Getting More from Mongoose

In the last video, we saw how to connect MongoDB with Mongoose, 0:00 how to create schemas to represent the data we want to save, and 0:04 how to create models to save and retrieve documents from the database. 0:08 Let's take a look at some ways we can extend those tools to make 0:12 working with the data more convenient. 0:17 First let's clean up our sandbox a little. 0:20 There's a method we can call on the animal model that saves a batch of 0:23 documents in the database, create. 0:28 We can pass the create method an array of models or objects or a mix of the two. 0:32 We'll do exactly that, 0:37 create an array of a mix of JavaScript object literals and models. 0:39 Let's see this in action by creating an array of a few more animal 0:44 objects called animal data. 0:48 Let's create a mouse, Who's gray, 1:03 Who weighs 0.035 1:19 kilograms called Marvin. 1:23 A nutria, 1:37 Who's brown, Who weighs, 1:45 6.35, Whose name is Gretchen. 1:56 A wolf, Which is gray, 2:12 weighing 45 kilograms, 2:21 named Iris. 2:27 And finally, the three existing models, 2:30 elephant, animal and whale. 2:36 We can use this array to store them in the database. 2:40 Notice there are no size properties on these objects. 2:46 In fact, let's delete them from our other animals. 2:49 And we can remove the default value from our schema. 2:59 We'll see how to add this property back on dynamically in a moment. 3:08 For now, we can delete the three animal save calls, 3:13 and replace it with one create call on the animal model. 3:17 We can pass in our array of animal data. 3:36 And the callback has an error, and then the animals that were saved. 3:43 Let's remove these extra closing brackets that we don't need anymore and 3:51 clean up our code a little. 3:57 Much nicer. 4:14 Now let's see how to set the size property of each animal 4:17 dynamically before saving them to the database. 4:21 Mongoose offers us something called a pre-save hook. 4:25 This is an opportunity to do something to a document before it is saved. 4:29 We can take advantage of this opportunity by writing Mongoose specific middleware, 4:33 passing it into the pre method on a schema. 4:40 Let's implement a prehook middleware on AnimalSchema. 4:49 The handler we're passing into as the second parameter will execute 5:15 before Mongoose saves the document to the database. 5:19 It takes a next parameter that will be used in the same way as in Express. 5:23 Once we're done with our code, we can call next to tell Mongoose we're done. 5:27 Inside this handler, 5:38 the this object will point to the document or model to be saved. 5:40 Let's use this handler to examine the mass of an animal. 5:46 We can assign the size property based on the mass. 5:56 If the mass is greater than or equal to 100, 6:01 This size is big. 6:11 If the mass of the animal is greater than or equal to 5 or, 6:23 Is less than 100, Then its size is medium. 6:32 Finally, if it's anything else, it's small. 6:49 To test this out and see the results, we can alter the query we had below. 6:57 If we pass in an empty object as the first parameter, 7:07 the query will return all objects. 7:11 Then, inside the callback, we can log each animal's size so 7:16 that we see that it was set. 7:20 Now if we save this, switch over to our terminal and run our file, 7:38 we should see that the sizes are assigned correctly in the output. 7:44 As you can hopefully see, pre hooks can give you a lot of power. 7:59 Save isn't the only event that has pre hooks. 8:05 You can find out more about them in the documentation linked in 8:09 the teachers notes. 8:12 Let's see how to use this size property in a custom query called a static method. 8:23 A static method is a custom function we can call on the model directly 8:28 to help us access our data in custom ways. 8:33 For example, what if we often find ourselves needing to find small animals? 8:36 We could write the query every time, or to save some typing and 8:43 dry up our code, we could put the query into a static method. 8:47 On the animal schema, there is a statics property. 8:58 This is where we can define our static methods. 9:04 Let's create a static method on the animal model called findSmall. 9:08 We're passing in a call back here, so it can plug into the query inside 9:25 the function to preserve the flow of our overall application. 9:30 This inside the static method refers to the model. 9:49 In this case, it will equal the animal. 9:53 We can use this model to query the collection of 10:04 documents with the size property of small. 10:08 Let's update our query to see the results of the static method. 10:12 Now when we run this file, we should see our mouse and fish. 10:30 Let's generalize this method. 10:43 Instead of just small animals, let's enable this method to work for 10:46 any size we specify. 10:51 To do that, we can change the function to be called, findSize and 10:53 pass in and arguments as the first parameter. 10:58 And then modify the query object to include the size too. 11:07 Down at our query, change findSmall to findSize. 11:19 With the first argument, medium. 11:25 I'll let you test that out on your own, if you'd like. 11:33 Static methods can be really helpful 11:36 when we want to create custom queries from the perspective of the model. 11:39 But what if we wanted to find data based on a document that we already have? 11:43 For example, what if we want to find an animal, and 11:48 then we want to find more animals with the same color? 11:51 We can use instance methods for this. 12:01 Instance methods exist on all documents. 12:04 In instance methods, the this value points to instances of the document itself. 12:07 To create an instance method, we'll first place 12:14 a function on AnimalSchema's methods property. 12:19 Let's call our method findSameColor. 12:25 To get a reference to the model, we can call the document's model method and 12:48 pass in the name of the model we wish to access as a string. 12:53 In this case, it's animal. 13:06 From there we can query the usual way. 13:09 Passing in the documents color with this this.color. 13:12 To see this in action, we'll need to modify our query once again. 13:31 Let's use the Animal model's findOne method to retrieve an elephant 13:36 This method will search the database for 13:54 batches and whichever is first to match is the one returned. 13:57 This is good if you only want one matching document in the database. 14:02 We can use the resulting document to call the instance method and 14:07 print out the results to the console. 14:11 Now when we check the results in our terminal, 14:57 we see we get all the gray animals. 15:01 Success, now that we've seen how to use static and instance methods 15:04 to customize the way we handle database interactions with Mongoose. 15:10 We've also seen how to implement a pre save hook. 15:14 There are other features Mongoose offers, and I'd encourage 15:17 you to read the documentation linked in the teacher's notes. 15:21 Feel free to play around in the sandbox, too. 15:24 When you're ready, we'll start integrating Mongoose into our Express app. 15:28