Writers...a question regarding dialects in dialogue

Do you a) write the actual way the dialect would be written or sound within the dialogue or do you b) just state prior to the dialogue that the character is either Creole, Irish, etc.  One of my characters is a local New Orlenian/Creole woman and I wanted to bring this across.  But what is the appropriate way for a reader to grasp this concept.
Thank you for any guidance and/or clarification. Robin