Render metadata for pagination from Grails RestfulController index/search actions

Question

I am looking for best practices / solution to make \'respond\' method generate extra metadata in the resulting json along with the collection of entities got from DB.

Answer 1

Based on ideas from

http://mrhaki.blogspot.com/2013/12/grails-goodness-rendering-partial.html

http://groovyc.net/non-trivial-restful-apis-in-grails-part-2/

1. Creat a custom CollectionRenderer e.g., SumoJsonCollectionRenderer.groovy

---

import grails.converters.JSON
import grails.rest.render.RenderContext

import grails.rest.render.json.JsonCollectionRenderer
import org.codehaus.groovy.grails.web.mime.MimeType

import groovy.transform.CompileStatic
import static groovy.transform.TypeCheckingMode.SKIP

@CompileStatic
class SumoJsonCollectionRenderer extends JsonCollectionRenderer{

    SumoJsonCollectionRenderer(Class componentType) {
        super(componentType)
    }

    public SumoJsonCollectionRenderer(Class componentType, MimeType... mimeTypes) {
        super(componentType, mimeTypes)
    }

    @CompileStatic(SKIP)
    @Override
    protected void renderJson(object, RenderContext context) {
        log.debug(object)
        log.debug(object.size())
        log.debug(object.getTotalCount())
        Map tObject = ['results':object]
        if(context.arguments?.metadata) {
            tObject['metadata'] = context.arguments.metadata
        }
        super.renderJson(tObject,context)
    }
}

register custom CollectionRenderer at resource.groovy

---

for (domainClass in grailsApplication.domainClasses) {
    "json${domainClass.shortName}CollectionRenderer"(SumoJsonCollectionRenderer, domainClass.clazz)
    "json${domainClass.shortName}Renderer"(JsonRenderer, domainClass.clazz)
    "hal${domainClass.shortName}CollectionRenderer"(HalJsonCollectionRenderer, domainClass.clazz)
    "hal${domainClass.shortName}Renderer"(HalJsonRenderer, domainClass.clazz)
}

Request/Response

---

http://api.mydomain.com:8080/ApiApp/drugs.json?max=5&fields=ndc,id

{"results":[{"id":1,"ndc":"000020803031"},{"id":2,"ndc":"000021200011"},{"id":3,"ndc":"000021407011"},{"id":4,"ndc":"000021975901"},{"id":5,"ndc":"000023004751"}],"metadata":{"total":851,"psize":5,"offset":0}}