To distinguish between Nominative/Accusative, Partitive/Dative, and Genitive/Locative, the article or adjective is inflected.  If there is no article or adjective, context will tell you what the case is.  (For example, the direct object of a sentence always follows the subject, the partitive will be followed by the plural indefinite article, indicating "some" or "any", and the locative will have a preposition.)