8.9. Avro Converter¶

The Avro converter handles data written by Apache Avro. To use the Avro converter, specify type = "avro" in your converter definition.

8.9.1. Configuration¶

The Avro converter supports parsing whole Avro files, with the schema embedded, or Avro IPC messages with the schema omitted. For an embedded schema, set schema = "embedded" in your converter definition. For IPC messages, specify the schema in one of two ways: to use an inline schema string, set schema = "<schema string>"; to use a schema defined in a separate file, set schema-file = "<path to file>".

The Avro record being parsed is available to field transforms as $1.

8.9.2. Avro Paths¶

Avro paths are defined similarly to JSONPath or XPath, and allow you to extract specific fields out of an Avro record. An Avro path consists of forward-slash delimited strings. Each part of the path defines a field name with an optional predicate:

$type=<typename> - match the Avro schema type name on the selected element
[$<field>=<value>] - match elements with a field named “field” and a value equal to “value”

For example, /foo$type=bar/baz[$qux=quux]. See Example Usage, below, for a concrete example.

Avro paths are available through the avroPath transform function, as described below.

8.9.3. Avro Transform Functions¶

GeoMesa defines several Avro-specific transform functions.

8.9.3.1. avroPath¶

Description: Extract values from nested Avro structures.

Usage: avroPath($ref, $pathString)

$ref - a reference object (avro root or extracted object)
pathString - forward-slash delimited path strings. See Avro Paths, above

8.9.3.2. avroBinaryList¶

GeoMesa has a custom Avro schema for writing SimpleFeatures. List, map and UUID attributes are serialized as binary Avro fields. This function can read a serialized list-type attribute.

Description: Parses a binary Avro value as a list

Usage: avroBinaryList($ref)

8.9.3.3. avroBinaryMap¶

GeoMesa has a custom Avro schema for writing SimpleFeatures. List, map and UUID attributes are serialized as binary Avro fields. This function can read a serialized map-type attribute.

Description: Parses a binary Avro value as a map

Usage: avroBinaryMap($ref)

8.9.3.4. avroBinaryUuid¶

GeoMesa has a custom Avro schema for writing SimpleFeatures. List, map and UUID attributes are serialized as binary Avro fields. This function can read a serialized UUID-type attribute.

Description: Parses a binary Avro value as a UUID

Usage: avroBinaryUuid($ref)

8.9.4. Example Usage¶

For this example we’ll use the following Avro schema in a file named /tmp/schema.avsc:

{
  "namespace": "org.locationtech",
  "type": "record",
  "name": "CompositeMessage",
  "fields": [
    { "name": "content",
      "type": [
         {
           "name": "DataObj",
           "type": "record",
           "fields": [
             {
               "name": "kvmap",
               "type": {
                  "type": "array",
                  "items": {
                    "name": "kvpair",
                    "type": "record",
                    "fields": [
                      { "name": "k", "type": "string" },
                      { "name": "v", "type": ["string", "double", "int", "null"] }
                    ]
                  }
               }
             }
           ]
         },
         {
            "name": "OtherObject",
            "type": "record",
            "fields": [{ "name": "id", "type": "int"}]
         }
      ]
   }
  ]
}

This schema defines an avro file that has a field named content which has a nested object which is either of type DataObj or OtherObject. As an exercise, we can use avro tools to generate some test data and view it:

java -jar /tmp/avro-tools-1.7.7.jar random --schema-file /tmp/schema -count 5 /tmp/avro

$ java -jar /tmp/avro-tools-1.7.7.jar tojson /tmp/avro
{"content":{"org.locationtech.DataObj":{"kvmap":[{"k":"thhxhumkykubls","v":{"double":0.8793488185997134}},{"k":"mlungpiegrlof","v":{"double":0.45718223406586045}},{"k":"mtslijkjdt","v":null}]}}}
{"content":{"org.locationtech.OtherObject":{"id":-86025408}}}
{"content":{"org.locationtech.DataObj":{"kvmap":[]}}}
{"content":{"org.locationtech.DataObj":{"kvmap":[{"k":"aeqfvfhokutpovl","v":{"string":"kykfkitoqk"}},{"k":"omoeoo","v":{"string":"f"}}]}}}
{"content":{"org.locationtech.DataObj":{"kvmap":[{"k":"jdfpnxtleoh","v":{"double":0.7748286862915655}},{"k":"bueqwtmesmeesthinscnreqamlwdxprseejpkrrljfhdkijosnogusomvmjkvbljrfjafhrbytrfayxhptfpcropkfjcgs","v":{"int":-1787843080}},{"k":"nmopnvrcjyar","v":null},{"k":"i","v":{"string":"hcslpunas"}}]}}}

Here’s a more relevant sample record:

{
  "content" : {
    "org.locationtech.DataObj" : {
      "kvmap" : [ {
        "k" : "lat",
        "v" : {
          "double" : 45.0
        }
      }, {
        "k" : "lon",
        "v" : {
          "double" : 45.0
        }
      }, {
        "k" : "prop3",
        "v" : {
          "string" : " foo "
        }
      }, {
        "k" : "prop4",
        "v" : {
          "double" : 1.0
        }
      } ]
    }
  }
}

Let’s say we want to convert our Avro array of kvpairs into a simple feature. We notice that there are 4 attributes:

lat
lon
prop3
prop4

The following converter config would be sufficient to parse the Avro:

{
  type        = "avro"
  schema-file = "/tmp/schema.avsc"
  sft         = "testsft"
  id-field    = "uuid()"
  fields = [
    { name = "tobj", transform = "avroPath($1, '/content$type=DataObj')" },
    { name = "lat",  transform = "avroPath($tobj, '/kvmap[$k=lat]/v')" },
    { name = "lon",  transform = "avroPath($tobj, '/kvmap[$k=lon]/v')" },
    { name = "geom", transform = "point($lon, $lat)" }
  ]
}