E0109: A field reference names no field

Post.Title written as a value is a field reference: a typed handle on the field, used by queries and validation. The type has no field of that name, the field is ambiguous (two embedded structs have it), or it is unexported in another package.

Wrong

type Post struct{ Title string }

var byTitle = Post.Titel

Right

type Post struct{ Title string }

var byTitle = Post.Title