1 00:00:08,120 --> 00:00:13,450 Hey everybody this is Caleb with Dev slopes and in this video we're going to be talking about core data. 2 00:00:13,490 --> 00:00:17,870 Obviously it's the most important part of this section but we're going to be talking about what even 3 00:00:17,870 --> 00:00:23,550 is core data and how does it work so that when we use it we understand what's going on behind the scenes. 4 00:00:23,570 --> 00:00:29,870 So to begin I just want to show you this graphic that I've built for us to help explain the concept 5 00:00:29,870 --> 00:00:31,880 of the core data stack. 6 00:00:31,900 --> 00:00:39,110 Ok so what you need to know is that the core data stack contains three main objects the managed object 7 00:00:39,110 --> 00:00:44,930 model the managed object context and the persistent store coordinator. 8 00:00:44,930 --> 00:00:49,970 Now if you know anything about core data already you know that its purpose is for persistence storage 9 00:00:50,240 --> 00:00:55,670 we can store things with core data and then access them later without them being destroyed every time 10 00:00:55,670 --> 00:01:02,630 that our app is closed or quit or if our phone restarts the core data allows us to persistently store 11 00:01:02,630 --> 00:01:02,920 data. 12 00:01:02,920 --> 00:01:06,160 It's really really cool now to begin. 13 00:01:06,320 --> 00:01:10,250 Every core data app has a managed object model. 14 00:01:10,360 --> 00:01:10,930 OK. 15 00:01:11,240 --> 00:01:17,600 Now what the Met managed object model does is it pulls our data model into the core data stack. 16 00:01:17,600 --> 00:01:21,920 So it basically takes our data model and pulls it into the core data stack. 17 00:01:21,920 --> 00:01:26,260 Now the managed object context is what's going to do all of the work. 18 00:01:26,270 --> 00:01:30,930 And as a developer you're actually going to be interacting with this most of the time. 19 00:01:31,080 --> 00:01:31,530 OK. 20 00:01:31,730 --> 00:01:36,630 And when you use core data in general you're going to be dealing with the managed object context. 21 00:01:36,750 --> 00:01:43,190 OK now something you need to know is that the managed object contex keeps a reference to the persistent 22 00:01:43,190 --> 00:01:46,740 store coordinator and I'm going to explain why that's important in a moment. 23 00:01:46,820 --> 00:01:53,480 But as you would expect the persistent store coordinator coordinates the persistent storage of data 24 00:01:53,490 --> 00:02:01,010 in our app K and it basically holds a persistent store that has all of our information that we save 25 00:02:01,010 --> 00:02:03,430 and want to retrieve later on. 26 00:02:03,440 --> 00:02:10,440 Now what this does is it understands our data model and it manages storing that information persistently. 27 00:02:10,600 --> 00:02:11,150 OK. 28 00:02:11,480 --> 00:02:12,680 Very very cool. 29 00:02:12,800 --> 00:02:20,210 Now to create a core data stack what we first need to do is to instantiate the data model which is used 30 00:02:20,210 --> 00:02:23,830 to create a managed object model in our core data stack. 31 00:02:23,950 --> 00:02:24,790 OK. 32 00:02:25,040 --> 00:02:31,560 Now the managed object model is required to instantiate the persistent store coordinator. 33 00:02:31,760 --> 00:02:32,480 OK. 34 00:02:32,780 --> 00:02:38,210 Now the persistent store coordinator first needs to understand the data model. 35 00:02:38,210 --> 00:02:40,190 That's why this comes second. 36 00:02:40,190 --> 00:02:45,770 The object model is created first and then because that's created the persistent store coordinator can 37 00:02:45,770 --> 00:02:46,660 be created. 38 00:02:46,730 --> 00:02:52,130 It needs to understand the model and make sure that our persistent storage is compatible with it. 39 00:02:52,340 --> 00:02:58,320 If our if our object or if our managed object model were to change and suddenly be incompatible with 40 00:02:58,320 --> 00:03:03,970 the persistent store it needs to know that that won't work and then throw the proper error. 41 00:03:04,010 --> 00:03:04,590 OK. 42 00:03:04,940 --> 00:03:11,030 Now what happens is the persistent store coordinator creates a persistent store once it knows that it's 43 00:03:11,030 --> 00:03:11,860 compatible. 44 00:03:12,140 --> 00:03:16,730 And that's why it needs to reference the managed object model because it's kind of a way to verify and 45 00:03:16,790 --> 00:03:21,710 I'm sure you're noticing that there are kind of steps and prerequisites in order to get up to the top 46 00:03:21,710 --> 00:03:23,910 of the core data stack where we interact with it. 47 00:03:24,110 --> 00:03:29,190 And this is for safety and also just to make sure that everything works as smoothly as possible. 48 00:03:29,210 --> 00:03:33,520 Now our application works with the managed object context. 49 00:03:33,640 --> 00:03:34,200 OK. 50 00:03:34,460 --> 00:03:39,860 And it's basically going to access the managed object context and the main subject context is sort of 51 00:03:39,860 --> 00:03:45,640 like the brain of core data because it manages our collection of managed objects. 52 00:03:45,690 --> 00:03:46,430 OK. 53 00:03:46,520 --> 00:03:52,700 If the managed object context needs to load data from persistent storage where all of our data is saved 54 00:03:53,390 --> 00:03:59,120 basically it asks the persistent store coordinator for it and then the well I'll draw a little arrow 55 00:03:59,120 --> 00:04:04,970 here the managed object context ask the persistent store coordinator if the persistent store is compatible 56 00:04:04,970 --> 00:04:09,980 with our data model it will return the data that we are asking for which is really neat if it needs 57 00:04:09,980 --> 00:04:13,450 to save data like let's say that our app changes some data. 58 00:04:13,640 --> 00:04:19,190 The managed object context will pass that into the persistent storage coordinator and then that tells 59 00:04:19,190 --> 00:04:24,650 the persistent store to change and to be modified then it stores it persistently and we can access it 60 00:04:24,680 --> 00:04:26,850 or save to it as much as we want. 61 00:04:26,870 --> 00:04:28,450 It's really really cool. 62 00:04:28,460 --> 00:04:35,300 So as you can see all of this is just a big ladder sort of and there are prerequisites in order to instantiate 63 00:04:35,480 --> 00:04:42,500 each of these elements so we create a data model which is pulled into the managed object model k then 64 00:04:42,800 --> 00:04:48,440 that is used to instantiate the persistent store coordinator which then checks to make sure that the 65 00:04:48,440 --> 00:04:51,190 persistent store is compatible with our data model. 66 00:04:51,440 --> 00:04:57,830 If it is then the managed object context can pull that data and displayed in our app if we want to save 67 00:04:57,830 --> 00:05:03,860 data we can push that back down through the managed object context and then into the persistent store. 68 00:05:03,860 --> 00:05:10,100 This is how core data works as kind of a Barela kind of an overview of how it works and of course as 69 00:05:10,100 --> 00:05:15,380 always with any of these topics you can always dive in deeper research deeper and find out so much more 70 00:05:15,380 --> 00:05:17,830 about how this amazing technology works. 71 00:05:17,840 --> 00:05:21,020 Apple has done an incredible job giving us core data. 72 00:05:21,170 --> 00:05:27,770 And so I'm really excited to teach you how this works and how we can basically use all of these to build 73 00:05:27,770 --> 00:05:28,280 an amazing 74 00:05:31,240 --> 00:05:36,460 So let's go ahead and let's move on to the next video where we're actually going to create our first 75 00:05:36,460 --> 00:05:40,940 Chordata data entity and create some core data attributes as well. 76 00:05:40,960 --> 00:05:45,340 We're going to talk about the core data model and how we can use it as a developer in X code. 77 00:05:45,340 --> 00:05:48,690 So let's head on over to that video and let's build that now.