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Welcome back, everyone, to this lecture on models and databases.

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Jingle models are defined inside a jingle app or project inside the model's top pie file, which is

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a file we haven't actually played around with yet.

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The model's class operates on a system which ends up directly converting the Python based code into

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SQL commands that interact with that database.

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This makes it much easier to work with the backend database because you just need to worry about writing

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Python code.

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Now, creating a single model is similar, it's creating a new table in a database.

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For example, you can have your database, it's an SQL light.

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And then you want to create tables that exist within that database.

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For example, let's say we're running a website for a grocery store.

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So we have customers or food items or employees.

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Later on, we'll also discuss how we can create relationships between these tables.

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For example, check if a customer actually bought a particular food item, and then we could make a

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new table for something like orders and actually connect a customer to a food item using relationships

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one to one one too many and so on.

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We'll talk about that more details later on.

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For right now, though, each database table has a name and then columns where each column will have

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a specific data type.

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For example, character strings would be that good data type for names of customers or integers.

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Would it be a good data type for ages of customers in years?

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So now let's explore how general models works in conjunction with these sort of structures.

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So inside of your models, that profile, you're going to have an import line that says something like

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from Django, that DB import models and then to create a new model which directly correlates to a new

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table in your database, you create a class and then you get to decide what you want to call that particular

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model or database.

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And then you add in attributes which end up being fields in your model.

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The attributes are analogous to columns in the table.

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This, in turn, gets automatically converted to some sort of sequel command to the database to actually

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create the table so we can see here.

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This is direct conversion from your Python code and then this gets turned into SQL code that can then

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interact with the database.

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Again, you don't need to worry about that bottom.

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You just need to worry about the Python code on top, which is much easier to work with.

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Now, let's talk about a couple of key concepts for jingle models.

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The first one is that it inherits from the built in models class.

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So there's a bunch of methods that are available to you right off the bat from inheriting from models

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that models class.

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It also uses fields to define both data types, and sometimes some data constraints don't get a little

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too confused on this because there are actual constraints classes within Django.

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But you can think of the arguments for passing into the fields as also defining constraints.

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For example, maybe you want to have a particular data type column or field require information like

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a user's email address, in which case you can add a not null constraint, not know what would be the

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terminology used in sequel.

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But later on, you'll see that there's actually easy to use arguments you can pass in during the field

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creation to put a constraint on it.

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For example, if we look back here, the first name and the last name, we're constrained to have a

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max length of 30 characters, and we can see here a character field was chosen for that particular attribute.

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Another example could be maybe you want to require unique entries, like having a unique user email

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so you don't have duplicate accounts, so you could add that on a face unique constraint.

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Again, that unique constraint is more of a sequel syntax.

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Instead, in Python, you would just say something like unique is equal to true, and we'll explore

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examples of this later on.

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So again, you end up choosing a field and then you can choose some sort of parameters or constraints

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that have something to do with that field.

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So we have the data type where the fields are chosen.

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Here we can see a character field, which is typically a string field.

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And then here we can see a max like a 30, which is just a constraint.

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This first thing can only have up to 30 characters.

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Again, it's up to you how long you want to make this sort of maxlength constraints.

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And we can check out the documentation for a list of all possible fields.

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And then within those fields, it gives you a list of all the possible arguments you can pass in.

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Jingle models can then also be later on connected through keys.

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So here we actually see two models a K two tables in the database being connected.

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The first model is a musician class model.

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And here we can see the musician has a first name, a last name and an instrument.

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They're all character fields.

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Now we can see they have a length constraint.

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Later on, we also have a class album model.

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And there we have an artist.

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But notice the artist has to be connected later on to a musician.

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So that is a direct relationship between the album and the musician.

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We can also see that the album has a name, a release date, a number of stars.

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So now we're seeing things like a character field, a deep field for dates and integer field for numbers

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that is integers and so on.

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So let's continue our discussion by exploring how to actually create a model and add fields to it.

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Later on in feature sections will actually be able to drastically advance our tango abilities by automatically

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creating templates simply by connecting them to a model that's known as class based views.

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And it's going to be super powerful tool once we understand how to use models.

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OK, I'll see you at the next lecture.