Search For Multiple Properties by Value Cassandra - cassandra

Question

How can we design a cassandra model for storing a group say 'Item' having n properties P1,P2...PN and
retrieve the item by searching the item property by value
For Example
Item Item_Type State Country
Item1 Solid State1 Country1
In traditional RDBMS we can issue a select query
select Item from table where Item_Type='Solid' and Country='Country1'
How can we achieve such a model in NoSql Cassandra,we have tried cassandra secondary index but it seems to be not applicable.

Answer 1

For properties P1..PN you will have to ALTER the table as with RDMSs or use an outdated thrift protocol based API (i'd suggest Astyanax for this) which can add columns on-the-fly (but this is considered bad practice). Another possibility is to use a collection of properties where one of your columns is a collection of values:
CREATE TABLE item (
item_id text PRIMARY KEY,
property set<text>
);
For SELECTing values with multiple WHERE clauses you can use secondary indexing or if you know what columns are going to be required in the WHERE clause you can use a composite key, but I would recommend secondary indexes if you are going to have a lot of columns that need to be in the WHERE clause.

Answer 2

The answer to many Cassandra data modelling questions is: denormalize.
You can solve your problem by building indexes yourself. For each property have a row with the property name as key and the values and item ID as columns:
CREATE TABLE item_index (
property TEXT,
value TEXT,
item_id TEXT,
PRIMARY KEY (property, value, item_id)
)
you also need a table for the items:
CREATE TABLE items (
item_id TEXT,
property TEXT,
value TEXT,
PRIMARY KEY (item_id, property)
)
(notice that in the item_index table all three columns are in the primary key, because I assume that multiple items can have the same value for the same property, but in the items table only has item_id and property in the primary key, because I assume that an item can only have one value for a property -- you can solve this for multi-valued properties too, but you have to do a few more things and it will complicate the example)
Every time you insert an item you also insert a row in the item_index table for each property of the item:
INSERT INTO items (item_id, property, value) VALUES ('thing1', 'color', 'blue');
INSERT INTO items (item_id, property, value) VALUES ('thing1', 'shoe_size', '8');
INSERT INTO item_index (property, value, item_id) VALUES ('color', 'blue', 'thing1');
INSERT INTO item_index (property, value, item_id) VALUES ('shoe_size', '8', 'thing1');
(you might want to insert the item as a single BATCH command too)
to find items by shoe size you need to do two queries (sorry, but that's the price you pay for the flexibility -- maybe someone else can come up with a solution that does not require two queries):
SELECT item_id FROM item_index WHERE property = 'shoe_size' AND value = '8';
SELECT * FROM items WHERE item_id = ?;
where the ? is one of the item_ids returned from the first query (because more than one can match, remember).