1 00:00:08,050 --> 00:00:13,390 Hey everybody this is Caleb with Dev slopes and in this video we're gonna be talking about core data. 2 00:00:13,420 --> 00:00:17,800 Obviously it's the most important part of this section but we're going to be talking about what even 3 00:00:17,800 --> 00:00:22,630 is core data and how does it work so that when we use that we understand what's going on behind the 4 00:00:22,630 --> 00:00:23,480 scenes. 5 00:00:23,500 --> 00:00:29,800 So to begin I just want to show you this graphic that I've built for us to help explain the concept 6 00:00:29,800 --> 00:00:31,720 of the core data stack. 7 00:00:31,840 --> 00:00:39,040 K so what you need to know is that the core data stack contains three main objects the managed object 8 00:00:39,040 --> 00:00:44,890 model the managed object context and the persistent store coordinator. 9 00:00:44,890 --> 00:00:49,900 Now if you know anything about core data already you know that its purpose is for persistence storage 10 00:00:50,200 --> 00:00:55,630 we can store things with core data and then access them later without them being destroyed every time 11 00:00:55,630 --> 00:01:02,560 that our app is closed or quit or if our phone restarts the core data allows us to persistently store 12 00:01:02,560 --> 00:01:04,230 data it's really really cool. 13 00:01:04,670 --> 00:01:10,180 Now to begin every core data app has a managed object model. 14 00:01:10,350 --> 00:01:17,460 OK now what the managed object model does is it pulls our data model into the core data stack. 15 00:01:17,560 --> 00:01:21,870 So it basically takes our data model and pulls it into the core data stack. 16 00:01:21,880 --> 00:01:26,230 Now the managed object context is what's going to do all of the work. 17 00:01:26,230 --> 00:01:30,890 And as a developer you're actually going to be interacting with this most of the time. 18 00:01:31,050 --> 00:01:31,530 OK. 19 00:01:31,690 --> 00:01:36,580 And when you use core data in general you're going to be dealing with the managed object context. 20 00:01:36,730 --> 00:01:43,120 OK now something you need to know is that the managed object context keeps a reference to the persistent 21 00:01:43,120 --> 00:01:46,730 store coordinator and I'm going to explain why that's important in a moment. 22 00:01:46,780 --> 00:01:53,440 But as you would expect the persistent store coordinator coordinates the persistent storage of data 23 00:01:53,440 --> 00:02:00,940 in our app K and it basically holds a persistent store that has all of our information that we save 24 00:02:00,970 --> 00:02:03,360 and want to retrieve later on. 25 00:02:03,370 --> 00:02:10,390 Now what this does is it understands our data model and it manages storing that information persistently. 26 00:02:10,520 --> 00:02:11,050 OK. 27 00:02:11,410 --> 00:02:12,510 Very very cool. 28 00:02:12,730 --> 00:02:20,110 Now to create a core data stack what we first need to do is to instantiate the data model which is used 29 00:02:20,170 --> 00:02:23,780 to create the managed object model in our core data stack. 30 00:02:23,900 --> 00:02:24,720 OK. 31 00:02:24,970 --> 00:02:31,670 Now the managed object model is required to instantiate the persistent store coordinator. 32 00:02:31,690 --> 00:02:32,400 OK. 33 00:02:32,710 --> 00:02:38,140 Now the persistent store coordinator first needs to understand the data model. 34 00:02:38,140 --> 00:02:40,100 That's why this comes second. 35 00:02:40,150 --> 00:02:45,730 The object model is created first and then because that's created the persistent store coordinator can 36 00:02:45,730 --> 00:02:46,610 be created. 37 00:02:46,690 --> 00:02:52,270 It needs to understand the model and make sure that our persistent storage is compatible with it. 38 00:02:52,300 --> 00:02:58,280 If our if our object or a far managed object model were to change and suddenly be incompatible with 39 00:02:58,280 --> 00:03:03,740 the persistent store it needs to know that that won't work and then throw the proper error. 40 00:03:03,940 --> 00:03:04,630 OK. 41 00:03:04,870 --> 00:03:10,960 Now what happens is the persistent store coordinator creates a persistent store once it knows that it's 42 00:03:10,960 --> 00:03:11,940 compatible. 43 00:03:12,100 --> 00:03:16,670 And that's why it needs to reference the managed object model because it's kind of a way to verify and 44 00:03:16,720 --> 00:03:21,670 I'm sure you're noticing that there are kind of steps and prerequisites in order to get up to the top 45 00:03:21,670 --> 00:03:23,990 of the core data stack where we interact with it. 46 00:03:24,070 --> 00:03:29,150 And this is for safety and also just to make sure that everything works as smoothly as possible. 47 00:03:29,170 --> 00:03:33,490 Now our application works with the managed object context. 48 00:03:33,580 --> 00:03:34,300 OK. 49 00:03:34,420 --> 00:03:40,000 And it's basically going to access the managed object context and the object context is sort of like 50 00:03:40,000 --> 00:03:45,590 the brain of core data because it manages our collection of managed objects. 51 00:03:45,630 --> 00:03:46,330 OK. 52 00:03:46,480 --> 00:03:52,630 If the managed object context needs to load data from persistent storage where all of our data is saved 53 00:03:53,320 --> 00:03:59,050 basically it asks the persistent store coordinator for it and then the well I'll draw a little arrow 54 00:03:59,050 --> 00:03:59,250 here. 55 00:03:59,260 --> 00:04:04,900 The managed object context asks the persistent store coordinator if the persistent store is compatible 56 00:04:04,900 --> 00:04:09,910 with our data model it will return the data that we are asking for which is really neat if it needs 57 00:04:09,910 --> 00:04:13,600 to save data like let's say that our app changes some data. 58 00:04:13,600 --> 00:04:19,120 The managed object context we'll pass that into the persistent storage coordinator and then that tells 59 00:04:19,120 --> 00:04:24,610 the persistent store to change and to be modified then it stores it persistently and we can access it 60 00:04:24,640 --> 00:04:26,790 or save to it as much as we want. 61 00:04:26,800 --> 00:04:28,390 It's really really cool. 62 00:04:28,390 --> 00:04:35,260 So as you can see all of this is just a big ladder sort of and there are prerequisites in order to instantiate 63 00:04:35,410 --> 00:04:42,460 each of these elements so we create a data model which is pulled into the managed object model k then 64 00:04:42,760 --> 00:04:48,370 that is used to instantiate the persistent store coordinator which then checks to make sure that the 65 00:04:48,370 --> 00:04:51,370 persistent store is compatible with our data model. 66 00:04:51,370 --> 00:04:57,760 If it is then the managed object context can pull that data and displayed in our app if we want to save 67 00:04:57,760 --> 00:05:03,710 data we can push that back down through the managed object context and then into the persistent store. 68 00:05:03,820 --> 00:05:09,420 This is how core data works as kind of a an umbrella kind of an overview of how it works and of course 69 00:05:09,840 --> 00:05:15,090 as always with any of these topics you can always dive in deeper research deeper and find out so much 70 00:05:15,090 --> 00:05:17,780 more about how this amazing technology works. 71 00:05:17,790 --> 00:05:21,090 Apple has done an incredible job giving us core data. 72 00:05:21,120 --> 00:05:27,720 And so I'm really excited to teach you how this works and how we can basically use all of these to build 73 00:05:27,720 --> 00:05:28,230 an amazing 74 00:05:31,180 --> 00:05:36,400 So let's go ahead and let's move on to the next video where we're actually going to create our first 75 00:05:36,400 --> 00:05:40,910 Chordata data entity and create some core data attributes as well. 76 00:05:40,930 --> 00:05:45,280 We're going to talk about the core data model and how we can use it as a developer in x. 77 00:05:45,280 --> 00:05:48,430 So let's head on over to that video and let's build that now.