Node.js App with Neo4j

Let's quickly write up a quick Node.js project to help you transfer your skills from the command line to the coding world.

[You can access all samples for this project here][samples].

Make a new directory. In that directory run:

npm init -y
npm i express neo4j-driver@4.1.2 express@4.17.1
mkdir static
touch static/index.html server.js
code . # or open this folder in VS Code or whatever editor you want

Let's make a dumb front end that just makes search queries against the backend. In static/index.html put:

<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>Neo4j Sample</title>
  </head>
  <body>
    <input type="text" placeholder="Person 1" id="person1" />
    <input type="text" placeholder="Person 2" id="person2" />
    <button id="btn">Search</button>
    <pre>
        <code id="code"></code>
    </pre>

    <script>
      const btn = document.getElementById("btn");
      const code = document.getElementById("code");
      const person1 = document.getElementById("person1");
      const person2 = document.getElementById("person2");

      btn.addEventListener("click", async () => {
        code.innerText = "loading";

        const res = await fetch(
          `/get?person1=${encodeURIComponent(
            person1.value
          )}&person2=${encodeURIComponent(person2.value)}`
        );
        const json = await res.json();

        code.innerText = "\n" + JSON.stringify(json, null, 4);
      });
    </script>
  </body>
</html>

Normally I'd say don't put a big script tag in there but we're going for simplicity right now. You can refactor this later to something better.
It'd be way better if we had a dropdown of all actors, actresses, and directors in the graph instead of freeform text. I'll leave you to make that query and update the UI.

In server.js, put this:

const express = require("express");
const neo4j = require("neo4j-driver");

const CONNECTION_STRING =
  process.env.NEO4J_CONNECTION_STRING || "bolt://localhost:7687";

const driver = neo4j.driver(NEO4J_CONNECTION_STRING);

async function init() {
  const app = express();

  app.get("/get", async (req, res) => {
    const session = driver.session();
    const result = await session.run(
      `
        MATCH path = shortestPath(
            (First:Person {name: $person1 })-[*]-(Second:Person {name: $person2 })
        )
        UNWIND nodes(path) as node
        RETURN coalesce(node.name, node.title) as text;
    `,
      {
        person1: req.query.person1,
        person2: req.query.person2,
      }
    );

    res.json({
      status: "ok",
      path: result.records.map((record) => record.get("text")),
    });

    await session.close();
  });

  app.use(express.static("./static"));
  app.listen(process.env.PORT || 3000);
}
init();

Neo4j has its own transfer protocol (as opposed to HTTP) called bolt. Both PostgreSQL and MongoDB have their own too.
Like PostgreSQL's pools, Neo4j's driver does that for you and gives you a client via a session. Make sure you close sessions when you're done so connections can be reused.
We're doing a parameterized query just like PostgreSQL. As you can see you're sending a string to Neo4j which is the interpreting that string as a command. Any time this is happening you could suffer an injection attack. Luckily you can do the same thing here with a parameterized query so the driver ensures nothing bad can be injected.
This is basically the Kevin Bacon query but generalized to be any two people.
Neo4j gives you back a list of Record objects and you have to call get() on each of the records to get the attributes you want which is what we did with the map statement to get each of the names and titles.

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Graph – Node.js App with Neo4j

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Node.js App with Neo4j