Building data-driven web apps with Flask and SQLAlchemy Transcripts
Chapter: MongoDB edition
Lecture: Importing the data from SQL to Mongo

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0:00 It's looking like our app is working pretty well.
0:01 If we go and run it, try to pull up the home page here
0:05 you see, hey it looks like it's working.
0:07 It turns out when we have actual data
0:09 there's a few minor tweaks we're going to have to change.
0:11 That's not a big deal.
0:13 The bigger deal is that, well, there's no data here.
0:16 We have zero projects, zero releases, zero users.
0:20 How do we get that data in there?
0:21 We did have this load_data here where we took
0:24 a JSON file and imported into SQLAlchemy
0:27 but that's not what we're after.
0:29 What we want to do is take the data that's
0:30 in SQLAlchemy and put it in to MongoDB.
0:33 So I'm going to show you a cool technique
0:34 how you can take any database you connect
0:37 to through SQLAlchemy, go query all the data
0:40 and then transform that into MongoDB
0:42 MongoEngine classes and save that into MongoDB.
0:44 Basically, migrate data from one database type to the other.
0:48 So let's go create another script here.
0:57 So we have this file, now it's a little bit complicated
0:59 and not really worth you watching me type it in
1:01 so I'm going to paste something here
1:03 and we're going to talk through it real quick.
1:05 So we're going to go and initialize
1:07 both database connections.
1:09 One to MongoDB, as well as SQLAlchemy.
1:12 Because we need to read the data from SQLAlchemy or SQLite
1:15 and then push it into, save it into MongoDB.
1:18 And then, these three functions here, they all work
1:22 basically the same.
1:23 The first question is, are there any users?
1:25 If there are, we probably already run this
1:27 don't have to do that.
1:28 So be careful of the start with zero
1:30 but then it will not override it.
1:32 Then we just go and do a query against SQLAlchemy
1:34 for all the users. Get them all
1:37 and then we loop over them, one at a time
1:39 we create a MongoDB user, set the properties
1:42 and then call save.
1:44 Hash password is SQLAlchemy's hash password.
1:46 Name is SQLAlchemy's name. And that's it!
1:49 If you have a ton of data insert, doing a save
1:52 one at a time can be pretty slow, so you can do
1:54 bulk inserts as well with MongoEngine and what not
1:58 we don't have that much data. We're not doing it.
2:00 All the others, they're pretty much the same
2:02 packages, and releases, and so on.
2:05 So I want to show you a quick trick we're doing up here
2:07 that's kind of cool.
2:08 We're working with package, right?
2:10 So here's a package class and here's a package class
2:12 how in our code do we know which is which?
2:14 Well this one is the MonogDB one and this one
2:17 is the SQLAlchemy one.
2:18 So we're importing is as SQL package Mongo package
2:21 or SQL user and Mongo users.
2:22 That's just a cool technique to help you remain sane
2:25 while you're trying to run this.
2:27 So let's go ahead and run this and see what happens.
2:32 Takes a second, it's doing some work, and it's done!
2:39 So let's go look over here and we can do our query again.
2:42 Go show me all the packages. Ta-dah! There they are.
2:44 How cool is that?
2:46 We're got our ID name and email created.
2:48 We didn't copy over maintainers, because it turns out
2:50 we we're storing them in SQLAlchemy, so there's really
2:52 no way to copy them over.
2:54 Also, MongoEngine does not insert unmodified values.
2:58 Okay, so notice that some of the values that are not here
3:03 they're simply just not in there.
3:05 This is the package we want to move on
3:06 but still, we don't have the maintainers copied over.
3:09 Right? You can see it's just the values that we've set.
3:12 These times are the ones that come out of SQLAlchemy
3:16 not just the default ones, right?
3:18 So we copied all this over, saved in
3:20 and it's good to go.