[jira] [Commented] (AVRO-1340) use default to allow old readers to specify default enum value when encountering new enum symbols

[Zoltan Farkas (JIRA)]

    [ 
https://issues.apache.org/jira/browse/AVRO-1340?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16137220#comment-16137220
 ] 

Zoltan Farkas commented on AVRO-1340:
-------------------------------------

[~cutting] what do you thing about the following:

 1) Symbol aliases example to correct misspellings. (similar to field 
aliasses):  

v1:

{code}
{ "type": "enum",
  "name": "Suit",
  "symbols" : ["SPADES", "HEARTS", "DIAMONDS", "CLUS"]
}
{code}

v2:

{code}
{ "type": "enum",
  "name": "Suit",
  "symbols" : ["SPADES", "HEARTS", "DIAMONDS", "CLUB”]
  “symbolAliasses” : {
      “CLUB” : [“CLUS”]
  }
}
{code}

v3:

{code}
{ "type": "enum",
  "name": "Suit",
  "symbols" : ["SPADES", "HEARTS", "DIAMONDS", "CLUBS”]
  “symbolAliasses” : {
      “CLUBS” : [“CLUS”, “CLUB”]
  }
}
{code}

sample conversion:

v1: { “val” : “CLUS”} <-> v3: { “val” : “CLUBS” }

the following enum schema would be illegal:

{code}
{ "type": "enum",
  "name": "Suit",
  "symbols" : ["SPADES", "HEARTS", "DIAMONDS", "CLUBS”]
  “symbolAliasses” : {
      “CLUBS” : [“CLUS”, “CLUB”, “SPADES”]
  }
}
{code}

since it contains a duplicate definition. (“SPADES”, “CLUBS”)


 2) Evolution example with a fallback symbol:

V1:

{code}
{ "type": "enum",
  "name": "Suit",
  "symbols" : [“UNKNOWN”, ”SPADES", "HEARTS", "DIAMONDS", "CLUBS”],
  “symbolAliasses” : {
      “CLUBS” : [“CLUS”, “CLUB”]
  },
  “fallbackSymbol” : “UNKNOWN”
}
{code}

and a record using the above enum:

{code}
{
  "type": "record",
  "name": “Example”,
  "fields" : [
    {"name": “enumValue”,
      "type": “Suit”,
      “default” : “SPADES”},
  ]
}
{code}

V2:

{code}
{ "type": "enum",
  "name": "Suit",
  "symbols" : [“UNKNOWN”, ”SPADES", "HEARTS", "DIAMONDS", "CLUBS”, “NEWVAL”]
  “symbolAliasses” : {
      “CLUBS” : [“CLUS”, “CLUB”],
  },
  “fallbackSymbol” : “UNKNOWN”
}
{code}

sample conversion:

v2 : { “enumValue” : “NEWVAL” } -> v1 : {“enumValue” : “UNKNOWN”}
v1: {“enumValue” : “UNKNOWN”} -> v2  : {“enumValue” : “UNKNOWN”}

would this be acceptable?




> use default to allow old readers to specify default enum value when 
> encountering new enum symbols
> -------------------------------------------------------------------------------------------------
>
>                 Key: AVRO-1340
>                 URL: https://issues.apache.org/jira/browse/AVRO-1340
>             Project: Avro
>          Issue Type: Improvement
>          Components: spec
>         Environment: N/A
>            Reporter: Jim Donofrio
>            Priority: Minor
>
> The schema resolution page says:
> > if both are enums:
> > if the writer's symbol is not present in the reader's enum, then an
> error is signalled.
> This makes it difficult to use enum's because you can never add a enum value 
> and keep old reader's compatible. Why not use the default option to refer to 
> one of enum values so that when a old reader encounters a enum ordinal it 
> does not recognize, it can default to the optional schema provided one. If 
> the old schema does not provide a default then the older reader can continue 
> to fail as it does today.



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