MEL logical AND acting weird, order of operands matters?

Question

Can anyone explain why the following behavior occurs? Why does the order of the operands matter when using logical AND? Running on mule-ce 3.3.1.

The output is as follows:

true  
true  
false  
true


<?xml version="1.0" encoding="UTF-8"?>

<mule xmlns:http="http://www.mulesoft.org/schema/mule/http" xmlns="http://www.mulesoft.org/schema/mule/core" xmlns:doc="http://www.mulesoft.org/schema/mule/documentation" xmlns:spring="http://www.springframework.org/schema/beans" version="EE-3.4.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-current.xsd
http://www.mulesoft.org/schema/mule/core http://www.mulesoft.org/schema/mule/core/current/mule.xsd
http://www.mulesoft.org/schema/mule/http http://www.mulesoft.org/schema/mule/http/current/mule-http.xsd">

    <flow name="testFlow1" doc:name="testFlow1">
        <http:inbound-endpoint exchange-pattern="request-response" host="localhost" port="20005" path="test" doc:name="HTTP"/>

        <message-properties-transformer overwrite="true" scope="session" doc:name="Message Properties">
              <add-message-property key="productNumber" value="1" />
        </message-properties-transformer>

        <logger level="INFO" message="#[(sessionVars['productNumber'] == '1' || sessionVars['productNumber'] == '2') and  (sessionVars['quantity'] == null)]" doc:name="Logger"/>
        <!-- true -->

        <logger level="INFO" message="#[(sessionVars['quantity'] == null) and (sessionVars['productNumber'] == '1' || sessionVars['productNumber'] == '2')]" doc:name="Logger"/>
        <!-- true -->

        <message-properties-transformer overwrite="true" scope="session" doc:name="Message Properties">
              <add-message-property key="productNumber" value="3" />
        </message-properties-transformer>

        <logger level="INFO" message="#[(sessionVars['productNumber'] == '1' || sessionVars['productNumber'] == '2') and  (sessionVars['quantity'] == null)]" doc:name="Logger"/>
        <!-- false -->

        <logger level="INFO" message="#[(sessionVars['quantity'] == null) and (sessionVars['productNumber'] == '1' || sessionVars['productNumber'] == '2')]" doc:name="Logger"/>
        <!-- true? it should not be true! -->        
    </flow>
</mule>

score 2 · Answer 1 · answered Nov 09 '14 at 06:17

use &ampamp; instead of and. it calculates the correct value. updated flow

<logger level="INFO" message="#[(sessionVars['productNumber'] == '1' || sessionVars['productNumber'] == '2') &amp;&amp;  (sessionVars['quantity'] == null)]" doc:name="Logger"/>
    <!-- false -->


<logger level="INFO" message="#[(sessionVars['quantity'] == null) &amp;&amp; (sessionVars['productNumber'] == '1' || sessionVars['productNumber'] == '1')]" doc:name="Logger"/>

score 0 · Answer 2 · answered Oct 29 '13 at 17:45

I have no idea why this happens, but I have the same experience in 3.4.0 CE. One workaround to achieve the correct result seems to be to use "&&", as in

#[(sessionVars['quantity'] == null) && (sessionVars['productNumber'] == '1' || sessionVars['productNumber'] == '2')]

MEL logical AND acting weird, order of operands matters?

2 Answers2