Salesforce Webservice Error - web-services

Question

I am receiving the following error from a class that invokes a webservice.
"You have uncommitte​d work pending. Please commit or rollback before calling out"
Here is the class that is calling the webservice:
global class myWS
{
WebService static string invokeExternalWs(string childValue, string parentValue)
{
HttpRequest req = new HttpRequest();
req.setEndpoint('https://externalURL/Services');
req.setMethod('POST');
req.setHeader('Content-Type', 'text/xml; charset=utf-8');
req.setHeader('SOAPAction', 'http://externalService/externalMethod');
string b = '--soap request goes here--';
req.setBody(b);
Http http = new Http();
try {
//Execute web service call here
String xObjectID ='';
HTTPResponse res = http.send(req);
Dom.Document doc = res.getBodyDocument();
String soapNS = 'http://schemas.xmlsoap.org/soap/envelope/';
Dom.XmlNode root = doc.getRootElement();
for(dom.XmlNode node1 : root.getChildElements()) {
for(dom.XmlNode node2 : node1.getChildElements()) {
for(dom.XmlNode node3 : node2.getChildElements()) {
for(dom.XmlNode node4 : node3.getChildElements()) {
xObjectID = node4.getText();
}
}
}
}
return xObjectID;
} catch(System.CalloutException e){
return 'ERROR:' + e;
}
}
}
UPDATE: Here is my class that is executing myWS
public void applyURLString(ID ArgBuildID) {
Builder__c current_build = [SELECT id, name, LLURL__c, column1, column2, Opportunity__c
FROM Builder__c
WHERE id = :ArgBuildID];
if(current_build.LLURL__c == null || current_build.LLURL__c.trim().length() == 0)
{
String tmpFolderName = current_build.column1 + ' - ' + current_build.column2;
String LLWSResultPattern = '[0-9]{2,}';
String myWSXMLResult = myWS.invokeExternalWs(tmpFolderName,'test');
Boolean LLWSPatternMatched = pattern.matches(LLWSResultPattern,myWSXMLResult);
if(LLWSPatternMatched)
{
Opportunity oppt = [SELECT Id,Name
FROM Opportunity
WHERE Id = :current_build.Opportunity__c
LIMIT 1];
oppt.LLURL__c = 'https://someService/' + myWSXMLResult;
update oppt;
}
}
}
UPDATE #2 - Here is where applyURLString() is executed. This is the only place that DML is executed prior to my HTTP request. Yet I need the ID of the new Builder record.
Builder__c insertBuild = new Builder__c();
insertBuild.Opportunity__c = opportunityId;
insertBuild.Product_Group__c = selectedBuild.Product_Group__c;
insertBuild.Manual_Build_Product__c = selectedBuild.Manual_Build_Product__c;
insert insertBuild;
applyURLString(insertBuild.Id);
Any ideas why this error would occur?

Answer 1

#JCD's suggestion to use an #future annotation solved my problem. Thanks again!