> Consider a course_students col family which gives a list of students for a
> course
I would use two CF's:
Course CF:
* Each row is one course
* Columns are the properties and values of the course
CourseEnrolements CF
* Each row is one course
* Column name is the student ID.
* Column value may be blank or some useful value.
Hope that helps.
-----------------
Aaron Morton
Freelance Developer
@aaronmorton
http://www.thelastpickle.com
On 14/09/2012, at 3:19 PM, Michael Morris <michael.m.mor...@gmail.com> wrote:
> I'm fairly new to Cassandra myself, but had to solve a similar problem. If
> ordering of the student number values is not important to you, you can store
> them as UTF8 values (Ascii would work too, may be a better choice?), and the
> resulting columns would be sorted by the lexical ordering of the numeric
> values (as opposed to numeric sorting), so it would be 1, 10, 11, 2, 3, 31,
> 5...
>
> In my situation, I had a document, composed of digitized images of the pages.
> My row key is the doc id number, and there were document level attributes,
> as well as page level attributes I wanted to capture in the row. So in my
> model, I used composite columns of 3 UTF8 values. The first is an attribute
> descriptor, I used 'a' to indicate a document level attribute, and 'p' as a
> page level attribute. The second composite value depends on the 1st, for 'a'
> types, the 2nd value is the actual attribute identifier (ex, form type,
> scanner number, etc...). For 'p' types, it refers to the page number.
> Having Cassandra preserve the order of the page numbers is not a priority for
> me, so I can deal with the page number being sorted in String order in the
> database, I'll deal with numerical sorting that in the app logic (since the
> largest documents we process are only about 100 pages long). The 3rd
> composite value is empty for all 'a' types, and for 'p' types, it refers to a
> page level attribute (page landmark information, image skew angle, location
> on disk, etc...).
>
> As an example:
>
> key1 => a:form=x, a:scanner=1425436, p:1:skew=0.0042142, p:1:file=page1.png,
> p:2:skew=0.0042412, p:2:file=page2.png
> key2 => a:form=q, a:scanner=935625, p:1:skew=0.00032352, p:1:file=other1.png,
> p:2:skew=:0.0002355, p:2:file=other2.png
>
> It's been working well for me when using the Hector client.
>
> Thanks,
>
> Mike
>
> On Thu, Sep 13, 2012 at 12:59 PM, Soumya Acharya <cse.sou...@gmail.com> wrote:
> I just started learning Cassandra any suggestion where to start with ??
>
>
> Thanks
> Soumya
>
> On Thu, Sep 13, 2012 at 10:54 AM, Roshni Rajagopal
> <roshni_rajago...@hotmail.com> wrote:
> I want to learn how we can model a mix of static and dynamic columns in a
> family.
>
> Consider a course_students col family which gives a list of students for a
> course
> with row key- Course Id
> Columns - Name, Teach_Nm, StudID1, StudID2, StudID3
> Values - Maths, Prof. Abc, 20,21,25
> where 20,21,25 are IDs of students.
>
> We have
> fixed columns like Course Name, Teacher Name, and a dynamic number of
>
> columns like 'StudID1', 'StudID2' etc, and my thoughts were that we could
>
> look for 'StudID' and get all the columns with the student Ids in Hector. But
> the
>
> question was how would we determine the number for the column, like to add
>
> StudID3 we need to read the row and identify that 2 students are there,
>
> and this is the third one.
>
>
>
> So we can remove the number in the column name, altogether and keep
>
> columns like Course Name, Teacher Name, Student:20,Student:21, Student:25,
>
> where the second part is the actual student id. However here we run into
>
> the second issue that we cannot have some columns of a composite format
>
> and some of another format, when we use static column families- all
>
> columns would need to be in the format UTF8:integer We may want to treat
>
> it as a composite column key and not use a delimiter- to get sorting,
>
> validate the types of the parts of the key, not have to search for the
>
> delimiter and separate the 2 components manually etc.
>
>
>
> A third option is to put only data in the column name for students like
>
> Course Name, Teacher Name, 20,21,25 - it would be difficult to identify
>
> that columns with name 20, 21, 25 actually stand for student names - a bit
>
> unreadable.
>
>
>
> I hope this is not confusing, and would like to hear your thoughts on
> this.The question is
>
> around when you de-normalize & want to have some static info like name ,
>
> and a dynamic list - whats the best way to model this.
>
>
>
> Regards,
>
> Roshni
>
>
>
>
> --
> Regards and Thanks
> Soumya Kanti Acharya
>
