WEBVTT 00:00.110 --> 00:00.500 Okay guys. 00:00.500 --> 00:06.590 So next up we are starting with another let's call it abstract concepts. 00:06.590 --> 00:11.840 So we are still not really building a full fledged blog application. 00:11.840 --> 00:18.650 I'm gonna first introduce a design pattern that's called dependency injection container. 00:18.680 --> 00:27.080 Now whatever programming language you will be using in the future, you will most likely have to work 00:27.080 --> 00:30.290 with some kind of a dependency injection containers. 00:30.290 --> 00:37.310 So I think it's super relevant and it's just important to understand this concept. 00:37.310 --> 00:39.140 So let me quickly explain this. 00:39.140 --> 00:44.000 And after that we're gonna implement a simple Di container. 00:44.150 --> 00:48.020 So dependency injection is a design pattern. 00:48.020 --> 00:56.000 And in this design pattern objects receive their dependencies instead of creating them or fetching them 00:56.000 --> 00:57.050 themselves. 00:57.050 --> 01:00.140 What does it mean in a simpler language. 01:00.380 --> 01:03.620 So let's consider that example that we have right here. 01:03.620 --> 01:05.720 You've got a database class. 01:05.750 --> 01:07.700 It needs to have a config. 01:07.700 --> 01:15.170 So it needs to get the configuration of the database the database name ports whatever information you 01:15.170 --> 01:23.120 might need about the database instead of the database class trying to fetch this information from a 01:23.120 --> 01:27.980 file, this info is just passed to the database. 01:27.980 --> 01:31.700 Typically it's just done through a constructor. 01:31.850 --> 01:36.830 And then there is another class that is called container. 01:36.860 --> 01:40.130 Or it might just be called application. 01:40.130 --> 01:47.690 This is how it would be called in our case an app that is a dependency injection container. 01:49.910 --> 01:57.140 That basically has a map of all those classes that are already created with all their dependencies. 01:57.140 --> 02:05.940 And if you have, let's say a script command line interface script that needs to load the database schema. 02:05.970 --> 02:09.540 That's something we have done previously in the previous project. 02:09.570 --> 02:10.860 Now we will have. 02:11.100 --> 02:18.150 Now we'd like to have a more generic approach to those CLI scripts and will have more of them as well. 02:18.270 --> 02:27.990 And consider we need a database so we don't want to worry about how do we get the database. 02:27.990 --> 02:33.240 Where do we get the configuration for the database from instead? 02:33.300 --> 02:42.420 All we do is we tell the Di container that we need a database, and the container already has the database 02:42.450 --> 02:47.670 object created with the proper configuration passed to it. 02:47.670 --> 02:50.010 So we just get it right away. 02:50.760 --> 02:52.680 And that's the whole concept. 02:52.710 --> 03:03.410 You simplify your own life by instantiating some of the classes within this dependency injection container, 03:03.410 --> 03:07.490 passing all the dependencies that classes need into them. 03:07.490 --> 03:14.750 Whether this is a config that's an array or some objects, whatever is needed, and then you just get 03:14.750 --> 03:18.680 things you need from this Di container. 03:20.120 --> 03:25.160 So to summarize you just reduce the coupling between components. 03:25.400 --> 03:33.020 So nothing is really tightly coupled because everything is orchestrated by this Di container. 03:33.380 --> 03:41.180 Then the code is better organized and maintainable because classes are smaller and they only do a one 03:41.180 --> 03:42.440 specific thing. 03:42.680 --> 03:47.120 And the code is also better for testability. 03:47.120 --> 03:55.550 So if you need to write any kind of automatic tests, it's easier to create them if the code is separated 03:55.550 --> 03:56.930 this way. 03:57.350 --> 03:58.160 Okay. 03:58.220 --> 04:04.490 So without any more further ado, let's just get started and do those two things. 04:04.490 --> 04:07.790 We want to have a centralized configuration. 04:07.790 --> 04:11.390 And also we want to have this Da container. 04:11.390 --> 04:18.470 And we will only create a let's call it boilerplate of this database class, because that's a topic 04:18.470 --> 04:25.670 for some next videos to actually implement some basic database abstraction that will help us with the 04:25.670 --> 04:28.760 typical tasks that we do with a database. 04:28.790 --> 04:30.260 Let's get started. 04:31.250 --> 04:37.070 So we're going to create this dependency injection container inside the car folder. 04:37.700 --> 04:39.320 Let's call it app. 04:40.130 --> 04:45.440 That's essentially a central repository of things in our app. 04:45.440 --> 04:47.000 We can call it this way. 04:47.660 --> 04:51.110 So the namespace here is core. 04:51.140 --> 04:53.060 Well that's everything just core. 04:53.060 --> 04:56.600 And the class will be called app. 04:56.600 --> 05:02.470 Now Let's define the field inside which we're going to keep all the entries. 05:02.470 --> 05:05.650 And that's just an associative array. 05:06.250 --> 05:07.810 Let's call it container. 05:07.840 --> 05:10.480 Initialize it with an empty array. 05:10.510 --> 05:12.640 This doesn't have any constructor. 05:12.640 --> 05:18.100 But we need a way to bind something to this container. 05:18.220 --> 05:25.150 So if I want to create a database class I need to put it under a specific key. 05:25.180 --> 05:36.190 That's why we need the static function that will be called bind with a key and value. 05:36.220 --> 05:37.330 That can be anything. 05:37.330 --> 05:40.720 That's why we're going to use mixed type for it. 05:42.940 --> 05:46.180 And it's void doesn't return anything. 05:47.260 --> 05:50.320 And we're just going to do static container. 05:50.320 --> 05:55.720 This is how we can refer to static data or static methods. 05:56.140 --> 06:00.180 And just under a given key, we're going to put a value. 06:00.450 --> 06:06.870 So you might also say that that's a simple wrapper around an array. 06:07.200 --> 06:16.020 But also then we need a way to get some specific entry from this container using a key. 06:17.280 --> 06:21.090 And the value can be mixed can be different things. 06:22.920 --> 06:34.080 So it's important to check if an entry exists because if the array key exists, would return false for 06:34.080 --> 06:41.370 the given key inside the static container, which is our array. 06:42.030 --> 06:44.760 Just gonna throw an exception. 06:49.560 --> 06:54.210 And then we can say that no key. 06:57.290 --> 07:00.230 Is bound in the container. 07:02.840 --> 07:04.880 So that's also a good practice to add. 07:04.910 --> 07:09.560 Use statements for exceptions even though they are globally available. 07:10.040 --> 07:14.000 So in other cases where we can find the key we just return it. 07:14.000 --> 07:20.780 This would be static container with a given key. 07:20.810 --> 07:25.670 Now this implementation of a dependency injection container might look simple. 07:25.670 --> 07:26.930 And it is simple. 07:26.930 --> 07:34.490 But generally the concept of a dependency injection container can be vastly expanded and can have some 07:34.490 --> 07:36.230 other features that will help you. 07:36.230 --> 07:36.680 Like. 07:36.680 --> 07:43.370 For example, in Symfony framework, dependency injection container has a feature called Autowiring 07:43.370 --> 07:50.360 where classes are instantiated automatically and also all their dependencies are created and automatically 07:50.360 --> 07:51.140 parsed. 07:51.170 --> 07:54.740 This is super handy with bigger applications. 07:54.770 --> 07:57.940 Okay, let's get back to our thing. 07:58.090 --> 07:58.540 Okay. 07:58.570 --> 08:01.300 At this point, we can close this container file. 08:01.300 --> 08:05.710 And I think that this video is all about organizing our app. 08:05.740 --> 08:09.040 That's why I think we need two more files. 08:09.040 --> 08:17.500 So previously we have created a bootstrap PHP file which of which was kind of initializing the whole 08:17.500 --> 08:18.250 project. 08:18.250 --> 08:20.380 And now we need this as well. 08:20.380 --> 08:27.310 So we can initialize all the command line scripts and also the server the same way. 08:27.340 --> 08:31.420 And another file that we need is config php. 08:31.660 --> 08:37.060 That would be the file that will store all of our app configuration. 08:38.620 --> 08:43.000 So the config for an app of this size can just be an array. 08:43.030 --> 08:47.380 Now I'm returning something from a file which is not a function. 08:47.380 --> 08:48.940 There is no function here. 08:48.940 --> 08:55.600 So later on you're going to see how can we require this config file and get whatever was returned from 08:55.600 --> 08:56.400 this file. 08:56.400 --> 08:59.040 So we are returning the whole app config. 08:59.040 --> 09:01.740 It's going to have two categories the app. 09:01.740 --> 09:05.280 And maybe another one can be database. 09:06.390 --> 09:10.290 So having one simple config array is enough. 09:11.820 --> 09:14.430 So let me add the app title. 09:14.790 --> 09:16.290 That's my blog. 09:16.290 --> 09:20.670 Whether we are in debug mode, let it be true for now. 09:20.700 --> 09:30.630 The driver, let's say we are using SQLite and the path does a path to a file and this would be the 09:30.630 --> 09:35.130 current directory plus the database folder. 09:35.340 --> 09:37.770 Blog SQLite. 09:38.010 --> 09:44.340 Now at this point you should create this database folder inside the root directory. 09:44.370 --> 09:47.340 This is where we're going to keep the database. 09:48.630 --> 09:55.380 So now we need to move some things from the index file into the bootstrap file. 09:55.380 --> 10:02.040 First, let me just copy everything into the bootstrap file and let's remove things that we don't need 10:02.040 --> 10:02.700 in here. 10:02.700 --> 10:11.580 So we definitely don't need routing because this is an index specific thing. 10:11.580 --> 10:19.710 Because index.php file is a so-called front controller, the bootstrap file instead needs to generically 10:19.740 --> 10:21.690 initialize the app. 10:21.900 --> 10:33.090 So for example it should have the config and config we're going to get by doing require ones using current 10:33.120 --> 10:39.150 directory and using the config php file. 10:39.150 --> 10:40.980 So notice how. 10:41.010 --> 10:48.960 So notice how I am requiring the contents of this file into the variable, which should now contain 10:48.960 --> 10:52.200 this array that is inside this config file. 10:52.500 --> 10:52.920 Okay. 10:52.950 --> 10:57.230 So we've got the config and autoloading configured. 10:57.260 --> 11:08.750 Now inside this file we should instead remove this require once and instead require once. 11:11.690 --> 11:13.070 The bootstrap file. 11:13.940 --> 11:19.280 So we need to go up and select the bootstrap file. 11:19.280 --> 11:24.830 So now all the app initialization code is in one place is in a bootstrap file. 11:24.830 --> 11:27.650 Same thing we did in the previous project. 11:27.650 --> 11:33.230 So now we can reuse this bootstrap for command line scripts. 11:34.310 --> 11:36.440 Now at this point I should be able to. 11:36.470 --> 11:41.240 VAR dump config and I should see an array. 11:42.530 --> 11:47.240 So I've got 500 error which means there is a bug to fix. 11:47.270 --> 11:56.260 So in this bootstrap file I need to remove this two dots because we no longer need to go up, as the 11:56.260 --> 11:59.680 vendor folder is at the same level as the bootstrap file. 12:00.280 --> 12:03.640 After saving the changes, this should be fine. 12:03.670 --> 12:11.170 And now we've got this whole config array on the screen, which means nothing else than we were just 12:11.170 --> 12:13.060 successful in loading it. 12:14.050 --> 12:16.960 Okay guys, so I'd like us to take a short break at this point. 12:16.960 --> 12:23.860 And next up, I'd like us to create a database class that will be a database abstraction. 12:23.860 --> 12:31.150 And then we're going to wire everything together using our dependency injection container so that we're 12:31.150 --> 12:34.390 gonna have a config inside database inside. 12:34.390 --> 12:41.650 And then if you would need to access the database, you're gonna always do it through dependency injection 12:41.650 --> 12:44.080 container that we've just created. 12:44.080 --> 12:51.430 That way, all the features that our application offers would be easily accessible everywhere. 12:51.430 --> 12:53.770 But that's for the next video.