not :

not( Person( personId == null || personNumber == null ))
not( Person( personId == null, personNumber == null ))

... or by swapping the == to !== .

As to your question about making a generic rule, that's not possible with rules unless all of the objects you're validating share a base class or an interface, and the method to get the primary key(s) is part of the base class/interface. In theory you could use reflection and create a Drools function to map a set of requested fields to a null check, but this seems like an incredibly bad idea and extremely fragile.