I want to save a reference to a bRepFace when a user closes and then reopens a document, presumably I could do this by looking up the face based on the component name, body name, and then the tempId.
The documentation here: http://help.autodesk.com/view/fusion360/ENU/?guid=GUID-39FBB1EC-7E58-4A92-AF30-69D080E385ED
says that BrepBody has a function "getEntityFromTempId" but I get an attribute error and can't find it elsewhere in the documentation, does this function exist. If it doesn't can they fix the documentation or (better yet) add the useful function.
Otherwise, what is the best way of saving a reference to a specific BrepFace. I save my structure to a Json file, so it needs to be something that could be parsed from a string essentially.
Thanks for pointing out this problem. I've updated the source of the documentation so it will be available the next time the help is pushed out. The new description says:
Returns the temporary ID of this face. This ID is only good while the document remains open and as long as the owning BRepBody is not modified in any way. The findByTempId method of the BRepBody will return the entity in the body with the given ID.
As you can see, it doesn't do what you want to do. The best solution in your case will be to create an attribute on the face. In this case you would be using attributes to essentially name the face. You can save the name you assigned to the JSON file. You can read more about attributes in the Attributes topic in the API help.