System.calloutException: You have uncommitted work pending. CallOut+Asynchrnous DML + Callout

Question

I went through some questions here like System.CalloutException: You have uncommitted work pending which provide answer where the callout can be split into asynchronous way.

Based on the information in below URL, https://help.salesforce.com/articleView?id=000079772&type=1

callout
insert
callout  <---- fails here

I am doing below:

callout
insert (this insert is based on response from first callout, response is being used in second callout and response also gets upserted in custom object in FUTURE method)
callout

Above scenario fails even though I am trying to split the insert operation into a Future/ Queueable method. I cannot have the second callout happening in asynchronous way as the response of second callout should be presented in UI

UseCase: 1) Callout - Retrieve accesstoken - valid for next 5 hours, so u want to reuse this 2) DML - Insert the accesstoken in custom object for reusing 3) Callout - Use the retrieved access token to get the actual response and pass to UI

When my method finds there is a valid active token in database, it is going to skip step 1 from above and proceed to Step 2 and 3. This scenario works perfectly.

It fails when there is no active token found and it has to begin from Step 1.

Any suggestions ?

Answer 1

Splitting the insert operation into a Future/Queueable method is (believe it or not!) actually performing an insert... an insert into the queue!

To solve your problem, do your first callout and the insert in the same transaction, then do your second callout in a Future/Queueable method.

The way I remember and avoid the dreaded "uncommited work pending" exception is for any given transaction, we have to do ALL the callouts first, followed by any DML (or queueing!) operation.

Answer 2

Refer my blog post Visualforce webservice callout synchronously & asynchronously

If you want to achieve as follows and want to display the response of the 2nd callout on UI, without using Future/Queueable method then here is the approach.

callout
insert
callout

Approach

Create a Visualforce and command button action will call FirstCalloutAndSave method to perform callout and DML operation.

Then oncomplete method will perform perform2ndCallOut calling submit method (in a separate transaction) and results of the 2nd callout will be displayed on UI.

<apex:page id="MyVisualforcePage" controller="myExampleController"  showHeader="false">
    <apex:pageMessages id="msgId"/>
    <script>
        function performSecondCallOutMethod()
        {
             perform2ndCallOut();
        }
    </script>
    <apex:form id="myForm">
        <apex:actionFunction name="perform2ndCallOut" action="{!submit}" reRender="script-block,msgId"/>
        <!--fields on the UI -->
        <apex:commandButton value="Save" action="{!FirstCalloutAndSave}"
             oncomplete="return performSecondCallOutMethod();" reRender="msgId"/>
    </apex:form> 
</apex:page>

Controller

public class MyController
{

    public PageReference FirstCalloutAndSave()
    { 
         //1. perform firstout
         //2. perform DML
    }

    public PageReference submit()
    {
        try
        { 
           //perform 2ndCallout and show the result in the visualfore page
           return null
        }
        catch (Exception ex)
        {
           System.debug('Error in submit ' + ex);
                                ApexPages.Message msg = new ApexPages.Message(ApexPages.Severity.Error, ex.getMessage());
                                ApexPages.addMessage(msg);
                                return null;
        }
    }
}