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复杂规则编写

Table of Contents

条件元素

元素 说明

and

LHS 有多个 Fact 且所有条件都满足，如果 LHS 只包含 and，则 and 可以省略.

rule "Using the and conditional"
    when
        Cheese(cheeseType : type) and
        Person(favoriteCheese == cheeseType)
    then

or

LHS 有多个 Fact，只需任意一个条件满足.

rule "Using the or conditional"
    when
        Person(favoriteCheese == "Swiss") or
        (Person(favoriteCheese == "Cheddar") and Mouse(favoriteCheese == "Swiss"))
    then

eval

语义元素，用来包装布尔型变量，例如 eval(true).

rule "Using the eval element"
    when
        ob1 : Observation()
        ob2 : Observation(this != ob1)
        eval(weightedAverage(ob1.getVal(),ob2.getVal(),ob1.getPer(),ob2.getPer()) < .1)
    then

exists

判断特定 Fact 是否存在.

rule "Using the exists conditional"
    when
        customer : Customer()
        order: Order(customerId == customer.customerId)
        exists OrderItem(orderId == order.orderId, itemStatus == "out_of_stock")
    then

not

特定 Fact 不存在存在

rule "Using the exists conditional"
    when
        customer : Customer()
        order: Order(customerId == customer.customerId)
        not OrderItem(orderId == order.orderId, itemStatus == "out_of_stock")
    then

from

用于 Fact 之间的关联。

rule "Using the from element for integration"
    when
        order : Order()
        item : OrderItem( value > 100 ) from order.items
    then
        item.setValue(item.getValue() * 0.8);
end

forall

是否所有 Fact 满足判断条件

rule "Using the forall element"
    when
    not (
        forall( emp : Employee() HealthCare( employee == emp ) DentalCare( employee == emp ) )
    )
    then

collect

处理集合，支持的集成类型包括: ArrayList, LinkedList, HashSet

rule "Using the collect conditional element"
when
    company : Company( name == 'Red Hat' )
    mothers : LinkedList()
               from collect( Person( gender == 'F', children > 0 )
                             from company.getPeople()
                           )
then

accumulate

对 collect 的加强，增加遍历，反转等功能

rule "Using the accumulate element"
when
    $order : Order()
    total : Number( doubleValue > 100 )
             from accumulate( OrderItem( order == $order,
                                         $value : value ),
                              sum( $value ) )
then

比较运算符

名称 说明

<, ⇐, >, >=, ==, =, !=

数学比较运算符

Person( age > 30 && < 40 )

matches

规则中引用正则表达式

Cheese( type matches "(Buffalo)?\\S*Mozarella" )

soundslike

类似于 ==

Cheese( name soundslike 'swish')

contains

集合或数组中是否存在某元素

CheeseCounter( cheeses contains "stilton" )
CheeseCounter( cheeses contains $var )

in

某元素是否在某元素集中

Person( $cheese : favoriteCheese )
Cheese( type in ( "stilton", "cheddar", $cheese ) )

memberOf

是否是集合或数组中的元素

CheeseCounter( cheese memberOf $matureCheeses )

两种 dialect 的比较

比较项 Java MVEL

Property access

 
user.getManager().getName()
 
user.manager.name

Collection and map access

 
user.get(5)
user.get("foobar")
 
user[5]
user["foobar"]/user.foobar

Property assignment

 
user.getManager().setName("name")
user.add("foo", "bar")
 
user.manager.name = "name"
user["foo"] = "bar"