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From Sylvain Lebresne <sylv...@datastax.com>
Subject Re: is this correct, thrift unportable to CQL3Š.
Date Wed, 25 Sep 2013 07:22:25 GMT
On Tue, Sep 24, 2013 at 7:24 PM, Hiller, Dean <Dean.Hiller@nrel.gov> wrote:

> Java has Integer as opposed to int which is what I represent "golf scores"
> with so to speak in my example.  In this case, Integer can be null but of
> course maps to "empty" just fine.  What about querying for all golf scores
> that are "empty" then?
>

The DataStax java driver already "maps" a null Integer to a null CQL3
column, and so it *cannot* also map it to an empty value. And even though
you cannot have null CQL3 columns in the primary key, mapping a null
Integer to an empty value would be highly confusing/inconsistent (from the
point of view of the java driver) because:
1) having a null Integer map differently depending on whether the receiving
column is in the PK or not would be messy/surprising.
2) it's not really technically possible because internally the driver does
not always have the information of whether the receiving column is in the
PK or not
3) what about strings? Should we also map a null String to an empty value
when the column is in the PK? Because that would mean mapping a null java
String to an empty CQL3 string value and that just feel wrong. And if we
don't do it, then it means we treat Integer and String differently with
respect to null and that's too would be pretty confusing.

But anyway, all of that is pretty specific to the java driver, so maybe if
you guys want to debate that further we should move to the driver mailing
list:
https://groups.google.com/a/lists.datastax.com/forum/#!forum/java-driver-user

--
Sylvain


>
> Ie. This sounds like this solution would be perfect if we can get rid of
> the exception piece.
>
> Thanks much!!!
> Dean
>
> From: Sylvain Lebresne <sylvain@datastax.com<mailto:sylvain@datastax.com>>
> Reply-To: "user@cassandra.apache.org<mailto:user@cassandra.apache.org>" <
> user@cassandra.apache.org<mailto:user@cassandra.apache.org>>
> Date: Tuesday, September 24, 2013 10:58 AM
> To: "user@cassandra.apache.org<mailto:user@cassandra.apache.org>" <
> user@cassandra.apache.org<mailto:user@cassandra.apache.org>>
> Subject: Re: is this correct, thrift unportable to CQL3Š.
>
> On Tue, Sep 24, 2013 at 6:17 PM, Vikas Goyal <vikas@easility.com<mailto:
> vikas@easility.com>> wrote:
> Ok. Great. It works for String and Decimal/Float but not for integer data
> type..
> i.e,, if I am passing "" to the composite key column which is either text
> or float, it works..
>
> session.execute(boundStatement.bind(rowkey, "", ByteBuffer.wrap(value)));
>
> But not working with bigint, int or varint..and getting following
> exception;
>
> Exception:Invalid type for value 1 of CQL type varint, expecting class
> java.math.BigInteger but class java.lang.String provided
>
> ..I am exploring more though..
>
> We're getting into details of the java driver at this point. For int, what
> you can do is:
>   boundStatement.setString("id", rowkey);
>   boundStatement.setBytesUnsafe("columnname", ByteBuffer.wrap(new
> byte[0]));
>   boundStatement.setBytes("columnvalue", ByteBuffer.wrap(value));
>
> In other words, the shorthand BoundStatement.bind() won't let you insert
> an empty value for types
> that don't naturally have an empty value (like int; keep in mind that an
> empty value is not the same
> than null). But you can circumvent that using setBytesUnsafe if you really
> want.
>
> Long story short, my advice would be to avoid using empty values for type
> that don't naturally have
> one (anything else than text and blob really). If you do, that's going to
> be painful (but possible) to
> work with, at least with the java driver (but for good reasons, java just
> doesn't have a good to
> represent an empty int value (again, you can have a null Integer but
> that's different)).
>
> --
> Sylvain
>
>
> Thanks a ton,
> Vikas Goyal
>
>
> On Tue, Sep 24, 2013 at 9:05 PM, Sylvain Lebresne <sylvain@datastax.com
> <mailto:sylvain@datastax.com>> wrote:
>
> However,we tried missing the value but it didn't work :(
>
> Right, because not providing a value is akin to having a null value (in
> the CQL3 sense of the term, which is different from what Dean asked about)
> and null values are not allowed for primary key columns.
> You could however insert an *empty* value if you wanted, which in you case
> is just inserting an empty string since colname is a string. Thrift doesn't
> allow more or less in that case.
>
> --
> Sylvain
>
>
>
> So our code is like below where we are using 3 values if colname is not
> null..else 2 values..
>
>             if (key != null) {
>                 PreparedStatement statement = session.prepare("INSERT INTO
> keys.StringIndice (id, colname, colvalue) VALUES (?, ?, ?)");
>                 BoundStatement boundStatement = new
> BoundStatement(statement);
>
> session.execute(boundStatement.bind(StandardConverters.convertFromBytes(String.class,
> rowKey), key, ByteBuffer.wrap(value)));
>             } else {
>                 PreparedStatement statement = session.prepare("INSERT INTO
> " + keys + "." + table + "(id, colvalue) VALUES (?, ?)");
>                 BoundStatement boundStatement = new
> BoundStatement(statement);
>
> session.execute(boundStatement.bind(StandardConverters.convertFromBytes(String.class,
> rowKey), ByteBuffer.wrap(value)));
>           }
>
> And, I did that and getting this exception:
>
> Exception:Missing PRIMARY KEY part colname since colvalue is set
>
> And just FYI. Our Column Family definition is below:
>
> CREATE TABLE keys.StringIndice (id text,
> colname text,
> colvalue blob,
> PRIMARY KEY (id,colname, colvalue)) WITH COMPACT STORAGE)
>
> Thanks again,
> Vikas Goyal
>
>
>
> On Tue, Sep 24, 2013 at 7:02 PM, Sylvain Lebresne <sylvain@datastax.com
> <mailto:sylvain@datastax.com>> wrote:
> Short answer: not, this is not correct.
>
> Longer answer: what you call "null" is actually an empty value (which is
> *not* the same thing, unless you consider an empty string is the same thing
> than a null string). As it happens, C* always an empty value as a valid
> value for any type and that's true of both thrift and CQL3. What is true is
> that CQL3 discourage the use of empty values for type for which it doesn't
> particularly make sense (integers typically) by not having a particular
> easy to use syntax to input them. But that's supported nonetheless. If you
> use a prepared statement for instance (where you send values already
> serialized), nothing will prevent you from sending an empty value. Even if
> you don't want to use a prepared statement, CQL3 has conversion functions (
> http://cassandra.apache.org/doc/cql3/CQL.html#blobFun) that allows to do
> it (for instance, "blobAsInt(0x)" will be an empty int value).
>
> --
> Sylvain
>
>
>
> On Tue, Sep 24, 2013 at 2:36 PM, Hiller, Dean <Dean.Hiller@nrel.gov
> <mailto:Dean.Hiller@nrel.gov>> wrote:
> Many applications in thrift use the wide row with composite column name
> and as an example, let's say golf score for instance and we end up with
> golf score : pk like so
>
> null : pk56
> null : pk45
> 89 : pk90
> 89: pk87
> 90: pk101
> 95: pk17
>
> Notice that there are some who do not have a golf score(zero would not
> quite make sense and would be interpreted as a golf score).  I am hearing
> from this post if they are correct that this is not portable to CQL3???  Is
> this true?
> http://stackoverflow.com/questions/18963248/how-can-i-have-null-column-value-for-a-composite-key-column-in-cql3
>
> (This sounds like a major deficit to me as the wide row now can only be
> used where actual values exist?????).  Is it possible to port this pattern
> to CQL3?
>
> Thanks,
> Dean
>
>
>
>
>
>
>
>

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