Lecture 278:- Fetching Data from DB

To fetch data from MongoDB using Mongoose, we can make use of the find() method of the Model class. The find() method allows us to query the database and retrieve documents that match the specified criteria.

Here's an example code snippet that shows how to fetch all documents from a collection:

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const mongoose = require('mongoose'); const { Contact } = require('./models'); mongoose.connect('mongodb://localhost/my_database', {  useNewUrlParser: true,  useUnifiedTopology: true, }); // Fetch all contacts Contact.find({}, (err, contacts) => {  if (err) {    console.error(err);    return;  }  console.log(contacts); });

In the above example, we first establish a connection to the database using mongoose.connect(). Then, we call the find() method on the Contact model to retrieve all documents from the collection. The first argument to find() is an empty object, which means we want to retrieve all documents from the collection. The second argument is a callback function that will be executed when the query is complete. If an error occurs during the query, we log the error to the console. If the query is successful, we log the retrieved documents to the console.

We can also use various options with the find() method to filter and sort the retrieved documents. Here's an example that shows how to find all contacts whose first name is "John":

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// Fetch contacts with first name "John" Contact.find({ firstName: 'John' }, (err, contacts) => {  if (err) {    console.error(err);    return;  }  console.log(contacts); });

In the above example, we pass an object with a firstName property to the find() method. This will retrieve all documents from the collection where the firstName property is equal to "John".

We can also use the sort() method to sort the retrieved documents. Here's an example that shows how to retrieve all contacts and sort them by last name:

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// Fetch all contacts and sort by last name Contact.find({})  .sort({ lastName: 'asc' })  .exec((err, contacts) => {    if (err) {      console.error(err);      return;    }    console.log(contacts);  });

In the above example, we call the sort() method on the query object returned by find(). The argument to sort() is an object that specifies the sorting order. In this case, we're sorting by the lastName property in ascending order. Finally, we call the exec() method to execute the query and retrieve the documents. The callback function will be executed when the query is complete, and we log the retrieved documents to the console.