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How to unnest arrays in JSON documents

In this recipe we'll learn how to unnest or explode values when ingesting JSON documents into Apache Pinot. When we unnest an array it means that we'll create one row in Pinot for each item in the array rather than one row for the whole JSON document.

Pinot Version	0.10.0
Code	startreedata/pinot-recipes/json-unnest

Prerequisites

To follow the code examples in this guide, you must install Docker (opens in a new tab) locally and download recipes.

Navigate to recipe

If you haven't already, download recipes.
In terminal, go to the recipe by running the following command:

cd pinot-recipes/recipes/json-unnest

Launch Pinot Cluster

You can spin up a Pinot Cluster by running the following command:

docker-compose up

This command will run a single instance of the Pinot Controller, Pinot Server, Pinot Broker, and Zookeeper. You can find the docker-compose.yml (opens in a new tab) file on GitHub.

Dataset

We're going to import the following JSON file:

{"Title":"The Matrix","Year":"1999","Rated":"R","Released":"31 Mar 1999","Runtime":"136 min","Genre":"Action, Sci-Fi","Director":"Lana Wachowski, Lilly Wachowski","Writer":"Lilly Wachowski, Lana Wachowski","Actors":"Keanu Reeves, Laurence Fishburne, Carrie-Anne Moss","Plot":"When a beautiful stranger leads computer hacker Neo to a forbidding underworld, he discovers the shocking truth--the life he knows is the elaborate deception of an evil cyber-intelligence.","Language":"English","Country":"United States, Australia","Awards":"Won 4 Oscars. 42 wins & 51 nominations total","Ratings":[{"Source":"Internet Movie Database","Value":"8.7/10"},{"Source":"Rotten Tomatoes","Value":"88%"},{"Source":"Metacritic","Value":"73/100"}],"Metascore":"73","imdbRating":"8.7","imdbVotes":"1,851,767","imdbID":"tt0133093","Type":"movie","DVD":"15 May 2007","BoxOffice":"$172,076,928","Production":"N/A","Website":"N/A","Response":"True"}
{"Title":"Avatar","Year":"2009","Rated":"PG-13","Released":"18 Dec 2009","Runtime":"162 min","Genre":"Action, Adventure, Fantasy","Director":"James Cameron","Writer":"James Cameron","Actors":"Sam Worthington, Zoe Saldana, Sigourney Weaver","Plot":"A paraplegic Marine dispatched to the moon Pandora on a unique mission becomes torn between following his orders and protecting the world he feels is his home.","Language":"English, Spanish","Country":"United States","Awards":"Won 3 Oscars. 89 wins & 131 nominations total","Ratings":[{"Source":"Internet Movie Database","Value":"7.8/10"},{"Source":"Rotten Tomatoes","Value":"82%"},{"Source":"Metacritic","Value":"83/100"}],"Metascore":"83","imdbRating":"7.8","imdbVotes":"1,189,326","imdbID":"tt0499549","Type":"movie","DVD":"22 Apr 2010","BoxOffice":"$760,507,625","Production":"N/A","Website":"N/A","Response":"True"}
{"Title":"The Boss Baby","Year":"2017","Rated":"PG","Released":"31 Mar 2017","Runtime":"97 min","Genre":"Animation, Adventure, Comedy","Director":"Tom McGrath","Writer":"Michael McCullers, Marla Frazee","Actors":"Alec Baldwin, Steve Buscemi, Jimmy Kimmel","Plot":"A suit-wearing, briefcase-carrying baby pairs up with his 7-year old brother to stop the dastardly plot of the CEO of Puppy Co.","Language":"English, Spanish","Country":"United States","Awards":"Nominated for 1 Oscar. 4 wins & 21 nominations total","Ratings":[{"Source":"Internet Movie Database","Value":"6.3/10"},{"Source":"Rotten Tomatoes","Value":"53%"},{"Source":"Metacritic","Value":"50/100"}],"Metascore":"50","imdbRating":"6.3","imdbVotes":"122,684","imdbID":"tt3874544","Type":"movie","DVD":"25 Jul 2017","BoxOffice":"$175,003,033","Production":"N/A","Website":"N/A","Response":"True"}
{"Title":"Tall Girl","Year":"2019","Rated":"TV-PG","Released":"13 Sep 2019","Runtime":"101 min","Genre":"Comedy, Drama, Family","Director":"Nzingha Stewart","Writer":"Sam Wolfson","Actors":"Ava Michelle, Griffin Gluck, Sabrina Carpenter","Plot":"Jodi, the tallest girl in her high school, has always felt uncomfortable in her own skin. But after years of slouching, being made fun of, and avoiding attention at all costs, Jodi finally decides to find the confidence to stand t...","Language":"English","Country":"United States","Awards":"2 wins & 1 nomination","Ratings":[{"Source":"Internet Movie Database","Value":"5.2/10"},{"Source":"Rotten Tomatoes","Value":"38%"}],"Metascore":"N/A","imdbRating":"5.2","imdbVotes":"22,990","imdbID":"tt9252508","Type":"movie","DVD":"13 Sep 2019","BoxOffice":"N/A","Production":"N/A","Website":"N/A","Response":"True"}
{"Title":"Love Hard","Year":"2021","Rated":"TV-MA","Released":"05 Nov 2021","Runtime":"104 min","Genre":"Comedy, Romance","Director":"Hernan Jimenez","Writer":"Daniel Mackey, Rebecca Ewing","Actors":"Nina Dobrev, Jimmy O. Yang, Darren Barnet","Plot":"An LA girl, unlucky in love, falls for an East Coast guy on a dating app and decides to surprise him for the holidays, only to discover that she's been catfished. This lighthearted romantic comedy chronicles her attempt to reel in lo","Language":"English","Country":"United States","Awards":"1 win & 1 nomination","Ratings":[{"Source":"Internet Movie Database","Value":"6.3/10"},{"Source":"Rotten Tomatoes","Value":"57%"},{"Source":"Metacritic","Value":"42/100"}],"Metascore":"42","imdbRating":"6.3","imdbVotes":"48,458","imdbID":"tt10752004","Type":"movie","DVD":"05 Nov 2021","BoxOffice":"N/A","Production":"N/A","Website":"N/A","Response":"True"}

data/movies.json

We're particularly interested in the Ratings property of each movie. We're going to unnest or explode the ratings so that we have one row per rating in our database after the data is ingested.

Pinot Schema and Table

Now let's create a Pinot Schema and Table.

First, the schema:

{
  "schemaName": "movie_ratings",
  "dimensionFieldSpecs": [
    {
      "name": "Title",
      "dataType": "STRING"
    },
    {
      "name": "Year",
      "dataType": "INT"
    },
    {
      "name": "Ratings.Source",
      "dataType": "STRING"
    },
    {
      "name": "Ratings.Value",
      "dataType": "STRING"
    },
    {
      "name": "Rated",
      "dataType": "STRING"
    }
  ]
}

config/schema.json

When we unnest a JSON list in a document, column names will be prefixed with the parent property name, in this case Ratings.

We'll also have the following table config:

{
  "tableName": "movie_ratings",
  "tableType": "OFFLINE",
  "segmentsConfig": {
    "replication": 1,
    "schemaName": "movie_ratings"
  },
  "ingestionConfig": {
    "complexTypeConfig": {
      "fieldsToUnnest": [
        "Ratings"
      ]
    },
    "batchIngestionConfig": {
      "segmentIngestionType": "APPEND",
      "segmentIngestionFrequency": "DAILY"
    },    
  },
  "tenants": {
    "broker": "DefaultTenant",
    "server": "DefaultTenant"
  },
  "tableIndexConfig": {
    "loadMode": "MMAP"
  },
  "metadata": {}
}

config/table.json

The highlighted config specifies which field in the data source should be unnested. The Ratings field contains an array of JSON objects and that array will be exploded to create one row for each item in the array.

💡

If you want to rename the unnested fields, see How to rename fields when unnesting arrays in JSON documents

You can create the table and schema by running the following command:`

docker run \
   --network json \
   -v $PWD/config:/config \
   apachepinot/pinot:1.0.0 AddTable \
     -schemaFile /config/schema.json \
     -tableConfigFile /config/table.json \
     -controllerHost "pinot-controller-json" \
    -exec

You should see a message similar to the following if everything is working correctly:

2022/05/04 09:11:35.397 INFO [AddTableCommand] [main] Executing command: AddTable -tableConfigFile /config/table.json -schemaFile null -controllerProtocol http -controllerHost 192.168.96.3 -controllerPort 9000 -user null -password [hidden] -exec
2022/05/04 09:11:35.614 INFO [AddTableCommand] [main] {"status":"Table movie_ratings_OFFLINE succesfully added"}

Ingestion Job

Now we’re going to import the JSON file into Pinot. We'll do this with the following ingestion spec:

executionFrameworkSpec:
  name: 'standalone'
  segmentGenerationJobRunnerClassName: 'org.apache.pinot.plugin.ingestion.batch.standalone.SegmentGenerationJobRunner'
  segmentTarPushJobRunnerClassName: 'org.apache.pinot.plugin.ingestion.batch.standalone.SegmentTarPushJobRunner'
jobType: SegmentCreationAndTarPush
inputDirURI: '/data'
includeFileNamePattern: 'glob:**/movies.json'
outputDirURI: '/opt/pinot/data/movies/'
overwriteOutput: true
pinotFSSpecs:
  - scheme: file
    className: org.apache.pinot.spi.filesystem.LocalPinotFS
recordReaderSpec:
  dataFormat: 'json'
  className: 'org.apache.pinot.plugin.inputformat.json.JSONRecordReader'
tableSpec:
  tableName: 'movie_ratings'
pinotClusterSpecs:
  - controllerURI: 'http://localhost:9000'
pushJobSpec:
  pushAttempts: 2
  pushRetryIntervalMillis: 1000

config/job-spec.yml

The import job will map fields in each JSON document to a corresponding column in the movie_ratings schema. If one of the fields doesn't exist in the schema it will be skipped.

You can run the following command to run the import:

docker run \
   --network json \
   -v $PWD/config:/config \
   -v $PWD/data:/data \
   apachepinot/pinot:0.12.0-arm64  LaunchDataIngestionJob \
  -jobSpecFile /config/job-spec.yml

Querying

Once that's completed, navigate to localhost:9000/#/query (opens in a new tab) and click on the movie_ratings table or copy/paste the following query:

select * 
from movie_ratings 
limit 10

You will see the following output:

Rated	Ratings.Source	Ratings.Value	Title Year
R	Internet Movie Database	8.7/10	The Matrix
R	Rotten Tomatoes	88%	The Matrix
R	Metacritic	73/100	The Matrix
PG-13	Internet Movie Database	7.8/10	Avatar
PG-13	Rotten Tomatoes	82%	Avatar
PG-13	Metacritic	83/100	Avatar
PG	Internet Movie Database	6.3/10	The Boss Baby
PG	Rotten Tomatoes	53%	The Boss Baby
PG	Metacritic	50/100	The Boss Baby
TV-PG	Internet Movie Database	5.2/10	Tall Girl
TV-PG	Rotten Tomatoes	38%	Tall Girl
TV-MA	Internet Movie Database	6.3/10	Love Hard
TV-MA	Rotten Tomatoes	57%	Love Hard
TV-MA	Metacritic	42/100	Love Hard

Query Results

We can see that each movie has multiple rows, one for each rating given to that movie.

Ingest from Apache Pulsar Rename fields in unnested or flattened JSON documents