What you can do to store a complex json object in a C* skinny row is to
serialize each field independently as a Json String and store each field as
a C* column within the same row (representing a JSON object).
So using the example you mentioned, you could store it in cassandra as:
ColumnFamily["objectKey"]["readings"] = "[{reading1}, {reading2},
{reading3}]"
ColumnFamily["objectKey"]["events"] = "[{event1}, {event2}, {event3}]"
But in fact, that isn't an optimal way to store such data in cassandra,
since you would need to de-serialize all the readings if you were
interested in a particular reading or time period.
A better way to store time series data is to store one measurement/event
per column, so you're able to retrieve data for a particular time period
more easily (since columns are stored in sorted order). One way to do that
for your data would be to store them in 2 column families, as in:
Reading["objectKey"]["timestamp3"] = "{reading3}"
Reading["objectKey"]["timestamp2"] = "{reading2}"
Reading["objectKey"]["timestamp1"] = "{reading1}"
Event["objectKey"]["timestamp3"] = "{event3}"
Event["objectKey"]["timestamp2"] = "{event2}"
Event["objectKey"]["timestamp1"] = "{event1}"
So you're able to reconstruct the original JSON "objectKey" by fetching the
columns from Reading["objectKey"] and Event["objectKey"], and you're also
able to efficiently query all readings between timestamp2 and timestamp3
that ocurred inside the json object, if necessary.
In this post you can find more information on how to store time series data
in C* in an efficient way:
http://www.datastax.com/dev/blog/advanced-time-series-with-cassandra
2013/9/11 Edward Capriolo <edlinuxg...@gmail.com>
> I was playing a while back with the concept of storing JSON into cassandra
> columns in a sortable way.
>
> Warning: This is kinda just a cool idea, I never productionized it.
> https://github.com/edwardcapriolo/Cassandra-AnyType
>
>
>
> On Wed, Sep 11, 2013 at 2:26 PM, Hartzman, Leslie <
> leslie.d.hartz...@medtronic.com> wrote:
>
>> Hi,****
>>
>> ** **
>>
>> What would be the recommended way to deal with a complex JSON structure,
>> short of storing the whole JSON as a value to a column? What options are
>> there to store dynamic data like this?****
>>
>> ** **
>>
>> e.g.,****
>>
>> ** **
>>
>> {****
>>
>> “ readings”: [****
>>
>> {****
>>
>> “value” : 20,****
>>
>> “rate_of_change” : 0.05,****
>>
>> “timestamp” : 1378686742465****
>>
>> },****
>>
>> {****
>>
>> “value” : 22,****
>>
>> “rate_of_change” : 0.05,****
>>
>> “timestamp” : 1378686742466****
>>
>> },****
>>
>> {****
>>
>> “value” : 21,****
>>
>> “rate_of_change” : 0.05,****
>>
>> “timestamp” : 1378686742467****
>>
>> }****
>>
>> ],****
>>
>> “events” : [****
>>
>> {****
>>
>> “type” : “direction_change”,****
>>
>> “version” : 0.1,****
>>
>> “timestamp”: 1378686742465****
>>
>> “data” : {****
>>
>> “units” : “miles”,****
>>
>> “direction” : “NW”,****
>>
>> “offset” : 23****
>>
>> }****
>>
>> },****
>>
>> {****
>>
>> “type” : “altitude_change”,****
>>
>> “version” : 0.1,****
>>
>> “timestamp”: 1378686742465****
>>
>> “data” : {****
>>
>> “rate”: 0.2,****
>>
>> “duration” : 18923****
>>
>> }****
>>
>> }****
>>
>> ]****
>>
>> }****
>>
>> ** **
>>
>> ****
>>
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>
--
Paulo Ricardo
--
European Master in Distributed Computing***
Royal Institute of Technology - KTH
*
*Instituto Superior Técnico - IST*
*http://paulormg.com*
