Ruby Avro: Record schema reports datum is not valid

Question

I am trying to serialize a JSON using avro and a schema. This is not a rails app (despite the tag, I needed the attention), so I could also use map however, neither of the following work.

schema = { 'type' => 'record', 'name' => 'test', 'fields' => [ { 'name' => 'field_one', 'type' => 'string' },
                                                               { 'name' => 'field_two', 'type' => 'string'},
                                                               { 'name' => 'field_three', 'type' => 'string'},
                                                               { 'name' => 'field_four', 'type' => 'string' } ] }.to_json
message = {'field_one' => 'why',
             'field_two' => 'this',
             'field_three' => 'no',
             'field_four' => 'worky?'}.to_json
schema = Avro::Schema.parse(schema)
dw = Avro::IO::DatumWriter.new(schema)
buffer = StringIO.new()
encoder = Avro::IO::BinaryEncoder.new(buffer)
dw.write(message, encoder)
puts buffer.read

returns: 'The datum ... is not an example of schema ...'

Replacing schema from above with the following:

schema = { 'type' => 'map', 'values' => 'string' }.to_json

results in: 'undefined method `keys' for StringObject'

Not sure, why I can't create a simple map with string:string key:values. The ruby documentation for for Avro is awful; very few actual example and a lot of placeholder templates which leave a lot to the imagination. I'd like to be able to put this serialized string object into an http request with type application/json, which may be an issue since avro wants to be binary.

Answer 1

require 'avro'
require 'json'

schema = { 'type' => 'record', 'name' => 'Test', 'fields' => [ { 'name' => 'field_one', 'type' => 'string' },
                                                               { 'name' => 'field_two', 'type' => 'string'},
                                                               { 'name' => 'field_three', 'type' => 'string'},
                                                               { 'name' => 'field_four', 'type' => 'string' } ] }.to_json

message = {'field_one' => 'why',
             'field_two' => 'this',
             'field_three' => 'no',
             'field_four' => 'worky?'}

schema = Avro::Schema.parse(schema)
writer = Avro::IO::DatumWriter.new(schema)
buffer = StringIO.new
writer = Avro::DataFile::Writer.new(buffer, writer, schema)
writer << message
writer.close # important

result = buffer.string

puts result