Full Documentation
Introduction
An opinionated JSON to CSV/XLSX/SQLITE/PARQUET converter which tries to make a useful relational output for data analysis.
Web playgroud of CSV/XLSX conversions
Rationale
When receiving a JSON file where the structure is deeply nested or not well specified, it is hard to determine what the data contains. Also, even after knowing the JSON structure, it requires a lot of time to work out how to flatten the JSON into a relational structure to do data analysis on and to be part of a data pipeline.
Flatterer aims to be the first tool to go to when faced with the above problem. It may not be the tool that you end up using to flatten the JSON in your data pipeline, as hand written flattening may be required, but it could be. It has many benefits over most hand written approaches:
- It is fast, written in rust but with python bindings for ease of use. It can be 10x faster than hand written python flattening.
- Memory efficient. Uses a custom streaming JSON parser to mean that long list of objects nested with the JSON will be streamed, so not much data needs to be loaded into memory at once.
- Fast memory efficient output to CSV/XLSX/SQLITE/PARQUET
- Uses best practice that has been learnt from flattening JSON countless times, such as generating keys to link one-to-many tables to their parents.
Install
pip install flatterer
Flatterer requires Python 3.6 or greater. It is written as a python extension in Rust but has binaries (wheels) for linux (x64), macos (x64 and universal) and windows (x64, x86). On other platforms a rust toolchain will need to be installed.
Example JSON
Say you have a JSON data like this named games.json
:
[
{
"id": 1,
"title": "A Game",
"releaseDate": "2015-01-01",
"platforms": [
{"name":"Xbox"},
{"name":"Playstation"}
],
"rating": {
"code": "E",
"name": "Everyone"
}
},
{
"id": 2,
"title": "B Game",
"releaseDate": "2016-01-01",
"platforms": [
{"name":"PC"}
],
"rating": {
"code": "E",
"name": "Everyone"
}
}
]
Running Flatterer
Run the above file with flatterer.
flatterer games.json games_dir
Output Files
By running the above you will get the following files:
tree games_dir
games_dir/
├── csv
│ ├── games.csv
│ └── platforms.csv
├── datapackage.json
├── fields.csv
└── ...
Main Table
games.csv
contains:
_link | _link_games | id | rating_code | rating_name | releaseDate | title |
---|
1 | 1 | 1 | E | Everyone | 2015-01-01 | A Game |
2 | 2 | 2 | E | Everyone | 2016-01-01 | B Game |
Special column _link
is generated. _link
is the primary key there unique per game.
Also the rating
sub-object is promoted to this table it has a one-to-one relationship with games
.
Sub-object properties are separated by '_'.
One To Many Table
platforms
is an array so is a one-to-many with games therefore needs its own table:
platforms.csv
contains:
_link | _link_games | name |
---|
1.platforms.0 | 1 | Xbox |
1.platforms.1 | 1 | Playstation |
2.platforms.0 | 2 | PC |
Link Fields
_link
is the primary key for the platforms
table too. Every table except games
table, contains a _link_games
field to easily join to the main games
table.
If there was a sub-array of platforms
then that would have _link
, _link_games
and _link_platforms
fields.
To generalize this the _link__<table_name>
fields joins to the _link
field of <table_name>
i.e the _link__<table_name>
are the foreign keys refrencing <table_name>._link
.
Fields CSV
fields.csv
contains some metadata about the output tables:
table_name | field_name | field_type | count | field_title |
---|
platforms | _link | text | 3 | _link |
platforms | _link_games | text | 3 | _link_games |
platforms | name | text | 3 | name |
games | _link | text | 2 | _link |
games | id | number | 2 | id |
games | rating_code | text | 2 | rating_code |
games | rating_name | text | 2 | rating_name |
games | releaseDate | date | 2 | releaseDate |
games | title | text | 2 | title |
The field_type
column contains a type guess useful for inserting into a database. The field_title
is the column heading in the CSV file or XLSX tab, which is initally the same as the field_name.
After editing this file then you can rerun the transform:
flatterer games.json new_games_dir -f myfields.csv --only-fields
This can be useful for renameing columns, rearranging the field order or if you want to remove some fields the --only-fields
flag will only include the fields in the edited file.
datapackage.json
contains metadata in the Tabular Datapackge Spec