Building data-driven web apps with Pyramid and SQLAlchemy Transcripts
Chapter: Modeling data with SQLAlchemy classes
Lecture: SQLAlchemy model base class
0:00 Now for SQLAlchemy to work right
0:02 we need to put a base class here.
0:05 It needs to be a special one.
0:06 Every class that maps to the same database
0:10 needs to use the same base class.
0:13 You can have different ones, like if you have
0:15 an analytics database, and you have a core data database
0:19 those might be different classes
0:20 but all the ones that go into one database
0:22 they should be the same.
0:24 Okay, so how do we do that?
0:25 Well, we're going to define a class
0:27 and it's really quite simple.
0:28 You sort of create one and only one of them
0:31 from SQLAlchemy.
0:33 So I'm going to put that into its own separate file, now.
0:36 I think this one totally justifies its own file.
0:39 What I'm going to do here is pushing the limit
0:41 of maybe this is a little too fine grained
0:43 but there's only one and it's supposed to be shared.
0:45 So I think what I'm going to do is, do this.
0:51 Create a model base class and then we have to
0:55 import SQLAlchemy.extensions.declarative
1:01 I'll just say, shorts we don't have to say
1:02 too much there just, as dict then I'm going to
1:04 create a class called SQLAlchemyBase.
1:09 This class is the class that's going to be the base class
1:12 but instead of defining it this way
1:13 we use a factory method out of this place here
1:17 so we say, declarative_base like that.
1:23 And that's it.
1:24 This is now our base type.
1:26 It gets created at runtime by SQLAlchemy
1:28 and then, by virtue of deriving from it, it basically means
1:33 we're telling SQLAlchemy, "Here's another class that you're managing."
1:36 So for example, put that here and let PyCharm import it.
1:42 So for the top, we have from model base, import this
1:45 and those two lines are going to pretty much be the same
1:48 for all of our types.
1:49 And that's it, this class can now be loaded and saved
1:54 from the database once we connect to it.