如何创建无价值的列在Cassandra中通过CQLEngine

Question

I have a question about how I can Create valueless column in Cassandra by CQLEngine. I mean I want store information in column name instead of column value for some purpose. But in CqlEngine you should define you column name before you run your project in model file. Thanks for any help.

Answer 1

What your asking about would traditionally be accomplished using the Thrift api and wide rows, defining your own column names. This is not how CQL3 works. If you want to work this way, you can use pycassa, or you can create columns with compound keys.

For example, with CQL3:

create table ratings ( user_id uuid, item_id uuid, rating int, primary key (user_id, item_id));

You'd actually create a wide row, with user_id as the key, and the columns would have the item_id, and the rating would be the value. With compound primary keys, rows are transposed into columns.

You might want to read this: http://brianoneill.blogspot.com/2012/09/composite-keys-connecting-dots-between.html

Answer 2

Ok, first I need to define my column family like this: create table test( user text, itemLiked text, primary key (user,itemLiked))

so the user is row key and itemLiked is Clustering key. If I insert values to this cf , cassanndra doesn't create row (internally) for that and the itemliked value will be the name of columns insert into test(user , itemLiked) values ( "user1","Item1"); insert into test(user , itemLiked) values ( "user1","Item1");

So cassandra will create two column with name Item1 and Item2 for rowkey user1 this columns hav not any values and as described in this article: http://cassandra.apache.org/doc/cql3/CQL.html in line that: Moreover, a table must define at least one column that is not part of the PRIMARY KEY as a row exists in Cassandra only if it contains at least one value for one such column.