You just need to write a class that fits the columns in your data model. You can then give this class to Astyanax in your mutations or queries.
For example, if you had a data model like this
CREATE TABLE fishblogs (
userid varchar,
when timestamp,
fishtype varchar,
blog varchar,
image blob,
PRIMARY KEY (userid, when, fishtype)
);
you would create a class like this:
public class FishBlog {
@Component(ordinal = 0)
public long when;
@Component(ordinal = 1)
public String fishtype;
@Component(ordinal = 2)
public String field;
public FishBlog() {
}
}
When and fishtype form your composite column key and are represented by the FishBlog class. Userid would be your row/partition key and can be of the simple "string" type.
Have a look at this blog explaining in great detail how to insert data with composite keys (where I took this example from).
Hope that helps.