Dynamic Column Families

[Yodit Stanton]

Is there any way in Cassaforte of creating Dynamic column families?  If we take the example given in the Cassandra documentation of a user subscribing to a number of blog posts.  Can I get a general idea of how I model this table in Cassaforte? 

Pic, below of the data model from the cassandra docs.

Many Thanks,


Yodit

[Yodit Stanton]

Ok reading the documentation some more I can see how to create the dynamic tables.  I am not clear though how a normal insert statement would not add a row to the table instead of a column?

[Oleksandr Petrov]

Hi Yodit,

So called dynamic tables are actually virtual entities. I suppose that the article you're referring to is using Thrift interface, where it may have

been a bit less obvious that dynamic tables, or wide rows don't represent a physical entry, and their structure is only imposed by the cassandra 

data model.

Here's an example: http://clojurecassandra.info/articles/data_modelling.html#toc_3 

If you create a table with 

CREATE TABLE movies (title varchar, rating int, time timestamp, PRIMARY KEY (title, time));

You can see that `timestamp` is something that will become a "key" of your dynamic table, and "rating" here will become a "value"

Difference between "row" and "column" in your question lays in a partition key: if "title" field, which is a partition key (which may be composite),

if the partition key is new (haven't been in your DB just yet), you'll have a new row inserted. If it is something that was already there, a new column

will be inserted into an existing row. Cassandra identifies it by the second part of the PRIMARY KEY (time in this case).

Via CQL you'll see it as a plain table of "title" (which will be repeated for many records), rating and timestamp though. 

You can dig deeper into Cassandra data model yourself by using Cassandra-cli: http://clojurecassandra.info/articles/troubleshooting.html#toc_4

Which can show you which records are stored in the same row.

In order to make a transposition, you can use a little utility function we wrote, here's an example:

https://github.com/clojurewerkz/cassaforte/blob/master/test/clojurewerkz/cassaforte/utils_test.clj#L10-L30

I'll cover it in docs, since just found out it's not yet covered there.

Hope that helps.

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alex p

[Yodit Stanton]

Thanks Alex!  That was helpful, I have managed to create the tables as I wanted.

Regards,


Yodit