How to query from within Mongoose pre hook in a Node.js / Express app?

Question

I'm building a basic blog in Node.js / Express using MongoDB w/ Mongoose ORM.

I have a pre 'save' hook that I'd like to use to auto-generate a blog/idea slug for me. This works fine and well, except for the part where I want to query to see if there are any other existing posts with the same slug before continuing.

However, it appears that this does not have access to .find or .findOne() and so I keep getting an error.

What's the best way to approach this?

  IdeaSchema.pre('save', function(next) {     var idea = this;      function generate_slug(text) {       return text.toLowerCase().replace(/[^\w ]+/g,'').replace(/ +/g,'-').trim();     };      idea.slug = generate_slug(idea.title);      // this has no method 'find'     this.findOne({slug: idea.slug}, function(err, doc) {       console.log(err);       console.log(doc);     });      //console.log(idea);     next();   }); 

Answer 1

Unfortunately, it's not documented very well (no mention of it in the Document.js API docs), but Documents have access to their models through the constructor field - I use it all the time for logging things from plugins, which gives me access to which model they're attached to.

module.exports = function readonly(schema, options) {     schema.pre('save', function(next) {         console.log(this.constructor.modelName + " is running the pre-save hook.");          // some other code here ...          next();     }); }); 

For your situation, you should be able to do:

IdeaSchema.pre('save', function(next) {     var idea = this;      function generate_slug(text) {         return text.toLowerCase().replace(/[^\w ]+/g,'').replace(/ +/g,'-').trim();     };      idea.slug = generate_slug(idea.title);      // this now works     this.constructor.findOne({slug: idea.slug}, function(err, doc) {         console.log(err);         console.log(doc);         next(err, doc);     });      //console.log(idea); }); 

Answer 2

In this you have got the document, not the model. Method findOne is not present on the document.

If you need the model, you can always retrieve it as is shown here. But more clever would be to just assign the model to a variable at the point of creation. Then use this variable anywhere you desire. If it is in another file, then use module.exports and require to get it anywhere else in your project. Something like this:

var mongoose = require('mongoose'); var Schema = mongoose.Schema; mongoose.connect('mongodb://localhost/dbname', function (err) { // if we failed to connect, abort if (err) throw err; var IdeaSchema = Schema({     ... }); var IdeaModel = mongoose.model('Idea', IdeaSchema); IdeaSchema.pre('save', function(next) {     var idea = this;      function generate_slug(text) {         return text.toLowerCase().replace(/[^\w ]+/g,'').replace(/ +/g,'-').trim();     };      idea.slug = generate_slug(idea.title);      // this has no method 'find'     IdeaModel.findOne({slug: idea.slug}, function(err, doc) {         console.log(err);         console.log(doc);     });      //console.log(idea);     next();    }); // we connected ok })