UDF/User Defined Functions in Cassandra 3.x

I was just playing around with Cassandra WRITETIME and thought it was somewhat difficult to figure out the date / timestamp of a number like this (microseconds since EPOC) 1470645914253000.

So in my example it looked like this

cqlsh:bth> select id, writetime(dateofbirth) from bth.employee;

 id | writetime(dateofbirth)
----+------------------------
  1 |       1470645914253000
  2 |       1470645977177000
  7 |       1470948508799001
  3 |       1470645977178000

(4 rows)
cqlsh:bth>

cqlsh:bth> select id, writetime(dateofbirth) from bth.employee;

id | writetime(dateofbirth)

----+------------------------

1 | 1470645914253000

2 | 1470645977177000

7 | 1470948508799001

3 | 1470645977178000

(4 rows)

cqlsh:bth>

So I figured why not create a UDF that would solve this for me

That turned out to be a little bit of a challenge …

I thought that I could do like this

CREATE FUNCTION bth.ts2date ( input bigint )
	RETURNS NULL ON NULL INPUT
    RETURNS text 
    LANGUAGE java
    AS $$
    	if( input > 0L ) {
    		long ms = input / 1000L;
    		Date date=new Date(ms);
    		SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss,SSS");
    		return sdf.format(date);
    	} else return null;
    $$;

CREATE FUNCTION bth.ts2date ( input bigint )

RETURNS NULL ON NULL INPUT

RETURNS text

LANGUAGE java

AS $$

if( input > 0L ) {

long ms = input / 1000L;

Date date=new Date(ms);

SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss,SSS");

return sdf.format(date);

} else return null;

$$;

BUT NO, YOU CAN NOT!!!

There are several WRONGS in here it turns out

First off you have to turn on
enable_user_defined_functions: true
in the conf/cassandra.yaml file
All classes has to be fully qualified, so Date would be java.util.Date, and so on…
The division operator ‘/’ can not be used !!! however +,- and * works fine. surely this must be a bug … this called for some thinking…

The error I got when trying to use the code above without fully qualified names was

cqlsh> CREATE FUNCTION ts2date ( input bigint )
   ... RETURNS NULL ON NULL INPUT
   ...     RETURNS text 
   ...     LANGUAGE java
   ...     AS $$
   ...     if( input != null ) {
   ...     Date date=new Date(mills);
InvalidRequest: code=2200 [Invalid query] message="Functions must be fully qualified with a keyspace name if a keyspace is not set for the session"

cqlsh> CREATE FUNCTION ts2date ( input bigint )

... RETURNS NULL ON NULL INPUT

... RETURNS text

... LANGUAGE java

... AS $$

... if( input != null ) {

... Date date=new Date(mills);

InvalidRequest: code=2200 [Invalid query] message="Functions must be fully qualified with a keyspace name if a keyspace is not set for the session"

And the reason, if I got it right, is that you can not do imports.

The error I got when trying to use the division ‘/’ operator was this:

cqlsh:bth> CREATE FUNCTION bth.ts2date ( input bigint )
       ... RETURNS NULL ON NULL INPUT
       ...     RETURNS text 
       ...     LANGUAGE java
       ...     AS $$
       ...     if( input > 0L ) {
       ...     java.util.Date date=new java.util.Date(input/1000);
Invalid syntax at line 7, char 49
      java.util.Date date=new java.util.Date(input/1000);
                                                  ^
cqlsh:bth>

cqlsh:bth> CREATE FUNCTION bth.ts2date ( input bigint )

... RETURNS NULL ON NULL INPUT

... RETURNS text

... LANGUAGE java

... AS $$

... if( input > 0L ) {

... java.util.Date date=new java.util.Date(input/1000);

Invalid syntax at line 7, char 49

java.util.Date date=new java.util.Date(input/1000);

cqlsh:bth>

The code that works looks like this, using java.math.BigDecimal to solve it was perhaps a so-so solution, but it works:

CREATE FUNCTION bth.ts2date ( input bigint ) 
RETURNS NULL ON NULL INPUT     
RETURNS text      
LANGUAGE java     
AS $$     
	if( input > 0L ) {     
		java.math.BigDecimal t = java.math.BigDecimal.valueOf(1000L);     
		java.math.BigDecimal inp = java.math.BigDecimal.valueOf(input);     
		java.math.BigDecimal mst = inp.divide(t); 
		long ms = mst.longValue();     
		java.util.Date date=new java.util.Date(ms);     
		java.text.SimpleDateFormat sdf = new java.text.SimpleDateFormat("yyyy-MM-dd HH:mm:ss,SSS");     
		return sdf.format(date);     
	} else return null;     
$$;

CREATE FUNCTION bth.ts2date ( input bigint )

RETURNS NULL ON NULL INPUT

RETURNS text

LANGUAGE java

AS $$

if( input > 0L ) {

java.math.BigDecimal t = java.math.BigDecimal.valueOf(1000L);

java.math.BigDecimal inp = java.math.BigDecimal.valueOf(input);

java.math.BigDecimal mst = inp.divide(t);

long ms = mst.longValue();

java.util.Date date=new java.util.Date(ms);

java.text.SimpleDateFormat sdf = new java.text.SimpleDateFormat("yyyy-MM-dd HH:mm:ss,SSS");

return sdf.format(date);

} else return null;

$$;

So now my output in cqlsh.sh looks like this now

cqlsh:bth> select id, ts2date(writetime(dateofbirth)) from bth.employee;

 id | bth.ts2date(writetime(dateofbirth))
----+-------------------------------------
  1 |             2016-08-08 10:45:14,253
  2 |             2016-08-08 10:46:17,177
  7 |             2016-08-11 22:48:28,799
  3 |             2016-08-08 10:46:17,178

(4 rows)
cqlsh:bth>

cqlsh:bth> select id, ts2date(writetime(dateofbirth)) from bth.employee;

id | bth.ts2date(writetime(dateofbirth))

----+-------------------------------------

1 | 2016-08-08 10:45:14,253

2 | 2016-08-08 10:46:17,177

7 | 2016-08-11 22:48:28,799

3 | 2016-08-08 10:46:17,178

(4 rows)

cqlsh:bth>

That is a lot better !

tsoft.se

Tobias – With a Passion For Software Development

UDF/User Defined Functions in Cassandra 3.x

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