The Express. js Course - Module 6: CRUD Operations with Mongoose

1. Class Introduction: Welcome back to Module six of the ExpressJcurse, credit operations with Mongoose. This is a continuation class of the Express JS course series. My name is Shawn aguanhi, you are instructor for this exciting journey into the world of Mongo Dew and Mongoose. Having built numerous data driven applications, I can tell you that mastering Mongo Dew is an essential skill for modern Bend developers, and mangos makes it incredibly powerful and intuitive. In this module, we are diving deep into Mongo DB and mangos. Here's what you will learn how to connect your NurJs app to MongoDB designing efficient and flexible data schemas with mangos. And then creating, reading, updating, and deleting data using mangos models, mastering advanced queries, including operators, logical conditions, and regular expressions. After that, you'll learn implementing features like pagination and counting documents. And finally, you will explore the best practices for managing and upgrading your database. This class is perfect for developers who want to integrate Mongo DB into their no JS applications. If you have completed the earlier modules on restful ABIs and Express Js, we are all set to begin. No prior experience with MongoDB is required. We will start from the basics and gradually advance to more complex topics. By the end of this module, you will have the skills to build robust data driven applications. Whether you are creating a small personal project or large scale production app. MongoDB and Mongoose will give you the flexibility and efficiency you need to succeed. Finally, in this module, our project is built around a standalone application called Mongo Demo. This project includes three focused exercises where you will design mongoo schemas and models to structure your data effectively, write and execute crowd operations to manage data dynamically, and implement advanced techniques like query filtering, pagination, and updating documents using industry standard patterns. These exercises will help you build confidence in working with Mongo Deb and mangos, preparing you to handle complex data operations in real world applications. I can't wait to help you master Mongo Di Bi and mongoose. Let's dive in and get started. See you in the first lecture. 2. Getting Started with MongoDB: Alright, so back to our Fairwheels application, so far we have stored the list of companies in an array in memory. That's not how we build real world applications because when the server restarts, we're going to lose all the data in memory. So that's why we need to store our data in a database. Now, as I told you before, when building applications with Node and Express, you have a large number of options in terms of the database you want to use. In this course, we are going to use Mongo DB because that's a very popular database management system, and it's quite often used in applications built with Node and Express. So if we have never worked with Mongo DB before, don't worry. You're going to learn about it bit by bit or the next few sections. Now, just to set the right expectation, Mongo be really requires its own course. So you're not going to be a Mongo Be expert by the end of watching this course, but you're going to learn enough to get the job done. Now, if we have never worked with Mongo DB before, Mongo DB is basically what we call a document or no SQL database. It's different from traditional relational databases like SQL server or MySQL and so on. So in Mongo B, we don't have the concept of tables, schemas, views, records, columns. It's different. So unlike relational databases, where you have designed your database ahead of time, in Mongo DB, there is no such a thing as schema or design. Simply store your JCN objects in Mongo DB. So here we have an array of companies. We can simply store all the objects in this array and a collection in Mongo DB, as simple as that. This also means when quering our data, we get JCN objects out of Mongo DB, and we can simply return those objects back to the client. So there is no transformation. That's enough introduction about Mongo DB. Next, I'm going to show you how to install it on your machine. 3. Installing MongoDB for Node.js: In this lecture, I'm going to show you how to install Mongo DV on Windows. So open up your browser and head over to mongodv.com. On this page, on the top left, click on product, and then here, select the option Community Addition. This is the Mongo DV server that we run on this machine. Scroll down, check the version, and make sure Windows is selected. Now download this MSI. So let's save this. All right. And now let's run it. Click on install anyway. So this gives us a very simple installer. Let's go ahead. Next, accept the license agreement. Next, and do a complete installation. Again, next, now on this page, there is a checkbox here. Install MongoiVKmpas. This is the client application data we use to connect to our MongoDB server. We look at our databases. Next, install All right, Mongo DB is installed. And our Mongo DB compass is also launched, we'll talk about it later. So now let's open up File Explorer and go to Program Files, and then Mongo DB. Next server. Now, the version I'm running is 7.0. Chances are, in the future, when you're watching this, the version will be different. So select that folder and then Ben and then finally Mongo D. There is Mongo Damon, which is a service that runs in the background. And that's basically our Mongo DB server. Now, what I want you to do is select this path here. Now in the search bar, search for advanced system settings. On this page, we need to go to environment variables here. And then from this list of system variables, select Path, click Edit, and then new. And here we pace the path that we copied earlier. This is the path to the directory that contains our Mongo DV server. Okay? Now on this page, also select Okay. Jan. Now open up PowerShell and run Mongo D. If you don't see this output and get an error like Mongo D is not recognized, you need to restart Power Shell. So close all the PowerShell windows that are currently open on your machine and then open it. So when you run Mongo D, you should see an output like this. By default, you are going to get an error. So here, look, we get this exception, non existent path data directory, C, column backslash data backslash TV not found. So by default, Mongo DV stores your data in this folder. So let's create this folder. MKDIR, C colon backslash data, backslash TV. Okay. Now let's run Mongo E one more time. This time we don't get that exception. And the last message is waiting for connections on port 27017. So this verifies that Mongo DV server is running. Now we can go to Mongo DV Compass. So here's the page to get started. That is connect to host. We need to specify the Mongo DV server we want to connect to. So leave the default values as they are. So the host name is local host and port is 27017. Now, let's connect. Beautiful. We are successfully connected to our Mongo DV server. So here by default, we have three databases, Local, Armin and Config. These are for MongaTV to do its job. We are not going to work with these databases. 4. Connecting Node.js to MongoDB: Alright. Now let's create a new project for this section. So I'm going to create a new folder called Mongo Demo. Let's go in this folder and run NVM in it with a US flag. Beautiful. Now we need to install a knot package called Mongoose. Mongoose gives us a simple EPI to work with a Mongo DB database. Okay, so you can see at the time of recording this video, I'm using Mongos version 7.5 0.0. So if you want to make sure you have the same experience as what I'm going to show you in this video, I highly encourage you to install the exact same version. Alright, let's add a new file here, index dot JS. The first thing we need to do is to connect to Mongo Deb. So we'll load this mangos module. And store it in the constant pongos. Now, this object has a method called connect. We use this to connect to Mongo DB. Now here we pass a connection string that is Mongo DB, Allan 127.0 0.0 0.1. Column 27017. This references the Mongo DV that we installed on this machine. When you want to deploy your application to a production environment, you are going to have a different connection string for the production. Earlier in this section about Express, I told you how to manage various configuration settings for different environments. In this video, we are not dealing with that level of complexity. So I've hard coded a connection string here. But in real application, your connection string should come from a configuration file. So here's our Mongo DB server. Now, after that, we add the name of our database. In this case, I'm going to use a simple playground database. Now we have not created this database, and it doesn't matter. The first time we write something to this database, Mongo E B will automatically create this database for us. Okay, so this is how we connect to a Mongo I B database. Now, this connect method returns a promise. So we can call then when this promise is fulfilled. That means we have connected to a Mongo Eb database. So here we can do a simple console dot log connected to Mongo I B. And by the way, here I'm using Tensole dot log for simplicity. As I told you in the section about Express, in a real application, it's better to use the debug module because with that, you have more control over how much of these debugging messages you want to see. But in this section, we don't want to get distracted with too much complexity. We just want to focus on Mongo DB. So this is for scenario where we successfully connect to a Mongo IB database. But what if something goes wrong? We want to catch that error. Here, we get an error object and then display it on the console. So console dot error. Connection to MangiIBFail. And then we add the error object. Beautiful. Now, let's run this application. So back in the terminal, North moon index dot JS. So we can see we are successfully connected to Mongerib. 5. Designing Data Schemas with Mongoose: So we have connected to our Mongo DB database. Now the next thing we need to do is to create a schema. We use a schema to define the shape of documents within a collection in Mongo DB. What do I mean by that? Well, let's go back to our Mongo DB compass. I've created this database here, ground. And in this database, we have this collection called courses. A collection in Mongo DB is like a table in a relational database. Now in this collection Curses collection, we have three documents. A document in Mongo IB is kind of similar to a row in a relational database. So in relational databases, we have tables and rows. In Mongo DB, we have collections and documents. Now let's take a look at this collection. So here's an example of the document. Each document is a container of key value pairs. So here we have underline ID, which is a unique identifier. For each document, we have tags, which is an array of key value pairs. We have name, author, is published, date, and version. Now, don't worry about how I created this. You are going to learn that over the next few lectures. Now in Mongoose, we have this concept called schema. This is just specific to mongoose. It's not a part of Mongo DB. We use a schema in mongoose to define the shape of documents in a Mongo DB collection. So we use that to define what are the properties we have in this document. Now let me show you how to create a schema. So back in VS code, let's define a constant, call it course schema. This schema defines the shape of course documents in our Mongo DB database. So we set this to a new Mongoose schema class. Here, when creating an instance of this class, we pass an object. And in this object, we specify the key value pairs that we should have in course documents. So you want each course to have a name property, and the type of this property should be a string. Similarly, each course should have an author of type string. I want our courses to have X. And here, I want to have an array of strings. Not technically when this is stored, each object in this array will be a key value pair. The key will be the index and the value will be that string. Now also I want each course to have a date property of type date. Now we can also give this a default value, so we can change this from date to an object. This object is a type property that we set to date, and it also has a property called default, and we set this to date dot now. With this, we don't have to specify a date when creating a course object. Date that now will be used as a default value for this property. And finally, I want each course to have a property called I published, which would be a Boolean. So here's the list of types we can use when creating a schema. We have string, number, date, buffer, which we use for storing binary data, boolean, object ID, which is used for assigning unique identifiers and array. Next, I'm going to show you how to create and save a document based on the course schema. 6. Creating and Using Mongoose Models: So here's our course schema that defines the shape of course documents in a Mongo De database. Now, we need to compile this into a model. What is a model? Well, earlier in the course, I talked about the concept of classes and objects. So as an example, I told you that we can have a class called human, we can have an object like Shen. So an object is an instance of a class. A class is just a blueprint, but an object is an instant of that blueprint. Now in this application, we want to have a class called course. And then we should be able to create instances of that class, like a node course. And then we can save that node course to our database. So to create a class like course, we need to compile this schema into a model. So this is how we do this. This mongoose object that we have has a method called model that takes two arguments. The first argument is the singular name of the collection that this model is for. So in our Mongo EB database, you want to have a collection called courses, right? So here's a singular name course. The second argument is a schema that defines the shape of documents in this collection. So that is course schema. Now with this, we get a course class in our application. So we can set this to a constant called course. And note that here I'm using paceal naming convention. So the first layer of course is uppercase, that means this is a class. It's not an object. Now we can create an object based on this class. So let's create a course object. And here, I'm using camel case notation because the first letter of the first word, in this case, course is lowercase. So we use Camel case to name our objects and pacelcase to name our classes. So this course, we set this to a new course, and in this constructor function, we pass an object, we initialize our course object. So let's set the properties of this course. I'm going to set the name to the Express JS course. Set the author to Shiv in. Set the text to an array of two strings. So we can have Express and let's say back in. Now this is an interesting thing about mango or no SQL databases in general. You can see that a document in Mongo DB can be a complex object. So here, this tag property is an array of strings. We don't have something like that in relational databases. In other words, a row in a relational database has simple attributes. If you want to model this structure in a relational database, you need three tables courses, tags, and an intermediary table called course tags because here we have a many to many relationship between courses and tags. Mongo IB or no SQL database in general, we don't have this structure. We don't have to define these tables. We don't have to script them. We simply create our objects and store them in a database. That's why we call them schema less. They don't have schema. So here's our tax property. Now the other property we have is date. But earlier, I defined this to have a default value. So I'm not going to set this here, and the last property is published. I'm going to set this too, true. So let's quickly recap. Once we have a schema, we need to compile that into a model, which gives us a class. Next, we can create an object based on that class. And this object maps to a document in a Mongo DB database. Next, I'm going to show you how to save this document in our database. 7. Persisting Data with Mongoose: All right. So here's our course object that maps to a course document in Mongo DV. Now, let's save this to our database. So this course object has a method called save. Now here we are dealing with an asynchronous operation because it's going to take some time to save this course in the database because we are going to access the file system. That's why we are dealing with an asynchronous operation. The result of this operation will be ready in the future. So this method returns a promise. We can aviate it and get the result. This result is the actual course object that is saved in the database. So when we save this course in Mongo DB, Mongo DB is going to assign a unique identifier to this course object with this course document. Now with this, we can see the IRE that is assigned by Mongo DB. So let's log it on the console result. As I told you before, whenever I use a weight, your code should be inside an async function. So I'm going to define a function here, st, create course. We set this to a sync error function like this and put all this code inside this function. So we create a course object, save it, and then display the result on the console. And finally, here we call create Curse. Save. Now, back in terminal, in this section, I'm going to run this application using Node instead of norm because with no one, every time I make a simple change in the code, that will result in creating a new document in our Mongo DB database. So node index dot js. Beautiful. Our course was saved in the database, and here's the document that is actually stored in our Mongo DB. Look, Mongo DB assigned this property underline ID, and it is set to this unique identifier. Now let's go back to Mongo DB compass. So let's refresh here. Here's our playground database. We have this courses collection, and in this collection, we have one document, right? So this is a beauty of Mongo DB or nose EQUL databases. Unlike relational databases, we didn't have to create a table. We didn't have to script that table. Simply created a document and stored it in our Mongo DB datas. So back in the board, let's modify these values and create another document. Because in the next lecture, I'm going to show you how to query documents. So let's change this to the ReactJS course, and we add two tags, react dot js and front end. Save. Back in the terminal, let's stop this process and run this application again. Here's our second document. And if you look in MongoiVKmpas, let's refresh the result. Look, we have two documents in our courses collection. Beautiful. So next, I'm going to show you how to query documents. 8. Mastering Mongoose Queries: All right now, let me show you how to drive documents from a Mong Wo DV database. So here, I'm going to create another function Pas G courses. We said this to Async error function. And then I'm going to replace the call to create course with G courses. Now, let's implement this function. So this course class that we defined earlier has a bunch of methods for quering documents. We have find to get a list of documents. We have find by ID, which is pretty self explanatory. And we have find one, which returns a single document. Now we have a few more fine methods here, but don't worry about them. We use them to find a document and then to remove or update it. We are going to look at them later in this section. So let's look at fine method. As you can see, this method returns a document query option. Now this document query object is kind of like a promise. So it has a then method, so we can avid it and get the result. And with this, we get all the courses in our database. So let's display it on the console. Now back in terminal node index to Js. So look, we get an array with two objects. Here's our first course, that's the express ts course, and here's the second course. That's the react to Gs course. Beautiful. Now we can also pass a filter here. So as the first argument to the fine method, we pass an object, and in this object, we add one or more key value pairs for filtering. So let's say we want to get only the courses from Shevn. So we set author to Shevn we can pass another property. Another filter is published through. So with this filter, we only get the published courses per sewn, and this is how we arrive documents. But here we can also sort our documents. We can set a limit on the number of documents that are returned. We can also select specific properties in the document. Let's say our course documents there 50 properties, maybe we don't want to return all these properties to the client, perhaps you want to return only their name. So let me show you how to build a more complex query. Earlier, you saw that this fine method returns a document query object. Look, document query, right? So here we can customize this query. We can apply a limit. Let's say, we can sort the documents. Here we pass an object. And in this object, we add one or more key value pairs for sorting. So let's say we want to sort these documents by their name. We set name to one. One indicates ascending order. We want to sort these documents in a descending order, you use minus one. As I told you, you can have multiple key value pairs here. We also have another method select, and with this, we can select the properties that we want to be returned. For example, let's say we only want to get the name and the tax property of each course document. So we set name to one and text to one as well. Now let's run this application, back in terminal node, index Js. So look, now the course objects that we get have only three properties. Tag the name, we selected these two properties, but we also get the underlying ID property that is assigned by Mongo DB by default. Also, these documents, they are sorted by their name in descending order. So the react GS course comes first, even though we created this course later. So this is how we build queries. In the next lecture, I'm going to show you how to do more complex filtering. 9. Mongoose Query Comparison Operators: So in the last lecture, you learned how to use the fine method to filter documents. Or the next few lectures, I'm going to show you how to build more complex queries. Now, if you have never worked with Mongadb before, you will find the syntax we use to build queries, a little bit unfamiliar or strange, and I totally understand that because I have been there before. But in this lecture, I'm going to show you a technique remember this syntax, and then you will realize it's actually very easy. So the topic for this lecture is comparison operators. So in Mongo DV, we have a bunch of operators for comparing values. Since mongoose is built on top of Mongo DV driver, these standard operators that Mongo Dee understands, they are also available in mongoose. So here are the comparison operators that we have in Mongo DB. We have EQ, which is short for equal, we have NE, which is short for not equal. We have GT, which is short for greater than we have GTE, which is short for greater than or equal to. Similarly, we have LT, which is short for less than. We have LTE, which is short for less than or equal to. We also have N and NIN, which is short for not N. Now, for the purpose of this lecture, let's imagine our courses have a price property. I'm going to comment out this fine method. Let's say we want to get all the courses that are $10. How do we do this? So we call fine, pass an object for filtering, set the price to ten, so this returns only the courses that are $10. Now, what if we want courses that are more than $10? How can we express this using JCN objects in JavaScript? Well, you know that in JavaScript, an object is basically a collection of key value pairs. So here, our key is price and our value is ten. With a simple value, we cannot express a concept of more than or greater than ten. So in order to express the concept of greater than ten, we need to pass an object. Here, this object is again a container for key value pairs. Now here, I can use one of these operators as a key. Let me use greater than operator here. Do sine will indicate that this is an operator. GT that is greater than, and we set this value to ten. So see what I did. I replaced a simple value like ten with an object to express a concept, the concept of greater than ten. Now we can change this operator to greater than or equal to. If you want courses that are $10 in the result as well. Let's take this to next level. What if we want to get the courses that are $10-20? Again, we can use another operator, so less than or equal to $20. So this is how we can use these comparison operators to query documents. Now let's look at another example. Let's imagine we want to get courses that are $10 or $15 or $20. So I'm going to commend this out. Let's start from scratch. So we call find, pass an object for filtering, set the price again. If I use ten, I can only compare equality to ten. We don't want that. We want courses that are either $10 or $15 or $20. So we replace this value with an object to express our query. Now here, we use an operator that is dollar in. Now, what would we use for the value? Here, we want to express a query where courses are either $10 or $15 or $20. So we are dealing with three values here. What Javascript construct do we use to express multiple values? We use an array, right? So ten, 15, 20. See what I've done so far. I haven't memorized anything. I just try to logically think, how can we use how Script constructs to express a concept to express a query. So these are the comparison operators. And the next lecture, we're going to look at the logical operators. 10. Logical Operations in Mongoose Queries: In this lecture, I'm going to show you how to use the logical query operators. So here's our original query. We're getting all the courses that match this criteria. They are authored by Shevin and they are published. What if we want to get the poses that are published by Shevin or the courses that are published? So we can have courses that are published, but they are not authored by Chevan. That's where we need the operator. So here are the logical operators we have. We have R and M. See how we can use these operators. So I'm going to commend this out. Instead, we're going to call the fine method without any filters. After that, we call the R method. Now, here's a question for you. What Java strip construct do we use to store multiple values? We use an array, right? So here we need to pass an array, and in this array, we add two objects. Each object is a filter, just like the filter object that we pass to the fine method. So in this first filter object, we add author. We set this to Shi in a second, we add this published, and we set that to true. Now with this, we'll get courses that are authored by Shevin or courses that are published. The N logical operator is exactly the same. But instead of using the method, we use the method. And with this, we pass an array of filter objects. Now this is technically similar to passing a filter object to the find method. But sometimes in more complex queries, you may find a place for using the N method. Next, we're going to look at regular expressions. 11. Harnessing Regular Expressions in MongoDB: So back to our original query, in this example, we're getting courses whose author is exactly the string. Here, if we have a course with authors such as Shevin or Shevin a Guanhi, those courses will not be returned. So if you want to have more control over filtering strings, you need to use a regular expression. Let me show you how that works. So I'm going to comment this out. Let's say we want to get courses whose author starts with Chewn this is how we write this query. So find as an object, set the author. Now instead of passing a string here, we pass your regular expression. So we add a slash, we add a pattern that we are going to modify in a second, and another slash. So this is a syntax for representing a regular expression. Now in regular expressions, we can use this carat character to represent a string that starts with something. Here, I can add Shen. So this regular expression represents a string that starts with Shen. So as long as the other starts with Shen, it doesn't matter what we have. Those courses will be retired. Now, what if we want to look for courses whose author ends with a given string? Let's say ends with Ragan G. So this is how we write this query. Fine, as an object, we set the author to a regular expression to slash pattern. And the pattern we use here is Rugen hi Dasg. A doll sine in regular expressions indicates the end of a string. So here we are looking for courses whose author ends with abonci. Now, this query is case sensitive. If you want to make it case insensitive, you append an I at the end. And finally, let's look at the last example. What if you want to look for poses whose author contains the word ship? So shift can be at the beginning. It can be in the middle, or it can be at the end. So let me show you how to write this query. So we call fine as an object, author, regular expression. Here's our pattern. Dot, star, shift dot star. So that star in a regular expression means we can have zero or more characters. We don't care what those characters are. So with this pattern with this regular expression, we can have zero or more characters before or after shift. And once again, if you want to make this case insensitive, we put an I at the end. Of course, you can use more complex regular expressions. The explanation of JavaScript regular expressions is beyond the scope of this course. So if you want to learn more about regular expressions, just read a tutorial about JavaScript regular expressions. 12. Implementing Pagination with Mongoose: So in this query, you are filtering our courses and picking only their name and tax properties. So if you run this application, this is what we get an array of two courses. And each course has these three properties. Sometimes we just want to get the number of documents instead of the actual documents. So if that's the case, we don't need to use select method. Instead, we call count, and this returns the count of documents that match this criteria. So back in terminal, let's run this application again. Look, we have two documents that match our filter. 13. Mongoose Update Patterns: Query First Approach: So earlier you learned about this limit method. A method that goes hand in hand with the limit method is a skip method. And we use this to implement pagination. Let me show you how this works. So let me define a constant called page number. This can be one, two, three, whatever. So let's set this to two. We have another constant called page size. Yeah. So I've hard coded these numbers. That's purely for simplicity. But in a real world application, we pass these values as query string parameters to restful APIs. So you might have an API to get the list of courses. It's endpoint can get query string parameters like this. So page number, we set this to two and page size, we set this to ten. This is how it works in the real world. For now, we don't have to worry about this. So let's delete this. In order to implement pagination, we need to skip all the documents in the previous page. So here's the formula. Page number minus one times page size. So here, I'm assuming page number starts from one. So more accurately, this is page number, not page index. Okay? And then we change limit to page size. With this, we can get the documents in a given page. 14. Mongoose Update Patterns: Update First Approach: So you learned a lot about queering documents. In this lecture, I'm going to show you how to update documents in Mongo DB database. So let's create a new function. So last update course. We set this to an error function and it should take an ID. So as ID, fed R goes to a coord block. This is the ID of the course. We're going to update it, and then here, we're going to replace this with update course. Now there are basically two ways to update a document in MongaiV. One approach is what I call where you first. So you find a document using Fine by ID, then we modify its properties. And then finally, call the save method. This is probably the approach that you have used in other frameworks. Now the other approach is what I call update first. So instead of retrieving a document first, we go in the database and update directly. Now we can often get the updated document as well. So in this lecture, I'm going to show you the first approach, and we'll look at the other approach over the next video. So let's delete all these comments. Here we want to get the course with a given ID. So course dot Fine By ID, we pass this ID here. Now, this returns a promise, so we away it, get the result and store it here. Now, chances are there is no course with a given ID, so we need to check for that. If we don't have a course, we are going to return immediately. Otherwise, we are going to upgrade the properties of this course. So we can set course dot is published to true and also author to another author. There is another approach. Instead of setting multiple properties, we call the set method. So course dot set. Here we pass an object with key value pairs to be updated. So we can set is published to true and author to another author. So basically, these two approaches are identical. Which one you choose is purely your personal preference. Now in this demo, I'm going to use the first approach, and finally, we call the save method. This is the same method that we used earlier, create a new course. So it returns a promise. We can awate it, get the result, and display it on the console. So console dot log result. Now I'm going to go back encompass and get a valid course ID. All right. So here in our courses collection, I'm going to grab this course ID and paste it here. Now, back in terminal, let's run this program. Here's the course that we updated. Look, author is set to another author. In the next lecture, I'm going to show you how to update a document directly in the database without retrieving it first. 15. Counting Documents with Mongoose: I in the last lecture, you learned about the query first approach to update a document. This approach is useful if you receive an input from the client and you want to make sure that the update is a valid operation. For example, here we have a business rule. So if the course is published, maybe we should not be allowed to change its author. To implement this business rule, we need to retrieve the course first, and then we need to write some logic like this. So if course is published, we want to return. We don't want to update this course. So that's when we use the query first approach. But sometimes, you know what you are doing, you are not receiving input from the client. You just want to upgrade document or perhaps multiple documents directly in the database. And that's what I'm going to show you in this lecture. So instead of using the fine by ID method, we use the update many or update one method. Now, the first argument here is a query or a filter object. So we can get the course with this ID, or we can pass something more generic. We can get all the courses that are not published. So with this, we can update multiple documents in one go. Now in this demo, we want to update a course with a particular ID. I'm going to change this to underline ID and set this to ID argument. Now the second argument to the update one method is the update object. Now here we need to use one or more of the Mongo DB update operators. So if you search for Mongo DB update operators, On this page, you can find the list of all the supported operators. So we have current date to set the value of a field to the current date. We have ink or increment. This is very powerful. With this, we can increment the value of a field by the specified amount. Imagine you want to build an application like Facebook. So when the user likes a post, you want to increment the number of likes. This operator, you can increment the number of s directly in the database. You don't have to retry the post first, then increment the number of s. You can also pass a negative value to decremente the value of a field. We have men which is useful if you want to update a field if the specified value is less than the existing field value. We have another similar operator, and with this, we can update a field if the specified value is greater than the existing field value. We have L or multiply, which is kind of similar to increment. But with this, we can multiply the value of a field by the specified amount. We have set, which I'm going to show you in this lecture, and with this, we can set the value of field. And similar to this, we have set, which we can use to remove the specified field from a document. So back here in our update object, I'm going to use the set operator. We set this to an object, and in this object, we add one or more key value pairs. So let's say we want to upgrade the auor property, set it to Shevin, and we want to set is published to falls. So with this update one method, we can update a document directly in the database without retrieving it first. Now, what we get here is the result of the update operation, not a course object. So let's rename this to result. Now we don't have to check for the existence of a course. We don't have to update the properties here, and we don't have to save it explicitly. Okay, very simple. So let's go back in the terminal and run our application again. So you can see here in the results object, we have modified one document. And here is this document in our Mongo DV database. So author is set to Shiv in and is published is set to false. Beautiful. Now, sometimes you want to get the document that was updated. If that's the case, instead of the update one method, you need to use fine by ID and update. So here, as a first argument, we need to pass an ID instead of a query object. And similarly, as the second argument, we pass our update object. Now, what we get here is a course object. So I'm going to change the author to Shevin and is published to True. Let's run this program and see what happens. So node, index or Js. All right, here's the course document that we updated. However, look, the author is still shivn and is published is false. So what we get here is the original document that is the document before the update operation. If you want to get the updated document, you need to pass an option. We need to pass another argument to this method. Here I pass an object and set the new property to true. And with this, we'll get the updated document, save. Now, back in the terminal, let's run the application again. Okay, look, Author issuing and is published is true. So with this method, we will send one command Mongo Dev to update document and return it. Next, I'm going to show you how to remove a document. 16. Removing Documents in Mongoose: In this lecture, I'm going to show you how to remove a document. So to save time, I'm going to get the port for the update course function, duplicate it, and then rename this to remove course. And finally, replace this with remove purse. All right. Now let's implement this function. So to delete a document, we call course. Here we have this method, delete one. This method takes a filter or a query object, so we can pass an object like this. And with this query object, we can find a document with a given ID. Now, if we send something more generic like is published, set to false, we might have multiple courses that are not published. This method, delete one will find the first one and delete it. Now in this demo, we don't want to use this. I'm going to revert this back to this query object. Now similar to the update one method. This method returns a promise, so we can away it, get the result, and store it here, and then log it on the console. Now let's run this program, so no index dot js. Okay, here's our results object and you can see that we have deleted one document. Now if you want to delete multiple documents, instead of delete one, use delete Manu. This method also returns a result object that shows the number of documents that were deleted. Now, if you want to get the document that was deleted, we have another method here. So pose dot fine by ID and remove. So you pass the ID here. This returns to promise. We await it, get the result and store it in this course object. So now I'm going to commend out this first line. And we already deleted this course. So let's run this program and see what happens. Node indexed or hs. So we get NO. So if we don't have a course by the given ID, this method will return NOP