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From Roshni Rajagopal <Roshni.Rajago...@wal-mart.com>
Subject Re: Setting column to null
Date Tue, 12 Jun 2012 05:20:00 GMT
Leonid,


Are you using some client for doing these operations..?

Hector is a java client which provides APIs for adding/deleting columns to
a column family in cassandra.
I don¹t think you really need to write your wrapper in this format- you
are restricting the number of columns it can use etc.I suggest your code
can  accept user input to get col family name, operation, keys  , and
operation, and accordingly call the appropriate hector API for
adding/deleting data.


Regards,
Roshni


On 11/06/12 7:20 PM, "Leonid Ilyevsky" <lilyevsky@mooncapital.com> wrote:

>Thanks, I understand what you are telling me. Obviously deleting the
>column is the proper way to do this in Cassandra.
>What I was looking for, is some convenient wrapper on top of that which
>will do it for me. Here is my scenario.
>
>I have a function that takes a record to be saved in Cassandra (array of
>objects, or Map<String, Object>). Let say, it can have up to 8 columns. I
>prepare a statement like this:
>
>Insert into <table> values(?, ?, ?, ?, ?, ?, ?, ?)
>
>If I somehow could put null when I execute it, it would be enough to
>prepare that statement once and execute it multiple times. I would then
>expect that when some element is null, the corresponding column is not
>inserted (for the new key) or deleted (for the existing key).
>The way it is now, in my code I have to examine which columns are present
>and which are not, depending on that I have to generate customized
>statement, and it is going to be different for the case of existing key
>versus case of the new key.
>Isn't this too much hassle?
>
>Related question. I assumed that prepared statement in Cassandra is there
>for the same reason as in RDBMS, that is, for efficiency. In the above
>scenario, how expensive is it to execute specialized statement for every
>record compare to prepared statement executed multiple times?
>
>If I need to execute those specialized statements, should I still use
>prepared statement or should I just generate a string with everything in
>ascii format?
>
>-----Original Message-----
>From: Roshni Rajagopal [mailto:Roshni.Rajagopal@wal-mart.com]
>Sent: Monday, June 11, 2012 12:58 AM
>To: user@cassandra.apache.org
>Subject: Re: Setting column to null
>
>Would you want to view data like this "there was a key, which had this
>column , but now it does not have any value as of this time."
>
>Unless you specifically want this information, I believe you should just
>delete the column, rather than have an alternate value for NULL or create
>a composite column.
>
>Because in cassandra that¹s the way deletion is dealt with, putting NULLs
>is the way we deal with it in RDBMS because we have a fixed number of
>columns which always have to have some value, even if its NULL, and we
>have to have the same set of columns for every row.
>In Cassandara, we can delete the column, and in most scenarios that¹s
>what we should do, unless we specifically want to preserve some history
>that this column was turned null at this timeŠEach row can have different
>columns.
>
>Regards,
>Roshni
>
>From: Edward Capriolo
><edlinuxguru@gmail.com<mailto:edlinuxguru@gmail.com>>
>Reply-To: "user@cassandra.apache.org<mailto:user@cassandra.apache.org>"
><user@cassandra.apache.org<mailto:user@cassandra.apache.org>>
>To: "user@cassandra.apache.org<mailto:user@cassandra.apache.org>"
><user@cassandra.apache.org<mailto:user@cassandra.apache.org>>
>Subject: Re: Setting column to null
>
>Your best bet is to define the column as a composite column where one
>part represents is null and the other part is the data.
>
>On Friday, June 8, 2012, shashwat shriparv
><dwivedishashwat@gmail.com<mailto:dwivedishashwat@gmail.com>> wrote:
>> What you can do is you can define some specific variable like
>>"NULLDATA" some thing like that to update in columns that does have value
>>
>>
>> On Fri, Jun 8, 2012 at 11:58 PM, aaron morton
>><aaron@thelastpickle.com<mailto:aaron@thelastpickle.com>> wrote:
>>
>> You don't nee to set columns to null, delete the column instead.
>> Cheers
>> -----------------
>> Aaron Morton
>> Freelance Developer
>> @aaronmorton
>> http://www.thelastpickle.com
>> On 8/06/2012, at 9:34 AM, Leonid Ilyevsky wrote:
>>
>> Is it possible to explicitly set a column value to null?
>>
>> I see that if insert statement does not include a specific column, that
>>column comes up as null (assuming we are creating a record with new
>>unique key).
>> But if we want to update a record, how we set it to null?
>>
>> Another situation is when I use prepared cql3 statement (in Java) and
>>send parameters when I execute it. If I want to leave some column
>>unassigned, I need a special statement without that column.
>> What I would like is, prepare one statement including all columns, and
>>then be able to set some of them to null. I tried to set corresponding
>>ByteBuffer parameter to null, obviously got an exception.
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>> --
>>
>>
>> ƒ
>>
>> Shashwat Shriparv
>>
>>
>
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