sqlite-diffable by simonw

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README

sqlite-diffable

PyPI Changelog License

Tools for dumping/loading a SQLite database to diffable directory structure

Installation

pip install sqlite-diffable

Demo

The repository at simonw/simonwillisonblog-backup contains a backup of the database on my blog, https://simonwillison.net/ - created using this tool.

Dumping a database

Given a SQLite database called fixtures.db containing a table facetable, the following will dump out that table to the dump/ directory:

sqlite-diffable dump fixtures.db dump/ facetable

To dump out every table in that database, use --all:

sqlite-diffable dump fixtures.db dump/ --all

Loading a database

To load a previously dumped database, run the following:

sqlite-diffable load restored.db dump/

This will show an error if any of the tables that are being restored already exist in the database file.

You can replace those tables (dropping them before restoring them) using the --replace option:

sqlite-diffable load restored.db dump/ --replace

Converting to JSON objects

Table rows are stored in the .ndjson files as newline-delimited JSON arrays, like this:

["a", "a", "a-a", 63, null, 0.7364712141640124, "$null"]
["a", "b", "a-b", 51, null, 0.6020187290499803, "$null"]

Sometimes it can be more convenient to work with a list of JSON objects.

The sqlite-diffable objects command can read a .ndjson file and its accompanying .metadata.json file and output JSON objects to standard output:

sqlite-diffable objects fixtures.db dump/sortable.ndjson

The output of that command looks something like this:

{"pk1": "a", "pk2": "a", "content": "a-a", "sortable": 63, "sortable_with_nulls": null, "sortable_with_nulls_2": 0.7364712141640124, "text": "$null"}
{"pk1": "a", "pk2": "b", "content": "a-b", "sortable": 51, "sortable_with_nulls": null, "sortable_with_nulls_2": 0.6020187290499803, "text": "$null"}

Add -o to write that output to a file:

sqlite-diffable objects fixtures.db dump/sortable.ndjson -o output.txt

Add --array to output a JSON array of objects, as opposed to a newline-delimited file:

sqlite-diffable objects fixtures.db dump/sortable.ndjson --array

Output:

[
{"pk1": "a", "pk2": "a", "content": "a-a", "sortable": 63, "sortable_with_nulls": null, "sortable_with_nulls_2": 0.7364712141640124, "text": "$null"},
{"pk1": "a", "pk2": "b", "content": "a-b", "sortable": 51, "sortable_with_nulls": null, "sortable_with_nulls_2": 0.6020187290499803, "text": "$null"}
]

Storage format

Each table is represented as two files. The first, table_name.metadata.json, contains metadata describing the structure of the table. For a table called redirects_redirect that file might look like this:

{
    "name": "redirects_redirect",
    "columns": [
        "id",
        "domain",
        "path",
        "target",
        "created"
    ],
    "schema": "CREATE TABLE [redirects_redirect] (\n   [id] INTEGER PRIMARY KEY,\n   [domain] TEXT,\n   [path] TEXT,\n   [target] TEXT,\n   [created] TEXT\n)"
}

It is an object with three keys: name is the name of the table, columns is an array of column strings and schema is the SQL schema text used for tha table.

The second file, table_name.ndjson, contains newline-delimited JSON for every row in the table. Each row is represented as a JSON array with items corresponding to each of the columns defined in the metadata.

That file for the redirects_redirect.ndjson table might look like this:

[1, "feeds.simonwillison.net", "swn-everything", "https://simonwillison.net/atom/everything/", "2017-10-01T21:11:36.440537+00:00"]
[2, "feeds.simonwillison.net", "swn-entries", "https://simonwillison.net/atom/entries/", "2017-10-01T21:12:32.478849+00:00"]
[3, "feeds.simonwillison.net", "swn-links", "https://simonwillison.net/atom/links/", "2017-10-01T21:12:54.820729+00:00"]