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https://issues.apache.org/jira/browse/CASSANDRA-7395?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14041923#comment-14041923
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Robert Stupp commented on CASSANDRA-7395:
-----------------------------------------
bq. Let's not over-think it at first
just have that idea and keep it in mind
I currently have some "spec" for UDF declaration in mind which is not directly
related to {{Function}} interface.
A "UDF class scanner" collects all classes annotated with {{@UDFBundle}} and
all methods annotated with {{@UDF}}.
Methods' return types and parameter types are mapped to CQL types. Ambigious
types (like UUID) can be specialized using an annotation parameter but have a
default mapping (e.g. UUID = timeuuid, String = text).
Primitive Java types would be only allowed as return types. UDF method
parameter types must use the "object" variant to allow {{null}} handling.
Means: (de)serialization is done outside of the UDF implementation if not
explicitly requested.
This shall keep the UDF implementation itself "simple" without the need to
explicitly build (de)serialization code - which may lead to a lot of
copy-and-paste code in UDFs making them unnecessarily big.
{noformat}
@UDFBundle(name = "foobar")
public class MyUDFs {
@UDF(
name = "sin",
deterministic = true // flag which can be used later for "function
based indexes"
)
public Double sinForDouble(Double input) {
return input == null ? null : Math.sin(input);
}
@UDF(name = "sin", deterministic=true)
public Float sinForFloat(Float input) {
return input == null ? null : Math.sin(input);
}
@UDF(
deterministic = true,
paramTypes = { "timeuuid" }
)
public Date timeuuidToDate(UUID uuid) { ... }
@UDF(
deterministic = true,
paramTypes = { "text" }
)
public Integer some(ByteBuffer blob) // gets "raw" data
@UDF(
deterministic = true,
paramTypes = { "list<timeuuid>" }
)
public List<Date> timeuuidToDate(List<UUID> uuid) { ... }
@UDF(
name = "mysuperhash",
deterministic = true
)
// a UDF that can handle any data type
public Long someSpecialHashFunctionThatTakesAnyDataType(
org.apache.cassandra.udf.TypeAndData anyType ) {
AbstractType type = any.getType();
ByteBuffer value = any.getValue();
}
}
{noformat}
Is this something worth to discuss?
> Support for pure user-defined functions (UDF)
> ---------------------------------------------
>
> Key: CASSANDRA-7395
> URL: https://issues.apache.org/jira/browse/CASSANDRA-7395
> Project: Cassandra
> Issue Type: New Feature
> Components: API, Core
> Reporter: Jonathan Ellis
> Fix For: 3.0
>
> Attachments: 7395.diff
>
>
> We have some tickets for various aspects of UDF (CASSANDRA-4914,
> CASSANDRA-5970, CASSANDRA-4998) but they all suffer from various degrees of
> ocean-boiling.
> Let's start with something simple: allowing pure user-defined functions in
> the SELECT clause of a CQL query. That's it.
> By "pure" I mean, must depend only on the input parameters. No side effects.
> No exposure to C* internals. Column values in, result out.
> http://en.wikipedia.org/wiki/Pure_function
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