gistfile1.groovy

package examples.answers

// https://answers.atlassian.com/questions/319646/customfield-id-for-scripted-fields?page=1#comment-319992

import com.atlassian.jira.component.ComponentAccessor
import com.atlassian.jira.issue.Issue
import com.atlassian.jira.issue.fields.CustomField
import com.atlassian.jira.issue.CustomFieldManager
import com.atlassian.jira.issue.link.IssueLink
import com.atlassian.jira.issue.link.IssueLinkManager

double childHours = 0;
CustomFieldManager customFieldManager = ComponentAccessor.getCustomFieldManager();
CustomField childField1 = customFieldManager.getCustomFieldObjectByName("Num Scripted Field");
IssueLinkManager issueLinkManager = ComponentAccessor.getIssueLinkManager();

Issue issue = issue

for (IssueLink issueLink : issueLinkManager.getOutwardLinks(issue.getId()))
{
    if( issueLink.getIssueLinkType().name == "Relates")
    {
        double childFieldValue = issueLink.getDestinationObject().getCustomFieldValue(childField1);
        if( childFieldValue != null)
        {
            childHours += childFieldValue;
        }
        else
        {
            childHours += 0;
        }
    }
}

childHours