How can i check if a list is exsisting in a redis database using node-redis?-CodePudding

I am trying to create a custom list according to the route accessed from the root route. I am using express routing parameters to get the name of the list and add some predefined values to the list.

But i want to check first if the specified name (list name) hasn't already been used by another list in the Redis database. I am using the client.exists command to check if the specified key(list name) exists but it doesn't seem to work at all. Here is my code:

app.get("/:customListName", (req, res) => {
  const customListName = req.params.customListName;
  console.log(customListName);

  client.exists(customListName, (err, reply) => {
    if (reply === 0) {
      console.log("Doesn't exist!");

      const multi = client.multi();
      const customList = ["Have fun!", "Play Games!", "Watch Movies!"];
      customList.forEach((item) => {
        multi.rPush(customListName, item);
      });
      multi.exec();
    } else {
      console.log("Exists!");
    }
  });
});

From the code i have logged the accessed route and a message that specifies if a list exists or else but am surprised to see that the route is shown (which is 'home' in this case) but no message is logged as you can see below:

[nodemon] 2.0.20
[nodemon] to restart at any time, enter `rs`
[nodemon] watching path(s): *.*
[nodemon] watching extensions: js,mjs,json
[nodemon] starting `node app.js`
home

CodePudding user response：

Node Redis 4.x uses Promises instead of callbacks. My guess is you are using that version and that this is the source of your problem. Try this:

app.get("/:customListName", async (req, res) => {
  const customListName = req.params.customListName;
  const itExists = await client.exists(customListName);
  if (itExists) {
    /* do one thing */
  } else {
    /* do something else */
  }
});

Not 100% sure but I think the .exists command returns a boolean. But regardless, it'll certainly be truthy or falsy and so this code will work either way.