HTTP callout from trigger [duplicate]

Question

I have the following setup

Object : CurrencyConversion__c

Field : Input_Currency__c

Field : Convert_Currency__c

I want to invoke a callout to an external webservice via a trigger (before inserting a record) in the above custom object.

I will pass "Input_Currency__c" as parameter (Id will not be passed) and the HTTP Response will contain value for "Convert_Currency__c" which I will stamp it back.

Since this webservice will be asynchronous how am I to identify the same record for which this callout was made by the time I get the response from the webservice ?

Answer 1

You can make a callout from the apex trigger and based on the response received you can deserialize and map it to the corresponding fields on the object to update. But make sure you might get the recursion issue inorder to update.

Trigger:

trigger CurrencyConversionUpdate on CurrencyConversion__c (before insert,before update) {
for (CurrencyConversion__c cc : Trigger.new) {
   if (any condition) {
       CurrencyCoversioncall.Integrationccupdate(cc.Id);
       System.debug('cc.Id');
     }
   }

HTTP Class to POST To an External URL:

global class CurrencyCoversioncall {
@future (callout=true)
 public static void Integrationccupdate(id ccid) {
   //Construct HTTP request and response
    //Http request method,Endpoint and setBody
    HttpRequest req = new HttpRequest();
    req.setHeader('Content-Type','application/json');
    String endpoint = 'Endpoint URL FOR External service';
    req.setMethod('POST');
    req.setEndpoint(endpoint); 
    system.debug('CC ID' +ccid);
    //SOQL to construct JSON string in set body
    CurrencyConversion__c cc=[select id,Name, Input_Currency__c from CurrencyConversion__c where id=:ccid];
    system.debug('without pretty'+JSON.serialize(cc));
    String JsonString=JSON.serialize(cc);
    req.setBody(JsonString);
    system.debug(JsonString);
    //Http response method 
    Http http = new Http();
    HTTPResponse res = http.send(req);
    System.debug(res.getBody());

  }
}

Answer 2

You do it in an after insert, passing the ID of the record to the async method. Then make call out to webservice and update the record using the ID you passed in and the results from the webservice