A Groovy script to compare the Due Date field against the Resolved Date field. If the Resolved Date is after the Due Date, then the Target Met field would be set to "No". Otherwise, it would be set to "Yes"

ValidateTwoDatesWorkflow.groovy

/**
  * @author jalex
  * @version 1.0
  *
  * A Groovy script to compare the Due Date field against the Resolved Date field. If the Resolved Date is after the
  * Due Date, then the Target Met field would be set to "No". Otherwise, it would be set to "Yes"
  *
  */

import com.atlassian.jira.ComponentManager
import com.atlassian.jira.issue.CustomFieldManager
import com.atlassian.jira.issue.ModifiedValue
import com.atlassian.jira.issue.customfields.manager.OptionsManager
import com.atlassian.jira.issue.customfields.option.Option
import com.atlassian.jira.issue.fields.CustomField
import com.atlassian.jira.issue.fields.layout.field.FieldLayoutItem
import com.atlassian.jira.issue.util.DefaultIssueChangeHolder
import org.apache.log4j.Category
import java.text.SimpleDateFormat

// Logging variables
Category infoLog = Category.getInstance("com.onresolve.jira.groovy.PostFunction")
infoLog.setLevel(org.apache.log4j.Level.INFO)

// Constants declarations
def targetMetFieldName = "Target Met"
Long targetMetYesOptionID = 10001
Long targetMetNoOptionID = 10002

// We grab the related fields here
ComponentManager componentManager = ComponentManager.getInstance()
CustomFieldManager customFieldManager = componentManager.getCustomFieldManager()
CustomField targetMetField = customFieldManager.getCustomFieldObjectByName(targetMetFieldName)
String dueDateValue = issue.getDueDate()
String resolvedDateValue = issue.getResolutionDate()

// Some error checking
if (dueDateValue.equals(null)) {
    infoLog.info "No due date specified for issue ${issue.getKey}"
} else if (resolvedDateValue.equals(null)) {
    infoLog.info "No resolved date specified for issue ${issue.getKey}"
} else if (targetMetField.equals(null)) {
    infoLog.info "Custom field ${targetMetFieldName} does not exist in the instance."
}

// Parsing the Resolved Date and Due Date fields as a Date() object
Date dueDate = new SimpleDateFormat("yyyy-MM-dd").parse(dueDateValue)
Date resolveDate = new SimpleDateFormat("yyyy-MM-dd").parse(resolvedDateValue)

infoLog.info "Due Date for ${issue.getKey()} is ${dueDate.toString()}"
infoLog.info "Resolved Date for ${issue.getKey()} is ${resolveDate.toString()}"

// We grab the available options from the custom field
Object selectValue = issue.getCustomFieldValue(targetMetField) //grab current value for the custom field
FieldLayoutItem fieldLayoutItem = ComponentManager.getInstance().getFieldLayoutManager().getFieldLayout(issue).getFieldLayoutItem(targetMetField)
OptionsManager optionsManager = (OptionsManager) ComponentManager.getComponentInstanceOfType(OptionsManager.class)
Option targetMetNoOption = optionsManager.findByOptionId(targetMetNoOptionID)
Option targetMetYesOption = optionsManager.findByOptionId(targetMetYesOptionID)

if (targetMetNoOption.equals(null)) {
    infoLog.info "There is no option with the ID ${targetMetNoOptionID}"
} else if (targetMetYesOption.equals(null)) {
    infoLog.info "There is no option with the ID ${targetMetYesOptionID}"
}

// Date comparisons go here
if (resolveDate.after(dueDate)) {
    targetMetField.updateValue(fieldLayoutItem, issue, new ModifiedValue(selectValue, targetMetNoOption), new DefaultIssueChangeHolder())
    infoLog.info "Custom field ${targetMetField.getFieldName()} for issue ${issue.getKey()} is set to No"

} else {
    targetMetField.updateValue(fieldLayoutItem, issue, new ModifiedValue(selectValue, targetMetYesOption), new DefaultIssueChangeHolder())
    infoLog.info "Custom field ${targetMetField.getFieldName()} for issue ${issue.getKey()} is set to Yes"
}