WEBVTT 00:00.845 --> 00:01.770 -: In the last section, 00:01.770 --> 00:04.170 we added in some logic to the express server 00:04.170 --> 00:05.820 that's going to get us a connection over 00:05.820 --> 00:07.440 to Postgres over here, 00:07.440 --> 00:09.420 and create a new table inside the database 00:09.420 --> 00:11.220 if it doesn't already exist. 00:11.220 --> 00:12.870 We're now gonna make sure that the express server 00:12.870 --> 00:14.640 has a connection over to Redis. 00:14.640 --> 00:16.410 So anytime that user submits a new number 00:16.410 --> 00:18.300 to the React Application. 00:18.300 --> 00:21.115 React App will push that index over to the express server, 00:21.115 --> 00:23.070 and the express server will then push 00:23.070 --> 00:26.555 that index into the running Redis instance. 00:26.555 --> 00:29.070 So back inside of my index dot js file, 00:29.070 --> 00:31.005 inside of the server directory. 00:31.005 --> 00:32.820 Underneath all the Postgres stuff, 00:32.820 --> 00:35.497 I'll put on a new section that we'll call, 00:35.497 --> 00:37.533 `Redis client setup. 00:39.090 --> 00:43.260 So here we'll say, const Redis is require Redis, 00:43.260 --> 00:44.970 and we're going to do some very similar, 00:44.970 --> 00:47.090 create client calls, that we did inside 00:47.090 --> 00:49.744 of the worker folder just a moment ago. 00:49.744 --> 00:52.611 We'll say, const Redis client is 00:52.611 --> 00:54.693 Redis dot create client. 00:55.620 --> 00:57.690 I'm gonna pass this an object 00:57.690 --> 01:01.599 that's gonna have a host coming from keys dot Redis host. 01:01.599 --> 01:05.280 A port from keys dot Redis port, 01:05.280 --> 01:08.283 and then finally we'll define a retry strategy. 01:09.390 --> 01:12.480 That's gonna be an arrow function that always 01:12.480 --> 01:14.550 returns the number 1000 to say 01:14.550 --> 01:16.380 if we ever lose connection to Redis 01:16.380 --> 01:19.650 try to reconnect to it once every one second. 01:19.650 --> 01:21.330 One thing I wanna point out here is that the key 01:21.330 --> 01:26.130 for retry strategy is separated by a underscore right there 01:26.130 --> 01:29.233 as opposed to the JavaScript standard of Camel case like so. 01:29.233 --> 01:32.370 So make sure that you've got underscore strategy 01:32.370 --> 01:34.653 and strategies should have a lowercase s. 01:36.543 --> 01:38.580 And then very similar to what we did before 01:38.580 --> 01:40.470 where we created a duplicate connection 01:40.470 --> 01:43.230 I'm going to also make a Redis publisher. 01:43.230 --> 01:45.930 I'm gonna use a more descriptive name this time around 01:45.930 --> 01:49.380 then when we created that duplicate copy of the Redis client 01:49.380 --> 01:51.805 over inside of the worker index dot js file. 01:51.805 --> 01:54.600 Just because we have many more variables inside 01:54.600 --> 01:56.970 of this server file. 01:56.970 --> 01:58.860 So I'll say const Redis publisher 01:58.860 --> 02:00.100 will be Redis client 02:01.590 --> 02:03.390 dot duplicate. 02:03.390 --> 02:04.290 Now in case you're curious 02:04.290 --> 02:06.270 we are making these duplicate connections 02:06.270 --> 02:08.070 in both files because according 02:08.070 --> 02:11.160 to the Redis documentation for this JavaScript library 02:11.160 --> 02:14.088 if we ever have a client that's listening 02:14.088 --> 02:16.710 or publishing information on Redis 02:16.710 --> 02:18.966 we have to make a duplicate connection 02:18.966 --> 02:20.850 because when a connection is turned 02:20.850 --> 02:22.590 into a connection that's going to listen 02:22.590 --> 02:24.630 or subscribe or publish information 02:24.630 --> 02:26.580 it cannot be used for other purposes. 02:26.580 --> 02:28.320 So that's why we're doing this duplicate thing 02:28.320 --> 02:29.523 in both locations. 02:31.380 --> 02:32.970 All right, so that's pretty much it 02:32.970 --> 02:34.470 for the initial setup here. 02:34.470 --> 02:36.210 Now we're going to start to define some 02:36.210 --> 02:38.160 of the different routes that our server is going to 02:38.160 --> 02:39.840 eventually respond to. 02:39.840 --> 02:40.740 So down here we'll put 02:40.740 --> 02:44.913 down another section and we'll say express route handlers. 02:45.990 --> 02:47.850 I'm gonna first make a test route 02:47.850 --> 02:49.140 something that we can use to make sure 02:49.140 --> 02:51.810 that our application is working the way we expect. 02:51.810 --> 02:54.753 I'll say app dot GIT forward slash. 02:56.610 --> 02:57.660 This thing is going to be called 02:57.660 --> 03:00.270 with a request and response. 03:00.270 --> 03:03.870 Anytime someone makes a request to the route route 03:03.870 --> 03:07.020 of our express application, I'm gonna send back a response 03:07.020 --> 03:07.853 of hi 03:07.853 --> 03:08.686 like so 03:11.580 --> 03:14.003 we'll then define another route handler 03:14.003 --> 03:18.423 at the route values slash all. 03:20.130 --> 03:21.720 This route handler is going to be used 03:21.720 --> 03:26.010 to query or running Postgres instance and retrieve all 03:26.010 --> 03:28.380 of the different values that have ever been submitted 03:28.380 --> 03:29.490 to Postgres. 03:29.490 --> 03:31.370 So this is essentially going to return all 03:31.370 --> 03:33.360 of the values that have ever been submitted 03:33.360 --> 03:34.193 to our application 03:34.193 --> 03:36.870 or all the indices that have been submitted. 03:36.870 --> 03:39.900 This is going to be an async arrow function 03:39.900 --> 03:42.250 so don't forget the aysync keyword right there. 03:43.440 --> 03:45.920 We'll do request and response, 03:45.920 --> 03:47.280 and then inside of here 03:47.280 --> 03:49.950 we're gonna make a query to the Postgres instance 03:49.950 --> 03:53.400 by saying Const values is a weight 03:53.400 --> 03:56.070 e.g client dot query. 03:56.070 --> 03:57.690 And the query we're going to issue is going to 03:57.690 --> 03:58.835 be a sequel query. 03:58.835 --> 04:02.943 We'll say select star from values. 04:05.910 --> 04:08.040 So essentially look at the values table 04:08.040 --> 04:09.630 that we created a little bit ago 04:09.630 --> 04:11.700 and pull all the information out of it. 04:11.700 --> 04:14.610 And then we're gonna send all that information back 04:14.610 --> 04:17.610 to whoever is making request to this route. 04:17.610 --> 04:21.660 So I'll say res dot send values dot rows. 04:21.660 --> 04:23.460 The dot rows right here is gonna make sure that 04:23.460 --> 04:26.070 we only send back the actual information that we retrieve 04:26.070 --> 04:29.520 from the database and no other information that is contained 04:29.520 --> 04:30.950 inside this values object. 04:30.950 --> 04:33.510 The other information that's in here is some information 04:33.510 --> 04:36.240 about the query itself, like say, how long it took 04:36.240 --> 04:38.760 or what tables we touched or stuff like that. 04:38.760 --> 04:41.520 So we're just gonna send back the relevant information 04:41.520 --> 04:43.920 to whoever made a request to this route handler. 04:45.418 --> 04:49.320 Next up we're gonna add another GIT Request handler 04:49.320 --> 04:52.080 to value values slash current. 04:52.080 --> 04:54.540 This is going to be another async function, 04:54.540 --> 04:56.610 so don't forget the async keyword. 04:56.610 --> 04:59.790 We'll do rack res and inside of here 04:59.790 --> 05:02.670 we're gonna reach into Redis this time. 05:02.670 --> 05:04.936 So reach into Redis and we're going to retrieve all 05:04.936 --> 05:07.710 of the different values, all the different indices 05:07.710 --> 05:10.440 and calculated values that have ever been submitted 05:10.440 --> 05:11.670 to our backend. 05:11.670 --> 05:13.140 So find all the value 05:13.140 --> 05:15.712 or all the indices that have been requested from our users 05:15.712 --> 05:18.360 and return all the accompanying values that have 05:18.360 --> 05:20.013 been calculated for each one. 05:22.290 --> 05:27.290 So inside of here I'll look at Redis client HGETALL 05:27.690 --> 05:28.890 which essentially means look 05:28.890 --> 05:31.830 at a hash value inside the Redis instance 05:31.830 --> 05:34.053 and just get all the information from it. 05:34.890 --> 05:37.773 The hash that we're gonna look at is called values. 05:39.060 --> 05:41.760 We're going to pass in a callback function that has 05:41.760 --> 05:43.270 air and values 05:45.090 --> 05:46.560 inside this thing we're just gonna 05:46.560 --> 05:49.323 send back res dot send values. 05:51.330 --> 05:53.220 Now, quick note here, you'll notice that up here 05:53.220 --> 05:56.730 we're making use of the Await or Async Await syntax 05:56.730 --> 05:59.640 and down here we're doing a very classic callback 05:59.640 --> 06:02.670 for our asynchronous route data handling. 06:02.670 --> 06:04.680 Unfortunately, the Redis library 06:04.680 --> 06:07.680 for note js doesn't have out the box promise support 06:07.680 --> 06:09.660 which is why we have to use callbacks 06:09.660 --> 06:13.140 as opposed to making use of the nice async await syntax. 06:13.140 --> 06:14.590 Just a quick side note there. 06:16.350 --> 06:18.060 All right, so I know this is a long section 06:18.060 --> 06:20.850 but we just need to do one more route handler down here. 06:20.850 --> 06:22.650 So let's just get that done with. 06:22.650 --> 06:24.570 So that last route handler that we're going to 06:24.570 --> 06:26.788 define is going to receive new values 06:26.788 --> 06:29.010 from the React application. 06:29.010 --> 06:31.380 So anytime that a user puts a new index in here 06:31.380 --> 06:33.480 like say 7, and then clicks on submit 06:33.480 --> 06:36.720 they're gonna try to post that information to our back end. 06:36.720 --> 06:39.450 So from the React application to the express server 06:39.450 --> 06:42.210 that's the route handler that we're gonna define right now. 06:42.210 --> 06:43.263 Last route handler. 06:44.730 --> 06:46.680 So I'll say app dot post 06:46.680 --> 06:47.940 because this time we're going to be listening 06:47.940 --> 06:49.593 for a post request, 06:50.670 --> 06:51.503 and I wanna watch 06:51.503 --> 06:54.363 for a post request to the values endpoint. 06:55.830 --> 06:59.223 We'll then put in an aysync callback, so rec res. 07:00.480 --> 07:01.380 And then inside of here 07:01.380 --> 07:05.070 we're gonna first get the index that the user just submitted 07:05.070 --> 07:08.973 from rec dot body dot value, excuse me, index. 07:10.050 --> 07:11.190 So look at the index 07:11.190 --> 07:15.060 that the user just submitted from rec dot body dot index. 07:15.060 --> 07:15.930 We're then gonna make sure 07:15.930 --> 07:19.650 that the index that was submitted is less than 40. 07:19.650 --> 07:21.531 So if a user puts in a number that's 07:21.531 --> 07:23.910 or an index that's really high, 07:23.910 --> 07:25.950 calculating a Fibonacci number 07:25.950 --> 07:27.750 with a method that we've put together inside 07:27.750 --> 07:29.220 of our worker process 07:29.220 --> 07:32.550 for a very large index will take a very, very 07:32.550 --> 07:33.480 very long time, like 07:33.480 --> 07:36.870 on the order of years or decades or centuries. 07:36.870 --> 07:39.621 So we're just going to arbitrarily cap the size 07:39.621 --> 07:41.454 of the index that the user submit to make sure 07:41.454 --> 07:43.762 that our worker process does not just 07:43.762 --> 07:47.343 get arbitrarily forever locked down for all time. 07:48.390 --> 07:53.390 So I'll say if our sent of index is greater than 40 07:54.238 --> 07:56.490 then we're going to immediately return 07:56.490 --> 08:00.580 and send back a status of 4 22 08:01.500 --> 08:06.500 and send the message value or index to high like so. 08:13.047 --> 08:15.570 So now that we've got this index or the number 08:15.570 --> 08:18.761 that we're going to use to calculate a Fibonacci value 08:18.761 --> 08:20.430 we're gonna first take that value 08:20.430 --> 08:23.010 and we're gonna put it into our Redis data store. 08:23.010 --> 08:26.350 So I'll say Redis client dot h set 08:27.720 --> 08:29.070 values 08:29.070 --> 08:31.110 we'll put in the index, and then 08:31.110 --> 08:35.703 as the value for that index, we're gonna put in nothing yet. 08:37.170 --> 08:40.410 So eventually the worker is gonna come to the hash or kind 08:40.410 --> 08:42.660 of data structure that we're creating inside of Redis 08:42.660 --> 08:44.640 and it's going to replace this nothing 08:44.640 --> 08:47.190 yet string with the actual calculated value. 08:47.190 --> 08:49.230 So nothing yet essentially means we've not yet 08:49.230 --> 08:52.743 calculated a Fibonacci value for this particular index. 08:54.592 --> 08:56.098 After we put the value in there 08:56.098 --> 08:58.499 we'll look at the Redis publisher 08:58.499 --> 09:02.580 and we'll publish a new insert event 09:02.580 --> 09:04.050 of that index. 09:04.050 --> 09:06.690 So this right here is gonna be the message that gets sent 09:06.690 --> 09:08.250 over to that worker process. 09:08.250 --> 09:10.080 It's gonna wake up the worker process and say, 09:10.080 --> 09:12.148 hey, it's time to pull a new value out of Redis 09:12.148 --> 09:15.870 and start calculating the Fibonacci value for it. 09:15.870 --> 09:17.160 And then after doing both those steps 09:17.160 --> 09:17.993 we're also going to look 09:17.993 --> 09:21.300 at our Postgres client and we're going to add 09:21.300 --> 09:25.153 in the new index that was just submitted. 09:25.153 --> 09:28.860 So remember, the Postgres database is going to 09:28.860 --> 09:32.310 be storing this kind of permanent record right here. 09:32.310 --> 09:33.960 It's gonna be storing the permanent record 09:33.960 --> 09:36.930 of all the different indices that have ever been submitted 09:36.930 --> 09:37.953 to our application. 09:39.270 --> 09:42.240 So we'll say pg client dot query 09:42.240 --> 09:45.750 insert into values. 09:45.750 --> 09:50.520 We are inserting a value for the number column 09:50.520 --> 09:52.037 so I'm gonna say number 09:52.037 --> 09:57.030 and then values dollar sign 1 like so. 09:57.030 --> 10:00.240 I'll then put in a comma, an array 10:00.240 --> 10:02.340 and I'll list out the index that was submitted 10:02.340 --> 10:04.023 to our application for that. 10:06.750 --> 10:09.270 So this line right here is gonna take the submitted index 10:09.270 --> 10:11.583 and permanently store it inside of Postgres. 10:13.050 --> 10:15.240 And then finally, as a response at the very end 10:15.240 --> 10:16.980 I'll say res dot send. 10:16.980 --> 10:19.410 And we'll just send back some arbitrary response 10:19.410 --> 10:21.450 like working true to say. 10:21.450 --> 10:22.283 All right 10:22.283 --> 10:24.720 we are doing some work to calculate your Fibonacci value. 10:26.820 --> 10:31.110 So now as the very last step inside of the index dot js file 10:31.110 --> 10:33.210 we're gonna set up app dot listen 10:33.210 --> 10:36.310 and we're gonna listen to port 5000 inside of here 10:37.500 --> 10:40.800 and we'll set up a callback and we'll just say something 10:40.800 --> 10:45.800 like console log listening like so. 10:47.880 --> 10:49.500 All right, so I know that's a lot of typing 10:49.500 --> 10:50.340 but that's all we have to do 10:50.340 --> 10:54.870 for the index dot js file and side of our express folder. 10:54.870 --> 10:57.330 So again, we're gonna try executing this file 10:57.330 --> 10:58.710 at the command line. 10:58.710 --> 11:00.720 Now the file's not gonna work as it stands right now 11:00.720 --> 11:02.880 because we do not have a running Redis server 11:02.880 --> 11:05.310 or a running Postgres server, but it's going 11:05.310 --> 11:06.990 to at least allow you to determine 11:06.990 --> 11:09.483 whether or not you have a typo inside this file. 11:10.701 --> 11:13.110 So I'm back inside of the complex directory 11:13.110 --> 11:15.888 which recall is the root folder for our entire project. 11:15.888 --> 11:19.440 I'm gonna change into the server directory, and then inside 11:19.440 --> 11:22.620 of here, I will run node index dot js. 11:22.620 --> 11:25.020 Now you want to see a message of something 11:25.020 --> 11:27.630 like cannot find module express. 11:27.630 --> 11:31.290 If you see anything else, that means that you have a typo 11:31.290 --> 11:34.313 somewhere either inside of the index dot js file 11:34.313 --> 11:37.200 or inside of the keys dot js file. 11:37.200 --> 11:38.910 So you'll want to look at both these files and 11:38.910 --> 11:40.620 try to find the typo. 11:40.620 --> 11:42.690 Now, if you can't find the typo, that's totally fine. 11:42.690 --> 11:45.990 Remember, I'm gonna post all of the correct code that we're 11:45.990 --> 11:48.651 writing right now in like one or two or three more videos. 11:48.651 --> 11:51.450 So if you see an issue, don't sweat it. 11:51.450 --> 11:52.950 You don't have to stare at your code all day. 11:52.950 --> 11:54.900 You can always just open up my copy 11:54.900 --> 11:57.257 of this project and copy paste everything 11:57.257 --> 12:02.257 from my index dot js file into your index dot js file. 12:02.498 --> 12:05.070 Okay, so let's take a quick pause right here 12:05.070 --> 12:06.170 and the next section, I think 12:06.170 --> 12:08.880 that we've got just like a tiny bit more. 12:08.880 --> 12:09.713 Actually, you know what? 12:09.713 --> 12:10.546 I think that might be it. 12:10.546 --> 12:11.880 Oh, we gotta do the React application. 12:11.880 --> 12:12.870 Of course. 12:12.870 --> 12:14.130 How could I forget? 12:14.130 --> 12:16.380 All right, so quick pause, come back in just a second 12:16.380 --> 12:17.970 and we'll put the React app together. 12:17.970 --> 12:19.563 So I'll see you in just a bit.