Salesforce: rendering of Visual Force pages and context

Aufrufe: 124

In a simple, straightforward programming situation, you would assume that functions are executed when they are seemingly called. When you are rendering a Visual Force page in Salesforce, things seem to be a bit mixed up. Though it seems counter-intuitive, it is understandable what happens.

Let’s take a simple example of a Visual Force page with a controller.

Page (atest):

<apex:page controller="Atest">
    Parameter: {!parameter} <br />
    Parameter2: {!parameter2} <br />
    Parameter: {!parameter} <br />
    Parameter2: {!parameter2} <br />
    Parameter: {!parameter} <br />
    Parameter2: {!parameter2} <br>
</apex:page>

Controller:

public class Atest {
    private Integer parameter;

    public Atest () {
        System.debug ('Constructor called.');
        parameter = 1;
    }

    public Integer getParameter () {
        System.debug ('getParameter');
        parameter = parameter + 1;
        return parameter;
    }

    public Integer getParameter2 () {
        System.debug ('getParameter2');
        parameter = parameter + 1;
        return parameter;
    }

    public PageReference nextPage () {
        PageReference page1 = new PageReference('/apex/atest2');
        Blob b = page1.getContentAsPDF();
        PageReference page2 = new PageReference('/apex/atest2');  
        b = page2.getContentAsPDF();
        PageReference page3 = new PageReference('/apex/atest2');  
        return page3;
    }
}

{!parameter} is a reference to the method getParameter () and {!parameter2} a reference to getParameter2 (). Ignore the method nextPage () for now…

So what you might expect is that the Visual Force renderer calls getParameter (). This increases the variable parameter by 1 and returns its new value. We do see the output “Parameter: 2” – as expected. Then the renderer calls getParameter2 (). This again increases the variable parameter by 1 and returns its new value. We do see the output “Parameter2: 3” – as expected.

Next, we want “parameter” again – seemingly a call to the method getParameter (). But now the method is not actually executed; parameter is not increased anymore. We get the outputs “Parameter: 2” and “Parameter2: 3” again and again, no matter how many times we think the method is called.

Now for the second part in the controller above, we need the VF page atest2, which is virtually the same, except that it is a different file. Also, for convenience to call the method in our class, add

<apex:form>
    <apex:commandButton action="{!nextPage}" value="next page" />
</apex:form>

to the page atest. When you now click on “next page”, the page atest2 is created 3 times. To make sure that it is actually rendered, we get the content of the page as a pdf, and the third time, the page is returned as a PageReference. Therefore you are transported to the page atest2.

What you now see is “Parameter: 4” and “Parameter2: 5”. Even though we have rendered the page atest2 3 times, the variable parameter has only been increased by 1 two times.

This is because the renderer works in the same context for all 3 times it renders atest2. getParameter () and getParameter2 () are both called exactly once, and that only, because we are rendering a page in a new context – the call to the method nextPage (). You could even create the pages atest3 and atest4, have them rendered after each other (in one method), and “Parameter” and “Parameter2” will be the same value for each rendered page.

Any output of a method is directly cached, and the method is not called again, except for if you force a rerender – because that is what re-rendering is for. If you know that values will change, you have to instruct Visual Force to do a new rendering.

To get around this, make sure that you create a new context for a new page with changing information. The easiest way to do so is IMHO to create a controller instance for every page that needs to be rendered, and this in turn can be done by having a different controller for the subsequent pages.

tl;dr:

Do not change the information of a variable or method during one rendering context. Have all information be calculated before anything is actually rendered, and do not change information when using a get-method. If information changes due to user input, have the sections that show information based on the input rerendered when necessary.

Overall: within one context the VF renderer will always call any getter only once.

Salesforce – Assets with or without Contact and/or Account

Aufrufe: 515

In test classes it is always a good thing if you are not just going through your code, but also to actually test if it is working according to design. To make your test shine, you would test both kinds of cases, working examples as well as those where you expect an error to occur.

To test a trigger, that ensures Contact and Account to be set on an Asset (as long as certain parameters are fulfilled), I added a test case where the trigger could not work properly.

According to the Apex documentation, an Asset must have Contact and/or Account set, otherwise you will run into an Exception (FIELD_INTEGRITY_EXCEPTION: Every asset needs an account, a contact or both).

Screenshot of Asset Object Reference - AccountId must be set

So, my Test class includes

Asset a = new Asset (Name = 'Test asset');
try {
    insert a;
    System.assert (false, 'Should not reach this, an Asset needs an Account or Contact');
}
catch (Exception e) {
}

However, in the project I work at currrently, this assertion fails, as our Assets can exist without neither Contact nor Account.

And this is where the documentation is plainly wrong, as it depends on the Organization-Wide Defaults for sharing. If you set access to anything except the default (Controlled by Parent), you can create Assets without Account or Contact. So the documentation is wrong 75% of the time, as a setting of “Private”, “Public Read Only” and “Public Read/Write” allows Assets without.

This was a pitfall for me, as my test class worked on one box, but not on another. And soometimes failing tests hint at an issue with the org itself. But only sometimes, most times it is because a developer did not set up the test correctly.

Salesforce API documentation could be better with API versions

Aufrufe: 139

Once again I found a nice, no, necessary feature. When searching for RecordType-IDs in Apex, you could either query for them with SOQL (burning away the precious number of statements) OR you could just ask the schema.

With List<RecordTypeInfo> contactRTs = Schema.SObjectType.Contact.getRecordTypeInfos() you can get all available RecordTypes for this Object. With contactRTs[0].getName() you can get the label of the record type.

The label. This may be dependent on the language of the user, so it’s utterly useless in code. But there is also contactRTs[0].getDeveloperName() – yay! However, the documentation never states which is the minimum API needed for a function call, and this is absolute crap. Why not just add a line with the API-version? Otherwise you may get errors, which contradict the documentation.

Yes, I know that the Summer`18 release is not far now, so in this case it means that it was a bit more than a week before I can use this needed feature. But it cost me quite some time – checking if I had a typo, if I misread … and then finally a search for the release notes with this function. With the API version in the docs, this would have been a matter of minutes…