One really cool feature of Liferay JSON web services is the ability to nest service calls.

For example, what if you would like to update a web content journal article via JSON? The /journalarticle/update-article method requires the following four parameters: 

groupId, articleId, and content are easy to come up with. But how can I find the article version number? I could make a separate call to get-article to retrieve the article metadata including the version number, but this would add extra complexity (and an extra network call) to my client code. 

Instead it is also possible to automatically look up the version number while updating with a nested call like this: 

 var cmd = {
            "$article = /journalarticle/get-article": {
                "groupId": article.groupId,
                "articleId": article.articleId,
                "$update = /journalarticle/update-article": {
                    "@version": "$article.version",
                    "groupId": article.groupId,
                    "articleId": article.articleId,
                    "content": xml,
                    "serviceContext.scopeGroupId": article.groupId
                }
            }
        };

How cool!