If you don’t have a dog with long hair, but actually dream of one, it could be a reference to yourself. The dog with long hair could be an expression of what is suggested for you; that you should keep long hair.
In your dream, the dog has long hair, to allow you to get up close and personal with it. You get to see what it is like with long hair. This aims to persuade you to keep long hair.
Another interpretation could be a suggestion to you to actually get a dog with long hair/ fur.
