query 作用和語(yǔ)法

Drools 因其他靈活的 LHS 語(yǔ)法, 能實(shí)現(xiàn)非常強(qiáng)大的模式匹配功能, 這是 drools 規(guī)則的核心. Drools 通過(guò)提供 query 這種方式, 使得我們的java程序也可直接利用其強(qiáng)大的模式匹配功能.

query 定義很簡(jiǎn)單, 只要寫(xiě) LHS 部分即可, 語(yǔ)法為:

query "queryName"
   LHS
end

示例

drools 文件, 定義了一個(gè)無(wú)參query和一個(gè)帶參query:

package com.sample.rules
 
import com.sample.Order;

query "amount > 10"
    $order:Order(amount>10)
end 


query "any amount"(int $amount)
    $order:Order(amount>$amount)
end 

java 端, 調(diào)用query的示例

package com.sample;

import org.kie.api.KieServices;
import org.kie.api.runtime.KieContainer;
import org.kie.api.runtime.KieSession;
import org.kie.api.runtime.rule.QueryResults;
import org.kie.api.runtime.rule.QueryResultsRow;

/**
 * This is a sample class to launch a rule.
 */
public class DroolsTest {

	public static final void main(String[] args) {
		try {
			// load up the knowledge base
			KieServices ks = KieServices.Factory.get();
			KieContainer kContainer = ks.getKieClasspathContainer();
			KieSession kSession = kContainer.newKieSession("ksession-rules");

			Order order = null;
			order = new Order();
			order.setAmount(2);
			kSession.insert(order);

			order = new Order();
			order.setAmount(20);
			kSession.insert(order);

			order = new Order();
			order.setAmount(3);
			kSession.insert(order);

			// kSession.fireAllRules(); //call query 不需要fire rule

			// 查詢無(wú)參query			
			QueryResults queryResults1 = kSession.getQueryResults("amount > 10"); //第一個(gè)參數(shù)指定query名
			for (QueryResultsRow row : queryResults1) {
				Order order2 = (Order) row.get("$order");// get row item by bind variable
				System.out.println(order2);
			}

			System.out.println("===========");
			// 查詢帶參query
			QueryResults queryResults2 = kSession.getQueryResults("any amount", 10);  //第一個(gè)參數(shù)指定query名, 后面參數(shù)作為query的查詢參數(shù)
			for (QueryResultsRow row : queryResults2) {
				Order order2 = (Order) row.get("$order");// get row item by bind variable
				System.out.println(order2);
			}

			kSession.dispose();

			// System.out.println(order.getRealPrice());
		} catch (Throwable t) {
			t.printStackTrace();
		}
	}

}