Connecting the API and Database

[MUSIC] 0:00 We have one final thing today, connect incoming requests to the database. 0:04 This will take place inside the route handlers. 0:10 The handlers will receive the requests from the outside world and 0:13 to use Mongoose to persist or retrieve the data. 0:16 Let's connect Mongoose to the route handlers and response to requests. 0:19 In the routes file, let's start by importing our question model. 0:24 We'll require it at the top and assign it to question. 0:31 Now we'll be able to use question to create documents and query the database. 0:50 We can start with the root routes get request handler. 0:55 For this, we want the API to return all question documents. 1:01 On the question model, we can call the find method, 1:06 and pass in an empty object literal followed by a callback function. 1:12 To make sure the question objects are sorted so 1:34 that the most recent ones come first, 1:37 we need to add additional parameters to find the method before the callback. 1:39 If the second parameter is not a function, 1:45 in other words our callback function, the find method expects it to be 1:48 what Mongo calls a projection to limit the fields returned by the query. 1:53 In other words, a projection is a way to return excerpts of a document. 1:59 Since we don't want partial documents, we want full documents, 2:04 we'll pass in null as the second parameter. 2:09 And then we can specify how we'd like our ordered results as the third parameter. 2:14 Passing in an object literal. 2:21 By entering the property of sort, we can specify another 2:30 object literal with the key we want it to be sorted by. 2:35 Entering -1 means the documents will be sorted in descending order. 2:41 This means the most recent data will be at the beginning of our results array. 2:47 Without this null placeholder, Mongoose would try to 2:53 use this object as a projection. 2:57 So we need this null value here. 3:03 This tells mongoose how to sort our results. 3:05 The callback is now our fourth parameter. 3:11 In the body of a callback function 3:15 we first want to handle any errors that may result from executing this query. 3:18 So we'll need to access the next function and 3:23 hand it off to express's error handler. 3:26 If there are no errors, we can send the results to the client's request. 3:47 Because we're getting JavaScript objects back from Mongo, we can 4:02 drop them straight into the JSON method on the response object and send them out. 4:06 I want to show you a slightly different way to query the database with Mongoose. 4:11 One but you might find a little easier to use 4:16 than this full parameter method signature. 4:19 If we don't pass in a callback function to the find method, 4:22 it doesn't execute the query immediately but rather returns a query builder. 4:25 You can use this builder to modify the query with additional methods. 4:31 When you're ready to execute the query, 4:36 we can call the exec method on the builder and pass in the callback function into it. 4:38 So first, we'll call find with an empty object literal 4:43 as we did before to get all the results, then call sort on it. 4:49 And passing in that same sourcing object that we used before. 5:08 At this point the query hasn't been executed yet, 5:13 the sort method returns another query builder so 5:17 you can chain any number of modifications together through additional method calls. 5:20 This is the only one we'll need, so we can call the exec,. 5:27 And pass in our callback function. 5:36 This executes the query and calls the callback function. 5:46 If you'd like to read more about this style of building queries, 5:51 there is a link in the documentation in the teacher's notes. 5:55 The style you choose is up to you. 5:59 Now let's handle the post action for this route. 6:03 To create a new question document from the incoming JSON on the request body, 6:06 we can pass it in directly to the model constructor. 6:11 Then we can call save on it. 6:35 And pass in a callback function. 6:39 Don't forget that add in next, as this will help with errors. 6:51 We can use an HTTP status of 201 to indicate to the client that 7:10 the document was saved successfully. 7:14 Finally the document can be returned as JSON to the client. 7:24 The next handler to complete is the get request for a single question. 7:46 For this we can use the findById query method on the model, 7:52 passing in the questions ID from the URL. 8:00 Let's pass in a callback, With an error and the document. 8:15 Let's handle the error like we did before. 8:26 And return the question document to the client as JSON. 8:33 Now this is a fine way to do it but there is a better way. 8:52 Express allows us to trigger a handler whenever a URL parameter is present. 8:56 In this case, if qID exists, we can preload 9:02 the question document in the handler so it will be present on any matching route. 9:08 To do this, let's go to the top of our router file. 9:14 And on the router object, Call the param method. 9:19 The param method takes two parameters, 9:29 the name of the route parameter as a string, and a callback function. 9:32 This callback will get executed when qID is present. 9:44 The callback takes the same parameters as other middleware. 9:57 Except for the last one which takes a value from the route parameter, 10:01 in this case qID. 10:07 So first we can load the question document and if there's an error, 10:17 it will pass it forward to the error handler. 10:22 If the document can't be found, 10:31 we want to return a follow for 404 error to the client 10:34 Remember to set the status property on the error 10:49 object since the error handler will look for 10:54 that and use it if it's there. 10:59 Finally, if it exists, let's set it on the request object, so 11:08 it can be used in other middleware and route handlers that receive this request. 11:13 Finally, let's call next to trigger the next middleware. 11:26 Now, we can go back to the route handler we just made, and simplify it. 11:39 We won't need to query the database anymore because the param handler will be 11:45 doing that, so we can delete that. 11:49 And we don't need to handle the errors since the param handler is doing that too. 11:52 All we really need to do now is send out the document to the client. 11:59 Now we're ready to tackle the answers collection route. 12:17 Since we're already having the question loaded by the param method, we can 12:21 start to see here how it's relieving us from typing a query for each route. 12:26 It's just there in the request. 12:31 After getting the reference to the pre-loaded question and 12:38 accessing the collection of answers We 12:41 can simply push the object literal version of the document we want to add. 12:46 Mongoose will create the document for us. 13:07 To save it, we need to call save on the question document. 13:10 And in the callback, 13:21 We can set the http status to 201, which tells the client that their resource 13:33 was successfully created, and then send the response back to the client. 13:39 But the specific answer route, we can say that another 14:00 parameter handler would be useful here to preload answer documents. 14:04 Let's go ahead and make that now. 14:10 Under the parameter handler for qID, we can create a similar handler for 14:28 the answers using the aID parameter. 14:34 Mongoose has a special method on sub documents array called ID. 14:45 The ID method takes an ID of a sub-document, and 15:02 returns the sub-document with that matching ID. 15:05 If the answer can't be found, We want to send a 404 error. 15:22 Otherwise, we'll call next to pass control back to the router. 15:36 Now that the answer is loaded, let's use it in our put route, 15:56 we can use the update instance method. 16:00 Remember, we'll pass in an updates objectm which will contain the properties and 16:15 values we want to modify on our existing document. 16:21 In this case, it's the requests body. 16:25 Then a callback to fire, after saving the updates to the database. 16:36 We'll just send the results in question document back to the client. 16:56 The next route is the one that deletes answers. 17:12 Mongoose documents have a remove method. 17:25 We can use the remove method on our answer. 17:30 Then in the callback, we'll save the parent question. 17:39 This will take another callback where we can send the resulting 18:16 question back to the client. 18:20 Finally let's complete the vote route. 18:31 First, let's add a line to the validator 18:34 to make everything a little more coherent and readable. 18:37 Now we're putting the vote string directly on the object. 18:51 It allows the reader to quickly understand what the value of the variable is about 18:55 when they read it in the next callback function here. 18:59 This is opposed to rec.params.dir, which probably wouldn't 19:09 help them understand it's holding the vote direction up or down. 19:14 Now let's call our instance method vote on the answer, passing in the vote string and 19:19 then a callback with a response back to the client. 19:25 And don't forget to include the next in your handler. 20:14 See how clean the instance method makes it easier to apply the vote to the answer? 20:20 Nice work. 20:25 This step completes our API. 20:26 We now have an express server that receives restful requests, 20:30 communicates with the database, and sends responses back to clients. 20:34 Great job. 20:38