Apex class call from LWC

Question

When you want to call Apex class in visualforce page we have to declare our apex class in the following format.

<apex:page Controller="ClassName">

Whenever we call a visualforce page in which controller attribute is defined it will first create an object for the apex class which is defined in the controller.

I want to do the same in LWC how to do it?

Answer 1

LWC can only invoke static Apex methods, via @wire and imperative calls. There's no instantiation of a "controller" - indeed, there is no "controller" for the LWC, just a (possibly distributed, possibly in one class) set of @AuraEnabled static methods for the LWC to invoke.

Wires are invoked shortly after component instantiation though this is delayed based on any parameters - the wire is invoked once all parameters have defined values. Imperatives are explicitly called from functions in your LWC.

The LWC doesn't rely on state "on the server side" and so must maintain and explicitly pass all required details to each wire or imperative call.

This is covered quite well in the documentation. Note also the "lifecycle hooks". You can also undertake the trailheads to find out more.

If you have code that you wish to share between a Visualforce page and an LWC you will need to refactor the code so it can be called through, or as, an @AuraEnabled static method and from your Visualforce controller.

Also understand that there is no automatically maintained "page state" shared between client and server in LWC (unlike Visualforce). Instead any state must be explicitly passed as parameters to the apex method, and explicitly updated on the client side on receipt of the responses from these calls. This makes for much more responsive pages.

Answer 2

If you want to call Apex on component loading then use the below code

@wire(fetchConRec, ({contactId: '$conId'})) 
 wiredRecord({error,data}) {
 if (data) {
   console.log(data);
 } else if (error) {
     console.log(error);
  }
}

otherwise

fetchConRec(contactId: this.conId)
 .then(result=> {
        console.log('result-->',result);
  })
 .catch(error => {
        console.log('error-->',error);
  });

contactId is Apex class method's parameter conId is JS file variable name

Answer 3

I'm having the same case where I want to access an instance of Apex controller class in LWC. Here's how I did it:

In apex code

@AuraEnabled
    public static YourController getController() {
        return new YourController (true);
    }

In javascript code

import getController from "@salesforce/apex/YourController.getController";

controller;

async connectedCallback() {
  this.controller = await getController();
}

Hope it helps.