• 1. Install & Set up mongoose -

     Add mongodb and mongoose to the project's package.json. Then require mongoose. Store your mLab database URI in the private .env file as MONGO-URI. Connect to the database using mongoose.connect(<Your URI>) const mongoose - require('mongoose'); mongoose.connect(process.env.MONGO-URI, { useNewUrlParser: true });

• 2. Create a 'Person' Model -

     • First of all we need a Schema. Each schema maps to a MongoDB collection and defines the shape of the documents within that collection. Schemas are building block for Models. They can be nested to create complex models, but in this case we'll keep things simple. A model allows you to create instances of your objects, called documents.

     • Create a person having this prototype :

           - Person Prototype -
               name : string [required]
               age : number
               favoriteFoods : array of strings ()
       

     • Use the mongoose basic -schema types-. If you want you can also add more fields, use simple validators like required or unique, and set default values. See the mongoose docs.

     • Note: Glitch is a real server, and in real servers interactions with the db are placed in handler functions, to be called when some event happens (e.g. someone hits an endpoint on your API). We'll follow the same approach in these exercises. The done() function is a callback that tells us that we can proceed after completing an asynchronous operation such as inserting, searching, updating or deleting. It's following the Node convention and should be called as done(null, data) on success, or done(err) on error. Warning - When interacting with remote services, errors may occur !

       ```
       - Example -
       var someFunc - function(done) {
       ... do something (risky) ...
       if(error) return done(error);
       done(null, result);
       };
       ```
       

• 3. Create and Save a Person -

     • Create a document instance using the Person constructor you build before. Pass to the constructor an object having the fields name, age, and favoriteFoods. Their types must be conformant to the ones in the Person Schema. Then call the method document.save() on the returned document instance, passing to it a callback using the Node convention. This is a common pattern, all the CRUD methods take a callback function like this as the last argument.

       - Example -
       ...
       person.save(function(err, data) {
       ...do your stuff here...
       });
       

     • 4. Create many People with Model.create() -

Sometimes you need to create many Instances of your Models, e.g. when seeding a database with initial data. Model.create() takes an array of objects like [{name: 'John', ...}, {...}, ...], as the 1st argument, and saves them all in the db. Create many people using Model.create(), using the function argument 'arrayOfPeople'.

• C[R]UD part II - READ

• 5. Use Model.find() -

Find all the people having a given name, using Model.find() -> [Person] In its simplest usage, Model.find() accepts a query document (a JSON object ) as the first argument, and returns an array of matches. It supports an extremely wide range of search options. Check it in the docs. Use the function argument personName as search key.

• 6. Use Model.findOne() -

Model.findOne() behaves like .find(), but it returns only one document, even if there are more. It is especially useful when searching by properties that you have declared as unique. Find just one person which has a certain food in her favorites, using Model.findOne() -> Person. Use the function argument food as search key

• 7. Use Model.findById() -

When saving a document, mongodb automatically add the field -id, and set it to a unique alphanumeric key. Searching by -id is an extremely frequent operation, so moongose provides a dedicated method for it. Find the (only!!) person having a certain Id, using Model.findById() -> Person. Use the function argument 'personId' as search key.

• CR[U]D part III - UPDATE

• 8. Classic Update : Find, Edit then Save -

In the good old days this was what you needed to do if you wanted to edit a document and be able to use it somehow e.g. sending it back in a server response. Mongoose has a dedicated updating method : Model.update(), which is directly binded to the low-level mongo driver. It can bulk edit many documents matching certain criteria, but it doesn't pass the edited document to its callback, only a 'status' message. Furthermore it makes validation difficult, because it just direcly calls the mongodb driver.

Find a person by Id ( use any of the above methods ) with the parameter personId as search key. Add "hamburger" to the list of her favoriteFoods (you can use Array.push()). Then - inside the find callback - .save() the updated Person.

[*] Hint: This may be tricky if in your Schema you declared favoriteFoods as an Array without specifying the type (i.e. [String]). In that case favoriteFoods defaults to Mixed type, and you have to manually mark it as edited using document.markModified('edited-field') (http:mongoosejs.comdocsschematypes.html - #Mixed )

• 9. New Update : Use findOneAndUpdate() -

Recent versions of mongoose have methods to simplify documents updating. Some more advanced features (i.e. prepost hooks, validation) beahve differently with this approach, so the 'Classic' method is still useful in many situations. findByIdAndUpdate() can be used when searching by Id.

Find a person by name and set her age to 20. Use the function parameter personName as search key.

Hint: We want you to return the updated document. In order to do that you need to pass the options document { new: true } as the 3rd argument to findOneAndUpdate(). By default the method passes the unmodified object to its callback.

• CRU[D] part IV - DELETE

• 10. Delete one Person -

Delete one person by her -id. You should use one of the methods findByIdAndRemove() or findOneAndRemove(). They are similar to the previous update methods. They pass the removed document to the cb. As usual, use the function argument personId as search key.

• 11. Delete many People -

Model.remove() is useful to delete all the documents matching given criteria. Delete all the people whose name is "Mary", using Model.remove(). Pass to it a query ducument with the "name" field set, and of course a callback.

Note: Model.remove() doesn't return the removed document, but a document containing the outcome of the operation, and the number of items affected. Don't forget to pass it to the done() callback, since we use it in tests.

• C[R]UD part V - More about Queries

• 12. Chain Query helpers -

If you don't pass the callback as the last argument to Model.find() (or to the other similar search methods introduced before), the query is not executed, and can even be stored in a variable for later use. This kind of object enables you to build up a query using chaining syntax. The actual db search is executed when you finally chain the method .exec(), passing your callback to it. There are many query helpers, here we'll use the most 'famous' ones.

Find people who like "burrito". Sort them alphabetically by name, Limit the results to two documents, and hide their age. Chain .find(), .sort(), .limit(), .select(), and then .exec(), passing the done(err, data) callback to it.

var queryChain - function(done) { var foodToSearch - "burrito";

• Well Done !!

• You completed these challenges, let's go celebrate !

• Further Readings...

If you are eager to learn and want to go deeper, You may look at :

• Indexes ( very important for query efficiency ),
• PrePost hooks,
• Validation,
• Schema Virtuals and Model, Static, and Instance methods,
• and much more in the mongoose docs