SQLite tables can contain binary data in ``BLOB`` columns.
Datasette includes special handling for these binary values. The Datasette interface detects binary values and provides a link to download their content, for example on https://latest.datasette.io/fixtures/binary_data
Binary data is represented in ``.json`` exports using Base64 encoding. Datasette uses this representation for every ``BLOB`` value, including binary values that could also be decoded as UTF-8 text.
The same format can be used with the :ref:`JSON write API <json_api_write>`.
If a column value in a ``row``, ``rows`` or ``update`` object is a JSON object with exactly ``"$base64"`` set to ``true`` and an ``"encoded"`` string, Datasette will decode that Base64 string and store the resulting bytes:
..code-block:: json
{
"data": {
"$base64": true,
"encoded": "FRwCx60F/g=="
}
}
This works for inserts, upserts and updates. It also works when creating a table from example ``row`` or ``rows`` data: Datasette decodes the value before inferring the schema, allowing that column to be created as a ``BLOB`` column.
To store a JSON object with that exact shape literally, wrap it in a ``"$raw"`` object:
..code-block:: json
{
"data": {
"$raw": {
"$base64": true,
"encoded": "FRwCx60F/g=="
}
}
}
``"$raw"`` unwraps exactly one layer. To store a literal ``"$raw"`` object containing a Base64 object, wrap it again:
The ``.blob`` output format is used to return binary data. It requires a ``_blob_column=`` query string argument specifying which BLOB column should be downloaded, for example:
This output format can also be used to return binary data from an arbitrary SQL query. Since such queries do not specify an exact row, an additional ``?_blob_hash=`` parameter can be used to specify the SHA-256 hash of the value that is being linked to.
Consider the query ``select data from binary_data`` - `demonstrated here <https://latest.datasette.io/fixtures?sql=select+data+from+binary_data>`__.
That page links to the binary value downloads. Those links look like this:
These ``.blob`` links are also returned in the ``.csv`` exports Datasette provides for binary tables and queries, since the CSV format does not have a mechanism for representing binary data.
Binary plugins
--------------
Several Datasette plugins are available that change the way Datasette treats binary data.
-`datasette-render-binary <https://github.com/simonw/datasette-render-binary>`__ modifies Datasette's default interface to show an automatic guess at what type of binary data is being stored, along with a visual representation of the binary value that displays ASCII strings directly in the interface.
-`datasette-render-images <https://github.com/simonw/datasette-render-images>`__ detects common image formats and renders them as images directly in the Datasette interface.
-`datasette-media <https://github.com/simonw/datasette-media>`__ allows Datasette interfaces to be configured to serve binary files from configured SQL queries, and includes the ability to resize images directly before serving them.
