For a personal project, I needed to parse and execute PostgreSQL-compatible jsonpath expressions.¹ So I’ve spent just about every spare evening and weekend the last several months porting Postgres jsonpath to Go, and it’s finally ready to ship.

Introducing Go SQL/JSON, featuring the path package. This project provides full support for all of the PostgresSQL 17 jsonpath features² in the Go programming language. An example:

package main

import (
	"context"
	"encoding/json"
	"fmt"
	"log"

	"github.com/theory/sqljson/path"
	"github.com/theory/sqljson/path/exec"
)

func main() {
	// Parse some JSON.
	var value any
	err := json.Unmarshal([]byte(`{"a":[1,2,3,4,5]}`), &value)
	if err != nil {
		log.Fatal(err)
	}

	// Parse a path expression and execute it on the JSON.
	p := path.MustParse("$.a[*] ? (@ >= $min && @ <= $max)")
	res, err := p.Query(
		context.Background(),
		value,
		exec.WithVars(exec.Vars{"min": float64(2), "max": float64(4)}),
	)
	if err != nil {
		log.Fatal(err)
	}

	fmt.Printf("%v\n", res)
    // Output: [2 3 4]
}

I think the API is decent, but may implement better patterns as I discover them. Overall I’m quite satisfied with how it turned out, and just how well its implementation and performance compare to the original.

🛝 Playground

But why stop there? One of the nice things about this project is that Go supports compiling applications into WebAssembly (a.k.a. Wasm) via Go WebAssembly. Borrowing from the Goldmark project, I created and published the sqljson/path playground and populated the docs with links for all of its examples.

Now anyone can experiment with SQL/JSON path expressions, and share links to demonstrate patterns and techniques. The Playground is a stateless JavaScript/Wasm web application: data persists only in permalink URLs.³

🛝 Try this example Playground permalink right now!⁴

The Path Ahead

I’ve enjoyed learning how to implement a lexer, a goyacc parser, an AST, and an execution engine. The Playground was a bonus bit of fun!

I’m stoked to build cool stuff on this package, but don’t know whether anyone else will find it useful. If you do — or just enjoy messing about on the Playground, let me know!