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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.

note

Pre-requisites

You will need to install Docker locally to follow the code examples in this guide.

Download Recipe

First, clone the GitHub repository to your local machine and navigate to this recipe:

git clone git@github.com:startreedata/pinot-recipes.git
cd pinot-recipes/recipes/json-unnest

If you don't have a Git client, you can also download a zip file that contains the code and then navigate to the recipe.

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 file on GitHub.

Dataset

We're going to import the following JSON file:

data/movies.json
{"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"}

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:

config/schema.json
{
"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"
}
]
}

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

You can create the schema by running the following command:

docker exec -it pinot-controller-json bin/pinot-admin.sh AddSchema \
-schemaFile /config/schema.json \
-exec

We'll also have the following table config:

config/table.json
{
"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": {}
}

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.

tip

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

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

docker exec -it pinot-controller-json bin/pinot-admin.sh AddTable \
-tableConfigFile /config/table.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:

config/job-spec.yml
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'

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 exec -it pinot-controller-json bin/pinot-admin.sh LaunchDataIngestionJob \
-jobSpecFile /config/job-spec.yml

Querying

Once that's completed, navigate to localhost:9000/#/query 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:

RatedRatings.SourceRatings.ValueTitle Year
RInternet Movie Database8.7/10The Matrix
RRotten Tomatoes88%The Matrix
RMetacritic73/100The Matrix
PG-13Internet Movie Database7.8/10Avatar
PG-13Rotten Tomatoes82%Avatar
PG-13Metacritic83/100Avatar
PGInternet Movie Database6.3/10The Boss Baby
PGRotten Tomatoes53%The Boss Baby
PGMetacritic50/100The Boss Baby
TV-PGInternet Movie Database5.2/10Tall Girl
TV-PGRotten Tomatoes38%Tall Girl
TV-MAInternet Movie Database6.3/10Love Hard
TV-MARotten Tomatoes57%Love Hard
TV-MAMetacritic42/100Love Hard

Query Results

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