1 00:00:05,290 --> 00:00:10,070 Welcome back in this lecture we're going to talk about flask migrate. 2 00:00:10,260 --> 00:00:16,280 We just showed how to create a database and then perform crud create read up and delete using Flast 3 00:00:16,280 --> 00:00:17,530 sequel alchemy. 4 00:00:17,550 --> 00:00:23,490 Now describe how to utilize migrations when creating a model for a database table. 5 00:00:23,490 --> 00:00:28,380 You're going to sometimes need to make adjustments that model inside your python file such as adding 6 00:00:28,380 --> 00:00:29,420 a new column. 7 00:00:29,460 --> 00:00:34,410 However just updating that Python script isn't going to automatically update the database. 8 00:00:34,410 --> 00:00:39,210 So upon making these changes we need to migrate these changes in order to update the actual sequence 9 00:00:39,360 --> 00:00:40,390 database table. 10 00:00:41,640 --> 00:00:46,450 And we can do this with flask migrate which you can install with Pip install flask migrate. 11 00:00:46,450 --> 00:00:50,950 This allows us to make adjustments in our model class and then make sure they actually take effect in 12 00:00:50,950 --> 00:00:55,190 the real SQL database and there are four main commands used at the command line. 13 00:00:55,360 --> 00:01:00,400 In order to perform this migration the first thing to do in order to make sure everything works is to 14 00:01:00,400 --> 00:01:03,240 set the flask app environment variable. 15 00:01:03,250 --> 00:01:08,980 This allows Flast migrate to no attraction that PI script is your flask application and the command 16 00:01:08,980 --> 00:01:12,050 is slightly different depending on what operating system you using. 17 00:01:12,070 --> 00:01:17,410 If you on a Mac OS or Linux you're going to say export and then all caps flask underscore app is equal 18 00:01:17,410 --> 00:01:22,900 to and then the name of the python script that actually holds your flask application. 19 00:01:23,480 --> 00:01:28,420 In Windows what you needs to do is say set and then flask app is equal to my app that. 20 00:01:28,440 --> 00:01:32,760 Or again whatever your flask application happens to be called when you run these two lines. 21 00:01:32,780 --> 00:01:37,340 You need to make sure they are in the same directory as the actual Python script. 22 00:01:37,340 --> 00:01:42,080 Otherwise your command line will say you can't find the file which makes sense because you need to be 23 00:01:42,080 --> 00:01:44,530 in the same directory in order to run that command. 24 00:01:46,530 --> 00:01:50,220 If you don't set the flask up then you're going to get an error and it'll say something like could not 25 00:01:50,220 --> 00:01:51,940 locate flask application. 26 00:01:51,940 --> 00:01:54,150 Either not provide the flask at environment variable. 27 00:01:54,150 --> 00:01:59,040 So if you ever get this error make sure you perform either one of these two lines depending on your 28 00:01:59,040 --> 00:02:03,270 operating system and you can make sure to check the migrations underscore instructions. 29 00:02:03,270 --> 00:02:08,820 Text file for a full text explanation of not just these commands but all the commands we show during 30 00:02:08,820 --> 00:02:10,800 the lecture. 31 00:02:10,970 --> 00:02:15,610 Once you set your flask application where you can do as are these three following commands. 32 00:02:15,710 --> 00:02:21,520 And so we start off with flask D-B in it and that basically sets up the migrations directory. 33 00:02:21,710 --> 00:02:23,270 Then we'll say flask. 34 00:02:23,300 --> 00:02:29,960 D.B migrate dash em and whatever your messages so that sets up the migration file and once you've done 35 00:02:29,960 --> 00:02:35,210 that you can say flask DBI upgrade that actually updates the database with the migration so to break 36 00:02:35,210 --> 00:02:40,610 down these three main steps we first actually set up a directory folder for our migrations. 37 00:02:40,610 --> 00:02:46,310 Then once you've actually made a change toward database we need to set a migration file so we say Flast 38 00:02:46,310 --> 00:02:52,480 the B migrate and then the dash and flag that stands for message and then you can report back what message. 39 00:02:52,490 --> 00:02:56,800 That way you can check the history of your migrations and you can understand what you changed. 40 00:02:56,810 --> 00:03:00,890 So maybe your message could be added column to the puppy table. 41 00:03:01,220 --> 00:03:04,540 So that's the migration file to actually perform the migration. 42 00:03:04,550 --> 00:03:05,470 You say then flask. 43 00:03:05,480 --> 00:03:09,480 DBI upgrade which then goes to migration file and performs the upgrade. 44 00:03:09,680 --> 00:03:14,460 Essentially updating the table inside of your sequel database OK. 45 00:03:14,630 --> 00:03:18,770 Let's get an idea of how to perform all of this by jumping over to our text editor. 46 00:03:18,950 --> 00:03:20,960 OK here and at my text editor. 47 00:03:21,050 --> 00:03:24,300 These are the same files and folders we were working with last time. 48 00:03:24,470 --> 00:03:30,170 Well we need to start off with is actually adding the capabilities of migration to our application and 49 00:03:30,170 --> 00:03:33,410 the way we do that is just by adding a couple of lines here. 50 00:03:33,530 --> 00:03:38,330 After you've done Pip install Flast migrate or if you're using a requirements text file you should already 51 00:03:38,330 --> 00:03:39,640 have flask migrate. 52 00:03:39,830 --> 00:03:49,360 You're going to type out from flask underscore migrate import and then you're going to import this migrate. 53 00:03:49,390 --> 00:03:54,270 Remember you can just Pipp install flask migrates. 54 00:03:54,280 --> 00:03:59,460 It's going to be a capital F dash capital M there but you should already have it in your requirements 55 00:03:59,510 --> 00:04:00,550 text file. 56 00:04:00,550 --> 00:04:06,880 Once we have imported this migrate class what we can do is we can connect this application that we created 57 00:04:06,880 --> 00:04:11,890 here on line with this database from sequel alchemy and the way we do that is the following. 58 00:04:13,140 --> 00:04:14,940 We just say migrate. 59 00:04:15,000 --> 00:04:20,760 You pass in your application and then you pass in your database and this connects the application with 60 00:04:20,760 --> 00:04:25,690 the database in order to add on migration capabilities to run those terminal commands. 61 00:04:25,830 --> 00:04:27,860 And this is all we need to do so far. 62 00:04:27,910 --> 00:04:33,360 And the reason we do this is because even though we've already set up our model class here will you 63 00:04:33,360 --> 00:04:38,600 make any adjustments to this model class such as adding a new column and we run this basic thought py 64 00:04:38,610 --> 00:04:40,130 file again. 65 00:04:40,320 --> 00:04:43,810 Our data its sequel lite database that's already been created. 66 00:04:43,860 --> 00:04:49,410 So we're not going to be able to register the new migration of a new column without using Flast migrate. 67 00:04:49,410 --> 00:04:54,300 Technically there are ways to do it in a very manual fashion but it's much much easier by just using 68 00:04:54,330 --> 00:04:55,680 Flast migrate. 69 00:04:55,680 --> 00:05:00,970 So we've imported migrate from flask migrate and then we've connected the application to the database. 70 00:05:01,170 --> 00:05:06,420 So let's save this and then we're going to come down to our command line and we first need to actually 71 00:05:06,420 --> 00:05:08,340 set our flask app. 72 00:05:08,370 --> 00:05:12,960 So because I'm on a Windows computer I use set as my key word here. 73 00:05:12,990 --> 00:05:21,250 If you're on a Mac OS or Linux you're going to use export I'm on Windows so I will say set flask underscore 74 00:05:21,880 --> 00:05:28,270 at equal to and then you just need to set it equal to whatever the python script files called that's 75 00:05:28,270 --> 00:05:30,290 holding this flask application. 76 00:05:30,430 --> 00:05:36,390 In my case I've called it basic thought Pi so I'll say set my flask app equal to basic thought by the 77 00:05:36,550 --> 00:05:39,120 enter and you shouldn't see any output there. 78 00:05:39,160 --> 00:05:41,890 Remember Mac OS or Linux are going to use export. 79 00:05:41,890 --> 00:05:47,020 Once we've set that up it's time to actually initiate and set up our migrations directory essentially 80 00:05:47,020 --> 00:05:48,580 creating a folder for us. 81 00:05:48,670 --> 00:05:57,500 So I will say now flask D-B in its hit enter and then you should see a couple of lines here. 82 00:05:57,500 --> 00:06:01,310 Things like generating a bunch of files or directories and appear at the top. 83 00:06:01,310 --> 00:06:06,590 Now you should see now a migrations folder with a bunch of stuff in it that's now going to allow us 84 00:06:06,590 --> 00:06:10,900 to connect this application with the database and very easily run migrations. 85 00:06:10,970 --> 00:06:14,310 So your migrations are going to go and say that migration is directory. 86 00:06:14,630 --> 00:06:19,330 And the next step for this is to actually create a migration command. 87 00:06:19,400 --> 00:06:26,930 So we do this by saying flask D-B migrates and then technically that's all you need to run. 88 00:06:27,170 --> 00:06:32,330 But usually it's better to leave yourself a little migration message that way when you look at the history 89 00:06:32,330 --> 00:06:35,700 of your migrations you can understand what you did for each one. 90 00:06:35,710 --> 00:06:44,130 Some subjoin say dash em and I will say created puppy table and used double quotes there. 91 00:06:44,150 --> 00:06:47,880 Hit enter and that creates a migration file. 92 00:06:47,900 --> 00:06:55,000 Now that migration has actually been executed so all we have there is a migration with a unique ID. 93 00:06:55,250 --> 00:06:58,520 And then what we need to do is actually run the migration. 94 00:06:58,520 --> 00:07:03,920 So this is very analogous to using GET AS and get commit and then get push. 95 00:07:03,920 --> 00:07:07,310 So if you're familiar get maybe this feels a little familiar to you. 96 00:07:07,490 --> 00:07:09,140 If not no worries. 97 00:07:09,350 --> 00:07:15,970 We're just going to now say flask D-B and then upgrade hit enter. 98 00:07:16,180 --> 00:07:20,310 And this will now upgrade and perform the migration for us. 99 00:07:20,370 --> 00:07:27,610 OK so now that we've performed the migration we've seen the changes in the stop basic postscript to 100 00:07:27,610 --> 00:07:33,100 our actual sequel light database so to show you a more realistic example we're going to do is add a 101 00:07:33,100 --> 00:07:34,480 column to her model. 102 00:07:34,480 --> 00:07:42,140 So let's go here to puppie the B model and then we have an ID column a name column and an age column. 103 00:07:42,280 --> 00:07:50,840 I'm now going to add a breed column say breed is equal to D-B column and this will just be text D-B 104 00:07:50,860 --> 00:07:52,240 text. 105 00:07:52,240 --> 00:07:57,880 So I've added a column to my model and I can do that here by taking name age. 106 00:07:57,880 --> 00:08:05,520 Also take brede and say self-taught breed is equal to breed. 107 00:08:05,560 --> 00:08:11,440 Now that I have updated my Python script model with this new column I should create a migration and 108 00:08:11,440 --> 00:08:14,250 then upgrade that database to effect the change. 109 00:08:14,290 --> 00:08:23,090 So the way this works is will say flask D.B migrate dash em and then give yourself a message that you 110 00:08:23,090 --> 00:08:25,540 understood what changes you did in our case. 111 00:08:25,560 --> 00:08:33,660 I'll say something like added Breede column create that migration file so that migration file is now 112 00:08:33,720 --> 00:08:38,730 underneath your migrations directory and then to actually upgrade the database to effect the changes. 113 00:08:38,730 --> 00:08:40,180 I just say flask. 114 00:08:40,430 --> 00:08:44,900 DBI upgrade and that's successfully upgraded the database. 115 00:08:44,910 --> 00:08:49,430 So now it matches up with the model I created here in my Python script. 116 00:08:49,700 --> 00:08:50,290 OK. 117 00:08:50,430 --> 00:08:56,340 That's really the basics of using Flast migrate in order to keep your actual sequel light database connected 118 00:08:56,400 --> 00:09:02,120 and updated to your model or models that play file or your application file. 119 00:09:02,160 --> 00:09:08,040 Coming up next we're going to continue our discussion of databases including relationships between two 120 00:09:08,040 --> 00:09:08,880 models. 121 00:09:08,940 --> 00:09:10,070 We'll see you at the next lecture.