Tool to generate a Hive schema from a JSON example doc
Java
Latest commit 23b5014 Sep 20, 2015 @quux00 Updated README
Corrected typos in the classpath as outlined in Issue #6

README.md

Overview

The best tool for using JSON docs with Hive is rcongui's openx Hive-JSON-Serde. When using that JSON Serde, you define your Hive schema based on the contents of the JSON.

Hive schemas understand arrays, maps and structs. You can map a JSON array to a Hive array and a JSON "object" to either a Hive map or struct. I prefer to map JSON objects to structs.

This tool will take a curated JSON document and generate the Hive schema (CREATE TABLE statement) for use with the openx Hive-JSON-Serde. I say "curated" because you should ensure that every possible key is present (with some arbitrary value of the right data type) and that all arrays have at least one entry.

If the curated JSON example you provide has more than one entry in an array, only the first one will be examined, so you should ensure that it has all the fields.

For more information on using the openx Hive-JSON-SerDe, see my blog post entry.

Build

mvn package

Creates json-hive-schema-1.0.jar and json-hive-schema-1.0-jar-with-dependencies.jar in the target directory.

Usage

with the non-executable jar

java -cp target/json-hive-schema-1.0.jar net.thornydev.JsonHiveSchema file.json

# optionally specify the name of the table
java -cp target/json-hive-schema-1.0.jar net.thornydev.JsonHiveSchema file.json my_table_name

with the executable jar

java -jar target/json-hive-schema-1.0-jar-with-dependencies.jar file.json

java -jar target/json-hive-schema-1.0-jar-with-dependencies.jar file.json my_table_name

Both print the Hive schema to stdout.

Example:

Suppose I have the JSON document:

{
  "description": "my doc",
  "foo": {
    "bar": "baz",
    "quux": "revlos",
    "level1" : {
      "l2string": "l2val",
      "l2struct": {
        "level3": "l3val"
      }
    }
  },
  "wibble": "123",
  "wobble": [
    {
      "entry": 1,
      "EntryDetails": {
        "details1": "lazybones",
        "details2": 414
      }
    },
    {
      "entry": 2,
      "EntryDetails": {
        "details1": "entry 123"
      }
    }
  ]
}

I recommend distilling it down to a doc with a single entry in each array and one that has all possible keys filled in - the values don't matter as long as they are present and a type can be determined.

So for the curated version of the JSON I've removed one of the entries from the "wobble" array and ensured that the remaining one has all the fields:

{
  "description": "my doc",
  "foo": {
    "bar": "baz",
    "quux": "revlos",
    "level1" : {
      "l2string": "l2val",
      "l2struct": {
        "level3": "l3val"
      }
    }
  },
  "wibble": "123",
  "wobble": [
    {
      "entry": 1,
      "EntryDetails": {
        "details1": "lazybones",
        "details2": 414
      }
    }
  ]
}

Now generate the schema:

$ java -jar target/json-hive-schema-1.0-jar-with-dependencies.jar in.json TopQuark
CREATE TABLE TopQuark (
  description string,
  foo struct<bar:string, level1:struct<l2string:string, l2struct:struct<level3:string>>, quux:string>,
  wibble string,
  wobble array<struct<entry:int, entrydetails:struct<details1:string, details2:int>>>)
ROW FORMAT SERDE 'org.openx.data.jsonserde.JsonSerDe';

You can then load your data into Hive and run queries like this:

hive > select wobble.entry, wobble.EntryDetails.details1, wobble.EntryDetails[0].details2 from TopQuark;
entry   details1                    details2
[1,2]   ["lazybones","entry 123"]   414
Time taken: 15.665 seconds