DML operations in the Apex callback method

Question

An apex method that returns a continuation object can’t perform DML. The solution given by the Salesforce developer documentation is the “perform DML operations in the Apex callback method”. https://developer.salesforce.com/docs/atlas.en-us.lightning.meta/lightning/apex_continuations_limits.htm

I tried to do DML operations in the Apex callback method in new Continuation approach. But it was not working. Continuation was failed. It gave below error. What should I do for this?

public with sharing class newContinuation1 {
    private static final String LONG_RUNNING_SERVICE_URL =
        'http://dummy.restapiexample.com/api/v1/employees';
    public static List<String> requestLabel;
    public static String result; 

    @AuraEnabled(continuation=true cacheable=false)
    public static Object getstartRequest() {
        Continuation con = new Continuation(40);
        con.continuationMethod='processResponse';
        con.state='SUCCESS';
        HttpRequest req = new HttpRequest();
        req.setMethod('GET');
        req.setEndpoint(LONG_RUNNING_SERVICE_URL);
        con.addHttpRequest(req);        
        return con;
    }

    @AuraEnabled(cacheable=false)
    public static Object processResponse(List<String> labels, Object state) {

        HttpResponse response = Continuation.getResponse(labels[0]);

        String result = response.getBody();
        Account acct1 = new Account(Name='samushika333');
        try
        {
            insert acct1;
            return result;
        } catch (DmlException e) {
            System.debug('Exception'+e);
            return result;
        }

    }

}

Answer 1

I found a working solution for doing DML from a continuation method. According to the documentation for Continuation Limits,

An Apex method that returns a Continuation object can’t perform Data Manipulation Language (DML) operations.

What I did to get DML to work from a continuation call was to execute another apex method in the same Javascript method that the Apex action / continuation call originated. To get the records that I need to perform DML manipulation on, I just passed the data that was return from the continuation method to the apex method that handles DML.

Here the Javascript class method:

import startRequest from '@salesforce/apexContinuation/CalloutHandler.startRequest';
import insertRecords from '@salesforce/apex/CalloutHandler.insertRecords';

    startRequest() {

        this.loaded = true;
        this.result = '';

        startRequest({objId: this.recordId, someId: this.Some_Id__c})
            .then(result => {

                this.result = result;
                var parsedVal = JSON.parse(result);

                this.sObjectWrapperData = parsedVal.sObjectWrapperData;
                insertRecords({Data: JSON.stringify(this.sObjectWrapperData)});

                this.loaded = false;

            })
            .catch(error => {
                this.error = error;
            });

    }

This is the Apex class methods:

/*
 * Continuation method for POST request
 * */
@AuraEnabled(cacheable=true)
public static Object processResponse(List<String> labels) {

    Wrapper.ResponseWrapper Response = new Wrapper.ResponseWrapper();
    HttpResponse response = Continuation.getResponse(labels[0]);

    if(response.getBody() != null && response.getStatusCode() == 200) {
        Response.sObjectWrapperData = (Wrapper.sObjectWrapper)json.deserialize(response.getBody(),Wrapper.sObjectWrapper.class);
    }

    return json.serialize(Response);
}

/*
 * Method for handling all DML operations data
 * */
@AuraEnabled
public static String insertRecords(String Data) {

    Wrapper.ResponseWrapper Response = new Wrapper.ResponseWrapper();
    Response.sObjectWrapperData = (Wrapper.sObjectWrapper)json.deserialize(Data, Wrapper.sObjectWrapper.class);

    // List of Opportunity records to be updated or inserted.
    List<Opportunity> oppToUpsert = new List<Opportunity>();

            Opportunity o = new Opportunity();
            o.Name = 'Some Name';
            o.AccountId = 'someaccountID';
            o.CloseDate = date.today();
        }
    }

    if (!oppToUpsert .isEmpty())
        Database.upsert(oppToUpsert , false);

    return null;
}

Answer 2

We had the same issue for an LWC we had created, turned out it was not due to the Continuation it was because we had used the @wire service to make the call. I am guessing the @wire service forces Cacheable on which bans DMLs.

Solution, we changed the calling point to be in the connectedCallback and it allowed the DML.