[jira] [Commented] (FLINK-5571) add open and close methods for UserDefinedFunction in TableAPI & SQL

["ASF GitHub Bot (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/FLINK-5571?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15853649#comment-15853649 ] 

ASF GitHub Bot commented on FLINK-5571:
---------------------------------------

Github user godfreyhe commented on a diff in the pull request:

    https://github.com/apache/flink/pull/3176#discussion_r99532146
  
    --- Diff: flink-libraries/flink-table/src/main/scala/org/apache/flink/table/codegen/CodeGenerator.scala ---
    @@ -220,56 +247,105 @@ class CodeGenerator(
         // manual casting here
         val samHeader =
           // FlatMapFunction
    -      if (clazz == classOf[FlatMapFunction[_,_]]) {
    +      if (clazz == classOf[FlatMapFunction[_, _]]) {
    --- End diff --
    
    We can not choose `FlatMapFunction` or `RichFlatMapFunction` in `translateToPlan` method, unless We know whether the current rexNode contains `UserDefinedFunction`s. However CodeGenerator is a kind of RexVisitor and know `UserDefinedFunction` when `generateExpression` called. 
    Besides, `RichFlatMapFunction` implements `FlatMapFunction`, so It's reasonable that Users call the generateFunction(desc, classOf[FlatMapFunction[Any, Any]], body, returnType) and returned a RichFlatMapFunction.


> add open and close methods for UserDefinedFunction in TableAPI & SQL
> --------------------------------------------------------------------
>
>                 Key: FLINK-5571
>                 URL: https://issues.apache.org/jira/browse/FLINK-5571
>             Project: Flink
>          Issue Type: New Feature
>          Components: Table API & SQL
>            Reporter: godfrey he
>            Assignee: godfrey he
>
> Currently, a User Defined Function (UDF) in table API & SQL works on zero, one, or multiple values in custom evaluation method. Many UDFs need more complex features, e.g. report metrics, get parameters from job configuration, or get extra data from distribute cache file, etc. Adding open and close methods in UserDefinedFunction class can solve this problem. The code cloud look like:
> {code}
> trait UserDefinedFunction {
>   def open(context: UDFContext): Unit = {}
>   def close(): Unit = {}
> }
> {code}
> UDFContext contains the information about metric reporters, job parameters, distribute cache, etc. The code cloud look like:
> {code}
> class UDFContext(context: RuntimeContext) {
>   def getMetricGroup: MetricGroup = ???
>   def getDistributedCacheFile(name: String): File = ???
>   def getJobParameter(key: String, default: String): String = ???
> }
> {code}



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