Service Component Design Pattern

Lighting Web Components addresses many of the issues this design pattern sought to address, so moving forward I will be maintaining only the lwc-utils repo where you can find LWC specific design patterns (and utility modules) compared side by side with this deprecated aura service component framework.

The Service Component design pattern makes it easy for custom components placed separately from each other (not having any parent-child hierarchy) to easily share a single Apex Controller and reduce redundancy of inter-component communication through key-value events.

Having no component hierarchy makes it more simple to place components anywhere on a lightning page and allowing more flexibility of creating a dynamic user experience out of mixing native and custom components.

Additionally, the Service Component design pattern allows wrapping of base lightning components to provide much more utility than what is currently offered.

tl;dr: Deploy > App Launcher > Service Components

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The service components in this sample app are:

DataService which encapsulates serverside callouts. A single Apex Controller is attributed to this headless component which uses aura:methods to pass parameters to the JS controller which handles serverside configuration like action.setStorable() or action.setParams(). The action will be passed to helper.dispatch() to make the asynchronous callout.

EventService which encapsulates a key-value pair (optional value) model for both application and component events. This component registers and fires generic events which need to be parsed by the handling component(s) via key-value. There is a special recordEvent which is for Lightning Console (since app events broadcast to all console tabs). This can also listen to Platform Events easily and react to them (via lightning:empApi).

MessageService which wraps lightning:overlayLibrary and provides dynamic creation aura:methods for modal bodies and footers.

QuickUpdateService which wraps Lightning Data Service (i.e. force:recordData) and provides an aura:method to very quickly configure a single-object, single-record DML to any sObject. Since this uses LDS, profile security is respected. This is a POC component.

DataTableService which can quickly generate tableData and tableColumns in a format expected by lightning:datatable. It's designed primarily for read-only, single hierarchy tables. It's still possible to perform further processing either serverside or clientside to configure lightning:datatable more granularly. Parent relationship (1 level tested) works and there are helper functions to flatten the data both serverside (column definition) and clientside (data definition).

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DataService Usage Example

Drop this into a component that needs serverside data:

AccountSelector.cmp

<aura:component implements="flexipage:availableForAllPageTypes">
  <c:DataService aura:id="service"/> 
  <aura:handler name="init" value="{! this }" action="{! c.doInit }"/>
</aura:component>

AccountSelectorController.js

doInit: function (component, event, helper) {
  helper.service(component).fetchAccountCombobox(
    $A.getCallback((error, data) => {
      if (data) {
        console.log("data from my apex controller is: "+data);
      }
    })
  );
},

AccountSelectorHelper.js

// ServiceHeaderHelper.js
service : function(component) {
  return component.find("service");
},

EventService Usage Examples

Some samples from the app:

helper.eventService(component).fireAppEvent("ACCOUNT_ID_SELECTED", selectedOptionValue);

helper.eventService(component).fireAppEvent("HEADER_CLEARTABLE");

Handling App, Record, or Comp events with EventService

In any component that needs to listen to these, attach a handler like this:

ContactDatatable.cmp

<aura:handler event="c:ServiceAppEvent" action="{! c.handleApplicationEvent }"/>

ContactDatatableController.js

handleApplicationEvent : function(component, event, helper) {
  let params = event.getParams();
  switch(params.appEventKey) {
    case "ACCOUNT_ID_SELECTED": // fallthrough
    case "CONTACTS_UPDATED":
      helper.loadContactTable(component, params.appEventValue);
      break;
    case "HEADER_CLEARTABLE":
      component.set("v.tableData", null);
      break;
  }
},

Handling Platform Events with EventService

Using v44, we can leverage lightning:empApi to do this:

PlatformEventListener.cmp

<c:EventService aura:id="eventService" 
  channel="/event/Contact_DML__e" 
  onMessage="{! c.handleContactDmlEvent }"/>

PlatformEventListenerController.js

handleContactDmlEvent : function(component, event, helper) {
  let payloadJSON = JSON.stringify(event.getParam("payload"));
  component.set("v.payloadJSON", payloadJSON);
}

MessageService Usage Examples

At its core, this is a wrapper around the lightning:overlayLibrary which provides some helper functionality for creating both the body and the footer. There are some special features:

• Able to handle text or custom component as the modal body.
• Always handles the footer cancel button.
• Specify a main action function which can be either:
  • On the originating component by using component.getReference("someFunction").
  • On the modal component (the body) that's being created by using "c.someFunctionOnTheModalComponent".
• Pass an Object of parameters to the modal component (the body) from the originating component by using object notation while setting up the modal.

When you drop in MessageService.cmp into a component, such as ContactDatatable.cmp, this is an example of how you can open a modal from a function in ContactDatatableController.js.

ContactDatatableController.js

handleOpenComponentModal : function(component, event, helper) {
  let selectedArr = component.find("searchTable").getSelectedRows();

  helper.messageService(component).modal(
    "update-address-modal",                           // auraId
    "Update Address: "+selectedArr.length+" Row(s)",  // headerLabel
    "c:ContactAddressForm",                           // body, MessageService will dynamically create this
    {
      contactList: selectedArr                        // bodyParams, MessageService dynamically passes these to c:ContactAddressForm
    },
    "c.handleUpdateMultiAddress",                     // mainActionReference, see above on where you can feed this
    "Update"                                          // mainActionLabel
  );
},

The above c.handleUpdateMultiAddress is a reference to a function found on ContactAddressForm.cmp. MessageService.cmp is able to grab reference appropriately and wire it up to the Update main action found in the modal footer.

So, even though overlayLibrary modalBody and modalFooter are siblings, the footer is referencing a controller action on the body. This makes it easier to write all your container logic on a modalBody and leverage MessageService.cmp to just open a self-contained modalBody component.

QuickUpdateService Usage Examples

At its core, this is a wrapper around force:recordData which allows for simple single record DML.

This example from ContactDatatable.cmp uses a single button to update multiple fields on a single record. The only attributes QuickUpdateService.cmp expects is a configObject containing the recordId and fieldUpdates properties.

Currently, there is no type checking or much error handling.

ContactDatatableHelper.js

  clearMailingAddressWithLightningDataService : function(component, row) {
    let _self = this;
    let configObject = { // QuickUpdateService only expects this object with recordId and fieldUpdates properties
      recordId: row["Id"],
      fieldUpdates: {
        "MailingStreet": null,
        "MailingCity": null,
        "MailingState": null,
        "MailingPostalCode": null,
        "MailingCountry": null
      }
    }
    _self.quickUpdateService(component).LDS_Update(
      configObject,
      $A.getCallback((saveResult) => {
        switch(saveResult.state.toUpperCase()) {
          case "SUCCESS":
            _self.messageService(component).showToast({
              message: "Cleared Mailing Address.",
              variant: "success"
            });
            _self.loadContactTable(component, row["AccountId"]);
            break;
          case "ERROR":
            _self.messageService(component).showToast({
              title: "Error Clearing Mailing Address",
              message: JSON.stringify(saveResult.error[0].message),
              variant: "error",
              mode: "pester"
            });
            break;
        }
      })
    );
  },

DataTableService Usage Examples

This is a library service component. It's designed to make read-only lightning:datatable very quick to spin up.

This example is from CaseDatatable.cmp (which is actually created inside a modal from ContactDatatable.cmp). The only attributes DataTableService.cmp expects is a tableRequest Object containing the queryString and bindVars properties.

There is no way to fetch the more granular tableColumns specific configurations that are offered from lightning:datatable however it's possible to post-process the tableColumns data even futher serverside OR clientside.

There is simple handling of parent relationships fields.

CaseDatatableController.js

  doInit : function(component, event, helper) {
    let contactRecordId = [].concat(component.get("v.contactRecordId")); // guarantees array for idSet
    if (!$A.util.isEmpty(contactRecordId)) {
      let tableRequest = {
        queryString: "SELECT "
                   + "Id, CaseNumber, CreatedDate, ClosedDate, Description, Comments, Status, Subject, Type, Owner.Name"
                   + "FROM Case "
                   + "WHERE ContactId =: idSet "
                   + "ORDER BY CaseNumber ASC",
        bindVars: {
          idSet: contactRecordId,
        }
      }
      helper.tableService(component).fetchData(
        tableRequest,
        $A.getCallback((error, data) => {
          if (!$A.util.isEmpty(data)) {
            component.set("v.tableData", data.tableData);
            component.set("v.tableColumns", data.tableColumns);
          } else {
            if (!$A.util.isEmpty(error) && error[0].hasOwnProperty("message")) {
              helper.messageService(component).showToast({
                message: error[0].message,
                variant: "error"
              });
            }
          }
        })
      );
    }
  }