Usage of @Via in sling models

[Nitiks25]

I understand from the documentation, that @Via is used to inject objects not available through the adaptable mapped to the model

In that case, if my adaptable is Resource.class and I have to inject SlingHttpServletRequset or SlingHttpServletResponse. I will have to use @Inject @Via to fetch it from SlingHttpServletRequest adaptable?

In that case, what is the parameter I have to pass to @Via?

In case of resource, it will be @Via ("resource") - what will it be for slingRequest?

[smacdonald2008]

This annotation is well explained in this topic:

Apache Sling :: Sling Models

There are some code examples too.

[Nitiks25]

Thanks Smacdonald,

From that page it is clear what the Via Type does i.e choose a different adaptable for a particular injection. It's also given an example of how to set Resource as the adaptable for an Injection if the adaptable model is sling request:

@Inject @Via("resource")

     String getPropertyName();

But what if the model level adaptable is 'Resource' and I need to choose request as the adaptable for an Injection? that's not given on that page. Is that even possible? Tried @Inject @Via("request")  and other similar parameters but it doesn't work.

[VeenaVikraman · Accepted solution]

Nitik,

  Let me try to explain you what I understand here . Let us take the simple example from what documentation Scott has shared

  - So this says ; when the model's adaptable is SlingHttpServletRequest , then when you try to inject getPropertyName() ; it will be return the property via resource method of the SlingHttpServletRequest object "request" like the below

request.getResource().getValueMap().get("propertyName", String.class)

That said , if you check the API SlingHttpServletRequest (Apache Sling Aggregate 5-incubator API)  you can understand that a resource can be fetched from a request , but the vice versa is not possible .

    So basically that means inject the value via resource API in SlingHttpServletRequest API.

  I am not aware of a way to get a request object from a resource and hence I don't believe something like below is even possible

@Model(adaptables=Resource.class)

public class MyModel { 

    @Inject

    @Via("request")

    private String someObj;

}

For further reading the below section explains what all standard types are provided via while and how it is implemented

Apache Sling :: Sling Models

The other thing you can do is to adapt the SlingHttpServletRequest and get the resource from it

@Model(adaptables = SlingHttpServletRequest.class)
public class MyModel {
     @Inject
     SlingHttpServletRequest request;
     @PostConstruct
     protected void init() {
         Resource resource = request.getResource() ;
     }
}

[Nitiks25]

Thanks a lot Veena. Makes sense now. But I want clarification on one thing: I have the model adaptable as Resource. And I have injected slinghttpservletresponse object using just an @Inject i.e.

@Inject

SlingHttpServletResponse response

and a valid response object is being returned. As per documentation, this isn't supposed to happen since response object is only supposed to be available if model is set to sling request as adaptalbe

I'm just wondering, how it is working then?

[BrijeshYadav]

Hi,

I think you should use @SlingObject injector. like below
@Model(adaptables = Resource.class)

public class ResourceExampleModel {

  @SlingObject

   private SlingHttpServletRequest request;

}

As par the documentation also @SlingObject injects commonly used sling objects if the field matches with the class: request, response, resource resolver, current resource, SlingScriptHelper
Apache Sling :: Sling Models

/Brijesh Yadav

[VeenaVikraman]

I have not tried injecting a response object . but I will surely give it a try and get back to you.

[Former Community Member]

for sling request it will be:

@Self

SlingHttpServletRequest  request;

[Nitiks25]

Thanks a lot Veena,

yes, if you could let me know that will help a lot

because as per the documentation injecting response object using @ inject when the adaptable is resource is not suppose to work but it is still working.

[VeenaVikraman]

Yes Nitik. I am wondering how that can be possible. Because you cannot inject a SlingHttpResponse object to a class which is adapted as Resource. The documentations says as below.

@Inject : marks a field or method as injectable - If this is to be believed then your class (which is adapted as a Resource) cannot inject a response object.

I am not sure if anything here make sense at all SlingObject (Apache Sling 8 API)  .

[Nitiks25]

I have tried @slingObject too but intermittently it returns a null response. And from what I understand from the documentation that is also not supposed to work since adaptable is not request. But weirdly @inject is working fine.

[VeenaVikraman]

I would request some expert advice Jörg Hoh​ Feike Visser​

[rajeevy89244319]

I am trying to follow documentation on Customizing Core Components

// get the default implementation for delegating

@Self @Via(resourceType="core/wcm/components/breadcrumb/v2/breadcrumb", type=ResourceSuperType.class)

When I am trying to use resourceType with @Via, I am getting compilation error saying that resourceType attribute is not supported for @via annotation. Has anyone tried this and can assist me with correct dependencies to use this.

Thanks,

Rajeev

[smacdonald2008]

Where does it state that when customizing Core Components - you can use @Via annotation. I want to follow along.

[rajeevy89244319]

It is in customizing the logic section on Customizing Core Components

Below is code snippet provided:

package com.mysite.components.models;

@Model(adaptables = SlingHttpServletRequest.class,

       adapters = Breadcrumb.class,

       resourceType = "my-site/components/breadcrumb")

public class MyCustomBreadcrumbImpl implements Breadcrumb {

    /* ... */

    // get the default implementation for delegating

    @Self @Via(resourceType="core/wcm/components/breadcrumb/v2/breadcrumb", type=ResourceSuperType.class)

    private Breadcrumb delegate;

}

[smacdonald2008]

OK -- I am going to try to do this.

[smacdonald2008]

Problem with this code example in the AEM Docs is its missing import statements. I am adding them and will post back the version that compiles.

[rajeevy89244319]

I have tried with imports but getting error. For @Via, only type and value attributes are allowed. resourceType is invalid attribute. Not sure if it has to dependency bundle version mismatch.

[smacdonald2008]

Yes - doc example looks wrong for sure. I am workign on this one. I am talking to the consulting team to see if we have a good KB articles on this as well. We will log a bug on the docs as @Via does not support what is shown in the docs.

[smacdonald2008]

I got it compiling with @Via

1st - i created a new Maven 13 Archetype project following this article: Creating an Adobe Experience Manager 6.4 Project using Adobe Maven Archetype 13

2nd added the new class to this project;  (NEVER ADD  A CLASS TO THE CORE COMPONENT PROJECT taken from Github). Always extend from a new AEM Java project. Here is full example:

package com.adobe.community.core.models;

import org.apache.sling.models.annotations.injectorspecific.Self;

import org.apache.sling.models.annotations.Via;

import org.apache.sling.api.resource.Resource;

import org.apache.sling.models.annotations.Default;

import org.apache.sling.models.annotations.Model;

import org.apache.sling.settings.SlingSettingsService;

import org.apache.sling.api.SlingHttpServletRequest;

import org.apache.sling.models.annotations.via.ResourceSuperType;

import com.adobe.cq.wcm.core.components.models.Breadcrumb;

@Model(adaptables = SlingHttpServletRequest.class,

       adapters = Breadcrumb.class,

       resourceType = "my-site/components/breadcrumb")

public class MyCustomBreadcrumbImpl implements Breadcrumb {

    /* ... */

    // get the default implementation for delegating

@Self @Via(value="core/wcm/components/breadcrumb/v2/breadcrumb", type=ResourceSuperType.class)

    private Breadcrumb delegate;

}

See:

3rd -add Core Components in POM

<dependency>

        <artifactId>core.wcm.components.core</artifactId>

        <version>2.0.4</version>

        <groupId>com.adobe.cq</groupId>

        <scope>provided</scope>

        </dependency>

(plus the UBER AEM JAR and others discussed in above article)

Finally -- if anyone wants to know more about the @Via annotation - see this Javadoc here - Apache Sling 9 API

[rajeevy89244319]

Thanks Sam. I see.. you changed attribute resourceType to value for @via.. So documentation needs to be updated for correct attribute,