1 00:00:05,210 --> 00:00:08,090 Welcome back, everyone, to this lecture on migrations. 2 00:00:09,430 --> 00:00:15,910 In general, migrations are going to be the act of connecting changes in your Jingle project or jingle 3 00:00:15,910 --> 00:00:18,910 application to the back end database. 4 00:00:19,060 --> 00:00:24,490 And this includes things like adding new models in an application, adding an entirely new application 5 00:00:24,490 --> 00:00:30,160 or even updating models of a new column or attribute in an application and models that profile that 6 00:00:30,160 --> 00:00:30,970 already exists. 7 00:00:31,150 --> 00:00:37,150 So you can think of this as any general changes that should be being kept track of in the database should 8 00:00:37,150 --> 00:00:41,500 eventually get migrated from Python code to the back end SQL database. 9 00:00:42,970 --> 00:00:48,130 Now, typically, you'll see these commands done through the managed pie file, so we're going to discuss 10 00:00:48,130 --> 00:00:55,330 three key based commands for managing migrations, and those are the Make Migrations Command, Migrate 11 00:00:55,330 --> 00:01:00,910 and then cycle migrate, which is kind of a specialty command that we won't use too often, but we will 12 00:01:00,910 --> 00:01:02,470 show it in this particular lecture. 13 00:01:03,040 --> 00:01:05,349 Let's actually begin with make migrations. 14 00:01:07,190 --> 00:01:11,240 When you make migrations, you're going to run it with the managed top pie file, so something like 15 00:01:11,240 --> 00:01:15,530 python, manage the pie, make migrations and the name of your application. 16 00:01:16,010 --> 00:01:22,040 What make migrations does is it creates but does not actually run the set of instructions that will 17 00:01:22,040 --> 00:01:24,290 apply changes to the database. 18 00:01:24,770 --> 00:01:30,080 So, for example, if you run Make Migrations app, that's going to have a Python file, be created 19 00:01:30,080 --> 00:01:33,230 and ready to be run in order to actually change that database. 20 00:01:33,560 --> 00:01:39,620 Make migrations by itself does not actually perform any changes on the database, and you should note 21 00:01:39,620 --> 00:01:45,440 that the default applications in Django, like admin or authentication, you can think of them as already 22 00:01:45,440 --> 00:01:50,240 having had their skill make migrations code ready to go, and it's already been run. 23 00:01:50,480 --> 00:01:55,910 However, they haven't actually been migrated yet, so the migrations are ready to go, but they haven't 24 00:01:55,910 --> 00:02:01,340 been applied to the database, which is why you'll be able to see most tutorials as well as our own 25 00:02:01,340 --> 00:02:01,670 code. 26 00:02:01,970 --> 00:02:03,430 Well, we run right off the bat. 27 00:02:03,440 --> 00:02:08,600 Something like Python managed that pie migrate and you saw that some migrations were being applied. 28 00:02:08,840 --> 00:02:10,070 Those were the default ones. 29 00:02:10,070 --> 00:02:11,180 But more on that later. 30 00:02:11,600 --> 00:02:17,330 When you actually run, make migrations with your app, you can actually see the migration files being 31 00:02:17,330 --> 00:02:17,750 created. 32 00:02:18,170 --> 00:02:22,970 Those will be automatically located in your application and a new directory called migrations. 33 00:02:22,970 --> 00:02:25,250 And then your very first one would be something like this. 34 00:02:25,580 --> 00:02:31,550 Zero zero one underscore initial that pie and we'll explore this python file, but it contains a set 35 00:02:31,550 --> 00:02:35,270 of instructions to go then and update your database. 36 00:02:35,270 --> 00:02:40,430 And eventually these instructions are converted into sequel that can interact with a skill based database. 37 00:02:40,910 --> 00:02:45,470 What's really nice about this is technically this Python file is very human, readable, and you can 38 00:02:45,470 --> 00:02:46,430 edit it yourself. 39 00:02:46,880 --> 00:02:48,290 Typically, we won't be doing that. 40 00:02:48,320 --> 00:02:49,670 That's pretty advanced stuff. 41 00:02:49,670 --> 00:02:53,660 And in general, you want to Django handle the heavy lifting and more complex tasks. 42 00:02:53,960 --> 00:02:56,330 But in case you wanted to know, you could go in there. 43 00:02:56,360 --> 00:02:56,930 Open it up. 44 00:02:56,930 --> 00:03:03,950 Explore and edit the sexual python file before you end up migrating or running the migrations so it 45 00:03:03,950 --> 00:03:09,500 can make migrations, makes the migration instructions, but doesn't actually run them to connect to 46 00:03:09,500 --> 00:03:10,160 the database. 47 00:03:11,190 --> 00:03:13,290 That is the migrates command. 48 00:03:13,470 --> 00:03:16,680 So we run Python, manage that pie, migrate. 49 00:03:16,830 --> 00:03:19,380 And this is going to run any existing migrations. 50 00:03:19,590 --> 00:03:20,970 How does it find those migrations? 51 00:03:21,270 --> 00:03:25,590 Well, we already know that when we create them through the Make Migrations command, that there's a 52 00:03:25,590 --> 00:03:32,010 directory called migrations in the same way jingles able to find static or template files using directories 53 00:03:32,010 --> 00:03:33,330 like static or templates. 54 00:03:33,660 --> 00:03:40,500 It's also able to find migration instructions in the migrations directories, which is why, when you 55 00:03:40,500 --> 00:03:43,350 run make migrations, those directories are created for you. 56 00:03:43,500 --> 00:03:46,920 So that's a set of instructions that migrate then runs. 57 00:03:47,100 --> 00:03:50,970 So this is actually running those Python files under the migration directory. 58 00:03:53,070 --> 00:03:56,670 Now, the last commander I want to show you is Scott Migrates. 59 00:03:56,760 --> 00:04:00,000 And this one's a little more complicated and we won't really use it that often. 60 00:04:00,330 --> 00:04:05,760 But if you go and run in Python managed up high school migrate, then the name of your application and 61 00:04:05,760 --> 00:04:09,360 the number associated with the specific migration python file. 62 00:04:09,720 --> 00:04:13,230 This would actually show you what the school code looks like. 63 00:04:13,590 --> 00:04:17,339 Keep in mind, it doesn't actually run any migration to your database. 64 00:04:17,640 --> 00:04:24,630 It just spits out the set of SQL instructions in case you had maybe a backend SQL based developer or 65 00:04:24,630 --> 00:04:30,940 database administrator who wanted to see what SQL code was actually being run to your database. 66 00:04:30,960 --> 00:04:36,540 So it's really useful for things like debugging or interfacing with some sort of database admin. 67 00:04:39,370 --> 00:04:43,840 Now again, you should note that we're not typically going to be reviewing files created under the migration's 68 00:04:43,840 --> 00:04:48,520 directory or even be running Sequel Migrate, but we're going to be doing usually is just running, 69 00:04:48,520 --> 00:04:50,440 make migrations and then migrate. 70 00:04:50,980 --> 00:04:56,050 You can think of the very first migrate command we run as executing the default make migrations that 71 00:04:56,050 --> 00:05:00,790 was already created for you upon creating the project, which is why when you create a new project, 72 00:05:00,790 --> 00:05:06,940 you can actually run Python managed up high migrate and see things like the default authentication and 73 00:05:06,940 --> 00:05:12,640 admin applications have their migrations being connected to the database, which is also why you see 74 00:05:13,150 --> 00:05:19,390 upon running migrate the database actually being created, which is why again, we run that right off 75 00:05:19,390 --> 00:05:21,520 the bat without actually creating a new application. 76 00:05:22,640 --> 00:05:24,260 So what are the actual steps for migration? 77 00:05:24,740 --> 00:05:29,120 I would recommend that you run your initial project migrant command that's going to create that database 78 00:05:29,120 --> 00:05:34,370 for you and also make the migrations necessary for things like authentication and administration. 79 00:05:34,910 --> 00:05:39,350 Then as your project grows larger, you're going to end up creating an app and creating models associated 80 00:05:39,350 --> 00:05:39,890 with that app. 81 00:05:40,280 --> 00:05:44,480 Then you have to remember to register the app and installed apps in settings that pie. 82 00:05:44,870 --> 00:05:49,610 Having to register the app makes Django very modular, and it's very plug and play that way. 83 00:05:49,820 --> 00:05:55,160 You can go ahead and grab this application and use it in a new project simply by registering it in that 84 00:05:55,160 --> 00:05:57,020 new projects settings that pi file. 85 00:05:57,080 --> 00:06:01,130 It also makes it easy to quickly disconnect an application from an existing project. 86 00:06:01,790 --> 00:06:05,930 Once you've created the app, created the models and register the app, then you run. 87 00:06:05,930 --> 00:06:11,270 Make migrations for that new app to get a set of instructions, and then you run migrate for those new 88 00:06:11,270 --> 00:06:11,960 migrations. 89 00:06:13,200 --> 00:06:19,260 OK, so let's explore these concepts based on the patient model class created in the previous lecture. 90 00:06:19,530 --> 00:06:25,170 Recall that we've already run Python Managed Pie Migrate in order to run the migrations for the very 91 00:06:25,170 --> 00:06:30,420 first set of default migrations ready to go like authentication and administration. 92 00:06:30,690 --> 00:06:34,950 Now we're focused on the models that we ourselves have created in our new application. 93 00:06:35,480 --> 00:06:36,480 Going to head to the coding app. 94 00:06:37,820 --> 00:06:45,950 OK, here we are back inside our code editor recall that we've already ran the Python managed pie migrate 95 00:06:46,070 --> 00:06:50,840 and note that it's applying migrations, all the things that are by default included in a single project 96 00:06:50,840 --> 00:06:53,930 like administration authentication sessions, et cetera. 97 00:06:54,350 --> 00:07:00,860 So it runs all those migrations, and you can also see this kind of zero zero one sort of initial Python 98 00:07:00,860 --> 00:07:05,300 script naming scheme that are underneath directories migrations. 99 00:07:05,330 --> 00:07:11,150 Now you don't really get to see those, but if you click here, you can see there's in it that PI file. 100 00:07:11,330 --> 00:07:15,530 We're going to talk a lot more about being able to edit things default at a project level. 101 00:07:15,530 --> 00:07:19,940 When we talk about the admin panel buffer right now, just go ahead and kind of ignore that and just 102 00:07:19,940 --> 00:07:24,710 think, OK, there's some default applications that are already installed under settings that PI. 103 00:07:24,980 --> 00:07:32,360 You can confirm that if you just go to the My Site settings, that PI essentially have all these installed 104 00:07:32,360 --> 00:07:34,340 apps and we ran migrations for them. 105 00:07:34,670 --> 00:07:37,250 But what about our own models on our own apps? 106 00:07:37,400 --> 00:07:42,200 So we already have the patient model created, but we haven't actually made a set of instructions yet. 107 00:07:42,710 --> 00:07:45,680 So we're going to do here because we're going to say Python. 108 00:07:46,780 --> 00:07:54,190 Managed the pie, make migrations and then pointed to our application and our application name was office. 109 00:07:54,760 --> 00:08:00,070 Now what's going to happen is it's going to try to figure out, OK, do you have an application called 110 00:08:00,070 --> 00:08:00,550 office? 111 00:08:00,790 --> 00:08:02,680 And then what are its models, etc.? 112 00:08:02,800 --> 00:08:09,940 In order to make sure this actually works, you'll need to register the application as a configuration 113 00:08:09,940 --> 00:08:11,140 within installed apps. 114 00:08:11,530 --> 00:08:17,800 So before you run this, what you need to do is come to again settings, not pie, and check the installed 115 00:08:17,800 --> 00:08:18,320 apps. 116 00:08:18,340 --> 00:08:21,220 You'll notice our office app isn't actually there yet. 117 00:08:21,700 --> 00:08:25,090 So what we're going to do is just come to app stop pie. 118 00:08:25,120 --> 00:08:26,980 We've actually already done this one time before. 119 00:08:27,370 --> 00:08:30,910 And note that by default, it's called office config. 120 00:08:31,480 --> 00:08:33,850 So we're going to just use office config. 121 00:08:33,850 --> 00:08:37,470 If you want, you can copy it, but come back to settings, not pie. 122 00:08:39,100 --> 00:08:41,650 And then we're going to add that in, so we're going to say the following. 123 00:08:42,190 --> 00:08:48,760 You can find our new installed app under office apps and then the office config. 124 00:08:48,790 --> 00:08:50,020 Don't forget the comma here. 125 00:08:50,530 --> 00:08:54,790 So this is the way you can then register this in settings that pi that way. 126 00:08:54,790 --> 00:08:56,320 When to save those changes? 127 00:08:56,440 --> 00:09:01,910 This python managed up to make migrations, knows what you're talking about when you actually say office. 128 00:09:02,260 --> 00:09:06,370 So make sure you do this first under installed apps before you actually run this command. 129 00:09:06,970 --> 00:09:08,530 If you get an error, run the command. 130 00:09:08,530 --> 00:09:11,740 You should always be checking settings that pie to see if there's a simple fix there. 131 00:09:12,130 --> 00:09:13,210 So we're going to enter here. 132 00:09:14,210 --> 00:09:19,700 And it says, OK, I made some migrations for office, and by the way, they're located here office 133 00:09:19,700 --> 00:09:20,360 migrations. 134 00:09:20,660 --> 00:09:25,250 And here's an issue about PI and the general comment there is I created model patient. 135 00:09:25,280 --> 00:09:27,680 So even the comments are automated for us, which is really nice. 136 00:09:28,190 --> 00:09:34,400 Now, if we go to office under migrations, I can now see there's zero zero zero one underscore initialed 137 00:09:34,400 --> 00:09:34,910 that pi. 138 00:09:35,390 --> 00:09:42,590 And if you open this up, this is the Python file created by Django, which is eventually going to create 139 00:09:42,830 --> 00:09:45,890 the actual sequel code in order to interact with the database. 140 00:09:46,310 --> 00:09:50,170 Technically, you could mess around with this and edit things. 141 00:09:50,180 --> 00:09:55,850 For example, you notice that it actually uses Django DB, but this time it's using a migrations class. 142 00:09:56,240 --> 00:10:00,860 So a lot of this work has already been done for you, and Django has this migration class that automates 143 00:10:00,860 --> 00:10:01,430 all of this. 144 00:10:01,850 --> 00:10:04,620 You'll notice there's a bunch of variables that are important. 145 00:10:04,640 --> 00:10:09,920 For example, initial equals true that just tells Django, by the way, this is the first migration 146 00:10:09,920 --> 00:10:11,480 I'm going to do so initial. 147 00:10:11,480 --> 00:10:12,020 It's true. 148 00:10:12,320 --> 00:10:16,580 You can actually see that reflected in the naming schema with zero zero zero one score initialed that 149 00:10:16,580 --> 00:10:16,940 PI. 150 00:10:17,480 --> 00:10:20,410 And then it says, OK, I'm going to create this model. 151 00:10:20,420 --> 00:10:23,210 The name of the model is patient, and then here are the fields. 152 00:10:23,510 --> 00:10:29,700 And then it shows you the fields, and you'll notice by default, it actually creates a primary I.D. 153 00:10:29,780 --> 00:10:34,610 key field, which if you're familiar, if Django or excuse me, familiar of sequel, that's a way to 154 00:10:34,610 --> 00:10:37,970 identify each row as a unique ID row. 155 00:10:38,000 --> 00:10:41,420 So you don't need to worry about that yourself when you create the models up here. 156 00:10:41,540 --> 00:10:46,100 So even though you have first name, last name and age, when you actually create this, there is going 157 00:10:46,100 --> 00:10:49,100 to be an initial ID index for that table. 158 00:10:49,910 --> 00:10:55,220 Now maybe you're working with someone who works a lot with a sequel database, and they're not super 159 00:10:55,220 --> 00:10:56,000 familiar of Django. 160 00:10:56,000 --> 00:11:00,800 So they ask you, Hey, by the way, what is the actual SQL code that Django is running? 161 00:11:00,980 --> 00:11:02,180 If you wanted to check that out? 162 00:11:02,450 --> 00:11:03,330 You could do the following. 163 00:11:03,410 --> 00:11:10,580 You could say Python managed our pie and then call the sequel Migrate Command, call your application 164 00:11:10,940 --> 00:11:17,390 office and then point it to the number that you were concerned about for the actual migration file. 165 00:11:17,720 --> 00:11:20,220 For example, the first one, we have zero zero zero one. 166 00:11:20,270 --> 00:11:23,240 So it can say zero zero zero one enter. 167 00:11:24,300 --> 00:11:26,400 And this will report back to you. 168 00:11:26,760 --> 00:11:30,960 The school code that will be run again, you don't need to worry about this actually running in a school 169 00:11:30,960 --> 00:11:31,260 code. 170 00:11:31,530 --> 00:11:37,200 It's just saying, OK, when you run this Python file, that's going to automatically create this SQL 171 00:11:37,200 --> 00:11:38,190 script for you. 172 00:11:38,340 --> 00:11:44,010 So then if your SQL database admin is questioning, Hey, what's Django actually doing here? 173 00:11:44,310 --> 00:11:48,780 You would just run this for whatever number of Python file migration you're interested in. 174 00:11:49,110 --> 00:11:54,840 And then you could send that back to her or him and say, Hey, here is the SQL code that is being run. 175 00:11:55,820 --> 00:12:02,030 OK, now, as I mentioned, just setting make migrations doesn't actually make the changes to the database 176 00:12:02,030 --> 00:12:03,830 file when we're ready to do that. 177 00:12:04,070 --> 00:12:09,170 We say Python, manage the pie, migrate. 178 00:12:09,530 --> 00:12:13,610 That's going to look at all the migrations that haven't been run yet throughout all the applications, 179 00:12:13,610 --> 00:12:14,870 and then I'll go ahead and run those. 180 00:12:15,410 --> 00:12:21,160 So I hit Python, manage the pie and it says, OK, I'm looking at all the operations I need to perform. 181 00:12:21,170 --> 00:12:25,520 I'm again checking admin authentication sessions and notice. 182 00:12:25,520 --> 00:12:26,690 It's also checking office. 183 00:12:27,080 --> 00:12:30,650 Now, it's not going to rerun the migrations that it already ran for Adam and authentication. 184 00:12:30,980 --> 00:12:32,100 So then it reports back to you. 185 00:12:32,120 --> 00:12:37,340 Well, the migrations that I haven't run yet that I'm going to run are the office ones and it says I'm 186 00:12:37,340 --> 00:12:43,220 applying office zero zero one initial pilot, which is basically saying I ran this python file, which 187 00:12:43,220 --> 00:12:46,940 in turn creates this SQL code, which in turn interacts with the database. 188 00:12:47,270 --> 00:12:50,330 OK, so that's the very basics of migrations. 189 00:12:50,360 --> 00:12:55,610 Again, you have the make migrations, which creates this python file set of instructions. 190 00:12:55,940 --> 00:13:00,470 And then if you did want to check that skill code, you could say SQL migrate to check that out. 191 00:13:00,890 --> 00:13:06,390 And if you are ready to actually run the migration, then you say Python managed API migrate. 192 00:13:06,890 --> 00:13:07,730 OK, that's it. 193 00:13:08,090 --> 00:13:11,930 I'll see you in the next lecture or begin to talk about database interaction. 194 00:13:11,960 --> 00:13:17,000 How do I create, read, update and delete from this backend database through Python and Django?