I've just had a crash course of Cassandra over the last week and went from Thrift API to CQL to grokking SuperColumns to learning I shouldn't use them and user Composite Keys instead.
I'm now trying out CQL3 and it would appear that I can no longer insert into columns that are not defined in the schema, or see those columns in a select *
Am I missing some option to enable this in CQL3 or does it expect me to define every column in the schema (defeating the purpose of wide, flexible rows, imho).
Yes, CQL3 does require columns to be declared before used.
But, you can do as many ALTERs as you want, no locking or performance hit is entailed.
That said, most of the places that you'd use "dynamic columns" in earlier C* versions are better served by a Map in C* 1.2.
I suggest you to explore composite columns with "WITH COMPACT STORAGE". A "COMPACT STORAGE" column family allows you to practically only define key columns:
Example:
CREATE TABLE entities_cargo ( entity_id ascii, item_id ascii, qt ascii, PRIMARY KEY (entity_id, item_id) ) WITH COMPACT STORAGE
Actually, when you insert different values from itemid, you dont add a row with entity_id,item_id and qt, but you add a column with name (item_id content) and value (qt content). So:
insert into entities_cargo (entity_id,item_id,qt) values(100,'oggetto 1',3);
insert into entities_cargo (entity_id,item_id,qt) values(100,'oggetto 2',3);
Now, here is how you see this rows in CQL3:
cqlsh:goh_master> select * from entities_cargo where entity_id = 100;
entity_id | item_id | qt
-----------+-----------+----
100 | oggetto 1 | 3 100 | oggetto 2 | 3
And how they are if you check tnem from cli:
[default@goh_master] get entities_cargo[100];
=> (column=oggetto 1, value=3, timestamp=1349853780838000)
=> (column=oggetto 2, value=3, timestamp=1349853784172000)
Returned 2 results.
You can access a single column with
select * from entities_cargo where entity_id = 100 and item_id = 'oggetto 1';
Hope it helps
Cassandra still allows using wide rows. This answer references that DataStax blog entry, written after the question was asked, which details the links between CQL and the underlying architecture.
A dynamic column family defined through Thrift with the following command (notice there is no column-specific metadata):
create column family clicks
with key_validation_class = UTF8Type
and comparator = DateType
and default_validation_class = UTF8Type
Here is the exact equivalent in CQL:
CREATE TABLE clicks (
key text,
column1 timestamp,
value text,
PRIMARY KEY (key, column1)
) WITH COMPACT STORAGE
Both of these commands create a wide-row column family that stores records ordered by date.
In addition, CQL provides the ability to assign labels to the row id, column and value elements to indicate what is being stored. The following, alternative way of defining this same structure in CQL, highlights this feature on DataStax's example - a column family used for storing users' clicks on a website, ordered by time:
CREATE TABLE clicks (
user_id text,
time timestamp,
url text,
PRIMARY KEY (user_id, time)
) WITH COMPACT STORAGE
Notes
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