sqlite-template-inja

SQLite extension for templating with Inja

sqlite> select template_render('my first choice fruit is {{fruit.0}} but I also like {{fruit.1}}', JSON_OBJECT("fruit", JSON_ARRAY("banana", "apple", "mango")));

my first choice fruit is banana but I also like apple

Very rough initial revision with crude error-checking and exception-handling.

Developed on WSL but should run on anything with a modern C++ compiler due to the excellent portability of sqlite, inja and nlohmann::json.

Building

I followed the instructions in https://visitlab.pages.fi.muni.cz/tutorials/vs-code/index.html to use CMake and vcpkg.

For each remote machine (in my case wsl2 and Mac), I hand-edited the user-settings for the remote machine e.g. /Users/phrrngtn/.vscode-server/data/Machine/settings.json with this seemingly redundant setting but I was not able to get it to work using only one.

{
    "cmake.configureArgs": [
        "-DCMAKE_TOOLCHAIN_FILE=/Users/phrrngtn/work/vcpkg/scripts/buildsystems/vcpkg.cmake"
    ],
    "cmake.configureSettings": {
        "CMAKE_TOOLCHAIN_FILE": "/Users/phrrngtn/work/vcpkg/scripts/buildsystems/vcpkg.cmake"
    },
}

Here is how to do it by hand if you don't want to use VS code

cmake .. -DCMAKE_TOOLCHAIN_FILE=/home/phrrngtn/work/vcpkg/scripts/buildsystems/vcpkg.cmake -DVCPKG_TARGET_TRIPLET=x64-linux

• load

-- On Windows, Linux and Mac.
sqlite> .load ./inja

sqlite> select * FROM pragma_function_list where name = 'template_render';
template_render|0|s|utf8|3|2048

• extension exports just one function, template_render which takes an Inja template string and a JSON object (and, optionally, a JSON object for configuration) and returns the template rendered wrt the JSON data.

select template_render('what is a  {{fruit}}, if not perfection', json_object('fruit', 'banana'));

what is a  banana, if not perfection

There is an optional third argument which if present will be interpreted as a JSON object with keys of comment, expression, statement and line_statement and used to construct an inja::Environment pointer with options set as per https://github.com/pantor/inja#template-rendering

For example, to use C-style comments in the template source, you would pass an object like this:

JSON_OBJECT('comment', json_array('/*', '*/'))

or a JSON literal:

'{"comment" : ["/*", "*/"]}'

This mechanism from Inja was exposed to support templating of ODBC connection strings where curly braces ('{}') are used extensively and clash with the Inja default expression delimiters of {{ and }}.

Error handling is still a bit rough

-- bogus JSON (passed in a string that looks like JSON but isn't)
sqlite> select template_render('what is a  {{}}, if not perfection', '{"fruitdsf", "banana"}');

Runtime error: [json.exception.parse_error.101] parse error at line 1, column 12: syntax error while parsing object separator - unexpected ','; expected ':'

-- fix the JSON (as a string literal) but with an invalid template
sqlite> select template_render('what is a  {{}}, if not perfection', '{"fruitdsf": "banana"}');

Runtime error: Inja exception: empty expression(render_error)

-- valid template structure but wrong key in the JSON
sqlite> select template_render('what is a  {{fruit}}, if not perfection', JSON_OBJECT("fruitdsf", "banana"));

Runtime error: Inja exception: variable 'fruit' not found(render_error)