Fwd: AvroStorage/Avro Schema Question

[Russell Jurney <ru...@gmail.com>]

I am having trouble with ARRAY_ELEM getting injected into my pig data, when
I store.  Scott Carey had good insight into how to address the issue.

---------- Forwarded message ----------
From: Scott Carey <sc...@apache.org>
Date: Mon, Apr 2, 2012 at 9:13 AM
Subject: Re: AvroStorage/Avro Schema Question
To: user@avro.apache.org


It appears as though the Avro to PigStorage schema translation names (in
pig) all arrays ARRAY_ELEM.  The nullable wrapper is 'visible' and the
field name is not moved onto the bag name.

About a year and a half ago I started
https://issues.apache.org/jira/browse/AVRO-592

but before finishing it AvroStorage was written elsewhere.  I don't recall
exactly what I did with the schema translation there, but I recall the
mapping from an Avro schema to pig tried to hide the nullable wrappers more.


In Avro, arrays are unnamed types, so I see two things you could probably
do without any code changes:

* Add a line in the pig script to project / rename the fields to what you
want (unfortunate and clumbsy, but I think it will work — I think you want
"from::PIG_WRAPPER::ARRAY_ELEM as from"  or
"FLATTEN(from::PIG_WRAPPER)::ARRAY_ELEM as from" something like that.
* Add a record wrapper to your schema (which may inject more messiness in
the pig schema view):
{
    "namespace": "agile.data.avro",
    "name": "Email",
    "type": "record",
    "fields": [
        {"name":"message_id", "type": ["string", "null"]},
        {"name":"from","type": [{"type":"record", "name":"From", "fields":
[[{"type":"array", "items":"string"},"null"]], "null"]},
       …
    ]
}

But that is very awkward — requiring a named record for each field that is
an unnamed type.


Ideally PigStorage would treat any union of null and one other thing as a
simple pig type with no wrapper, and project the name of a field or record
into the name of the thing inside a bag.


-Scott

On 3/29/12 6:05 PM, "Russell Jurney" <ru...@gmail.com> wrote:

Is it possible to name string elements in the schema of an array?
 Specifically, below I want to name the email addresses in the
from/to/cc/bcc/reply_to fields, so they don't get auto-named ARRAY_ELEM by
Pig's AvroStorage.  I know I can probably fix this in Java in the Pig
AvroStorage UDF, but I'm hoping I can also fix it more easily in the
schema.  Last time I read Avro's array docs in this context, my hit-points
dropped by a third, so pardom me if I've not rtfm this time :)

Complete description of what I'm doing follows:

Avro schema for my emails:

{
    "namespace": "agile.data.avro",
    "name": "Email",
    "type": "record",
    "fields": [
        {"name":"message_id", "type": ["string", "null"]},
        {"name":"from","type": [{"type":"array", "items":"string"},
"null"]},
        {"name":"to","type": [{"type":"array", "items":"string"}, "null"]},
        {"name":"cc","type": [{"type":"array", "items":"string"}, "null"]},
        {"name":"bcc","type": [{"type":"array", "items":"string"}, "null"]},
        {"name":"reply_to", "type": [{"type":"array", "items":"string"},
"null"]},
        {"name":"in_reply_to", "type": [{"type":"array", "items":"string"},
"null"]},
        {"name":"subject", "type": ["string", "null"]},
        {"name":"body", "type": ["string", "null"]},
        {"name":"date", "type": ["string", "null"]}
    ]
}


Pig to publish my Avros:

grunt> emails = load '/me/tmp/emails' using AvroStorage();
grunt> describe emails

emails: {message_id: chararray,from: {PIG_WRAPPER: (ARRAY_ELEM:
chararray)},to: {PIG_WRAPPER: (ARRAY_ELEM: chararray)},cc: {PIG_WRAPPER:
(ARRAY_ELEM: chararray)},bcc: {PIG_WRAPPER: (ARRAY_ELEM:
chararray)},reply_to: {PIG_WRAPPER: (ARRAY_ELEM: chararray)},in_reply_to:
{PIG_WRAPPER: (ARRAY_ELEM: chararray)},subject: chararray,body:
chararray,date: chararray}

grunt> store emails into 'mongodb://localhost/agile_data.emails' using
MongoStorage();


My emails in MongoDB:

> db.emails.findOne()
{
"_id" : ObjectId("4f738a35414e113e75707b97"),
"message_id" : "<4f...@li169-134.mail>",
"from" : [
{
"ARRAY_ELEM" : "daily@jobchangealerts.com"
}
],
"to" : [
{
"ARRAY_ELEM" : "Russell.jurney@gmail.com"
}
],
"cc" : null,
"bcc" : null,
"reply_to" : null,
"in_reply_to" : null,
"subject" : "Daily Job Change Alerts from SalesLoft",
"body" : "Daily Job Change Alerts from SalesLoft",
"date" : "2012-03-27T08:00:29"
}


My email on screen:

[image: Inline image 1]

My face when I see ARRAY_ELEM, because it means more complex presentation
code: *:(*
-- 
Russell Jurney twitter.com/rjurney russell.jurney@gmail.com datasyndrome.com




-- 
Russell Jurney twitter.com/rjurney russell.jurney@gmail.com datasyndrome.com