Per the docs,
If you choose lead, you'll see Id, email Address, and any custom fields in the list.
Only string field types are supported in the link field.
So you'll need to either use the Marketo-assigned lead ID or create a new custom string field as your link. I would definitely recommend using the lead ID (which is guaranteed unique) instead of a field like first name or last name, which is not guaranteed to be unique and so is not suitable to be a link field.
You could also create your own unique ID field as a string and populate with an ID from an external system if that works better.
The main thing is that when you insert a custom object record, the link field needs to be populated with a unique primary key that will let Marketo know which lead record to attach it to.
Justin Norris | Perkuto
Thanks for the doc link, but unfortunately I've read through it previously and wasn't much help in explaining why these two lead object fields are missing from the link field list for the "lead" link type.
Both fields are string types, and both a part of the lead object, but doesn't show up in the drop down menu when trying to select a Link field. Is my understanding incorrect and that first/last name are no considered a part of "any custom fields in the list." mentioned in the documentation?
RE: linking to unique ids and fields. I agree is the better route, unfortunately it's not quite a option for us in this case. Our data lives separately (and in this case, incomplete) we were hoping to use Marketo to join our two data sources together while relying on less than ideal join criteria. Our custom object would be keyed off of first and last name combined.
We're looking to supplement our contact records with the additional meta data in this new custom object, which is unique per first/last name. Joining that to our contacts is a many-to-one relationship unfortunately due to legacy dupes. But I can't seem to even get started without being able to link the custom object on first/last name.
Hi Jerry Yi,
The reason First Name and Last Name don't show up in the list is that they are standard fields not custom - that's going to be the blocker here. (Even if you could use them, you need to use a single field for the link, not two combined.)
You will need to use a different field unfortunately.
Justin Norris | Perkuto