bigquery-schema-generator 0.2.0

Summary

This script generates the BigQuery schema from the newline-delimited JSON data records on the STDIN. The BigQuery data importer (bq load) uses only the first 100 lines when the schema auto-detection feature is enabled. In contrast, this script uses all data records to generate the schema.

Usage:

$ generate-schema < file.data.json > file.schema.json

Background

Data can be imported into BigQuery using the bq command line tool. It accepts a number of data formats including CSV or newline-delimited JSON. The data can be loaded into an existing table or a new table can be created during the loading process. The structure of the table is defined by its schema. The table’s schema can be defined manually or the schema can be auto-detected.

When the auto-detect feature is used, the BigQuery data importer examines only the first 100 records of the input data. In many cases, this is sufficient because the data records were dumped from another database and the exact schema of the source table was known. However, for data extracted from a service (e.g. using a REST API) the record fields could have been organically added at later dates. In this case, the first 100 records do not contain fields which are present in later records. The bq load auto-detection fails and the data fails to load.

The bq load tool does not support the ability to process the entire dataset to determine a more accurate schema. This script fills in that gap. It processes the entire dataset given in the STDIN and outputs the BigQuery schema in JSON format on the STDOUT. This schema file can be fed back into the bq load tool to create a table that is more compatible with the data fields in the input dataset.

Installation

Install from PyPI repository using pip3. If you want to install the package for your entire system globally, use

$ sudo -H pip3 install bigquery_schema_generator

If you are using a virtual environment (such as venv), then you don’t need the sudo coommand, and you can just type:

$ pip3 install bigquery_schema_generator

A successful install should print out the following:

Collecting bigquery-schema-generator
Installing collected packages: bigquery-schema-generator
Successfully installed bigquery-schema-generator-0.1.4

The shell script generate-schema is installed in the same directory as pip3.

Usage

The generate_schema.py script accepts a newline-delimited JSON data file on the STDIN. (CSV is not supported currently.) It scans every record in the input data file to deduce the table’s schema. It prints the JSON formatted schema file on the STDOUT. There are at least 3 ways to run this script:

1) Shell script

If you installed using pip3, then it should have installed a small helper script named generate-schema in your local ./bin directory of your current environment (depending on whether you are using a virtual environment).

$ generate-schema < file.data.json > file.schema.json

2) Python module

You can invoke the module directly using:

$ python3 -m bigquery_schema_generator.generate_schema < file.data.json > file.schema.json

This is essentially what the generate-schema command does.

3) Python script

If you retrieved this code from its GitHub repository, then you can invoke the Python script directly:

$ ./generate_schema.py < file.data.json > file.schema.json

$ bq load --source_format NEWLINE_DELIMITED_JSON \
        --schema file.schema.json \
        mydataset.mytable \
        file.data.json

$ bq show --schema mydataset.mytable | python -m json.tool

$ generate-schema --help
usage: generate_schema.py [-h] [--keep_nulls]
                          [--debugging_interval DEBUGGING_INTERVAL]
                          [--debugging_map]

Generate BigQuery schema.

optional arguments:
  -h, --help            show this help message and exit
  --keep_nulls          Print the schema for null values, empty arrays or
                        empty records.
  --debugging_interval DEBUGGING_INTERVAL
                        Number of lines between heartbeat debugging messages.
  --debugging_map       Print the metadata schema_map instead of the schema
                        for debugging

$ generate_schema
{ "s": null, "a": [], "m": {} }
^D
INFO:root:Processed 1 lines
[]

$ generate-schema --keep_nulls
{ "s": null, "a": [], "m": {} }
^D
INFO:root:Processed 1 lines
[
  {
    "mode": "REPEATED",
    "type": "STRING",
    "name": "a"
  },
  {
    "mode": "NULLABLE",
    "fields": [
      {
        "mode": "NULLABLE",
        "type": "STRING",
        "name": "__unknown__"
      }
    ],
    "type": "RECORD",
    "name": "d"
  },
  {
    "mode": "NULLABLE",
    "type": "STRING",
    "name": "s"
  }
]

$ generate-schema --debugging_interval 50 < file.data.json > file.schema.json

$ generate-schema --debugging_map < file.data.json > file.schema.json

Schema Types

Examples

Here is an example of a single JSON data record on the STDIN (the ^D below means typing Control-D, which indicates “end of file” under Linux and MacOS):

$ generate-schema
{ "s": "string", "b": true, "i": 1, "x": 3.1, "t": "2017-05-22T17:10:00-07:00" }
^D
INFO:root:Processed 1 lines
[
  {
    "mode": "NULLABLE",
    "name": "b",
    "type": "BOOLEAN"
  },
  {
    "mode": "NULLABLE",
    "name": "i",
    "type": "INTEGER"
  },
  {
    "mode": "NULLABLE",
    "name": "s",
    "type": "STRING"
  },
  {
    "mode": "NULLABLE",
    "name": "t",
    "type": "TIMESTAMP"
  },
  {
    "mode": "NULLABLE",
    "name": "x",
    "type": "FLOAT"
  }
]

In most cases, the data file will be stored in a file:

$ cat > file.data.json
{ "a": [1, 2] }
{ "i": 3 }
^D

$ generate-schema < file.data.json > file.schema.json
INFO:root:Processed 2 lines

$ cat file.schema.json
[
  {
    "mode": "REPEATED",
    "name": "a",
    "type": "INTEGER"
  },
  {
    "mode": "NULLABLE",
    "name": "i",
    "type": "INTEGER"
  }
]

System Requirements

This project was developed on Ubuntu 17.04 using Python 3.5.3. I have tested it on:

• Ubuntu 17.04, Python 3.5.3

• Ubuntu 16.04, Python 3.5.2

• MacOS 10.13.2, Python 3.6.4

Author

Created by Brian T. Park (brian@xparks.net).

License

Apache License 2.0