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From "ASF GitHub Bot (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (FLINK-8203) Make schema definition of DataStream/DataSet to Table conversion more flexible
Date Thu, 04 Jan 2018 23:26:00 GMT

    [ https://issues.apache.org/jira/browse/FLINK-8203?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16312184#comment-16312184
] 

ASF GitHub Bot commented on FLINK-8203:
---------------------------------------

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

    https://github.com/apache/flink/pull/5132#discussion_r159757312
  
    --- Diff: flink-libraries/flink-table/src/main/scala/org/apache/flink/table/api/TableEnvironment.scala
---
    @@ -768,6 +768,39 @@ abstract class TableEnvironment(val config: TableConfig) {
         frameworkConfig
       }
     
    +  /**
    +    * Reference input fields by name:
    +    * All fields in the schema definition are referenced by name
    +    * (and possibly renamed using an alias (as). In this mode, fields can be reordered
and
    +    * projected out. Moreover, we can define proctime and rowtime attributes at arbitrary
    +    * positions using arbitrary names (except those that exist in the result schema).
This mode
    +    * can be used for any input type, including POJOs.
    +    *
    +    * Reference input fields by position:
    +    * Field references must refer to existing fields in the input type (except for
    +    * renaming with alias (as)). In this mode, fields are simply renamed. Event-time
attributes can
    +    * replace the field on their position in the input data (if it is of correct type)
or be
    +    * appended at the end. Proctime attributes must be appended at the end. This mode
can only be
    +    * used if the input type has a defined field order (tuple, case class, Row) and no
of fields
    +    * references a field of the input type.
    +    */
    +  protected def isReferenceByPosition(t: TypeInformation[_], fields: Array[Expression]):
Boolean = {
    +    if (t.isInstanceOf[PojoTypeInfo[_]]) {
    +      return false
    +    }
    +
    +    val inputNames = t match {
    +      case ct: CompositeType[_] => ct.getFieldNames
    +      case _ => return false // atomic types are references by name
    --- End diff --
    
    If atomic types are referenced by name, what's the name? Atomic types are neither referenced
by position or name. Instead we can reference the field because there is only one field in
the input.
    
    Should we make this method only available for `CompositeType` by changing the type of
`t` to `CompositeType`?
      


> Make schema definition of DataStream/DataSet to Table conversion more flexible
> ------------------------------------------------------------------------------
>
>                 Key: FLINK-8203
>                 URL: https://issues.apache.org/jira/browse/FLINK-8203
>             Project: Flink
>          Issue Type: Bug
>          Components: Table API & SQL
>    Affects Versions: 1.4.0, 1.5.0
>            Reporter: Fabian Hueske
>            Assignee: Timo Walther
>
> When converting or registering a {{DataStream}} or {{DataSet}} as {{Table}}, the schema
of the table can be defined (by default it is extracted from the {{TypeInformation}}.
> The schema needs to be manually specified to select (project) fields, rename fields,
or define time attributes. Right now, there are several limitations how the fields can be
defined that also depend on the type of the {{DataStream}} / {{DataSet}}. Types with explicit
field ordering (e.g., tuples, case classes, Row) require schema definition based on the position
of fields. Pojo types which have no fixed order of fields, require to refer to fields by name.
Moreover, there are several restrictions on how time attributes can be defined, e.g., event
time attribute must replace an existing field or be appended and proctime attributes must
be appended.
> I think we can make the schema definition more flexible and provide two modes:
> 1. Reference input fields by name: All fields in the schema definition are referenced
by name (and possibly renamed using an alias ({{as}}). In this mode, fields can be reordered
and projected out. Moreover, we can define proctime and eventtime attributes at arbitrary
positions using arbitrary names (except those that existing the result schema). This mode
can be used for any input type, including POJOs. This mode is used if all field references
exist in the input type.
> 2. Reference input fields by position: Field references might not refer to existing fields
in the input type. In this mode, fields are simply renamed. Event-time attributes can replace
the field on their position in the input data (if it is of correct type) or be appended at
the end. Proctime attributes must be appended at the end. This mode can only be used if the
input type has a defined field order (tuple, case class, Row).
> We need to add more tests the check for all combinations of input types and schema definition
modes.



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