Getting Started with Models

Introduction

You might recall that at the beginning of this course, we learned about three components of a web application:

1. Views
2. Templates
3. Models

In previous lessons, we have covered two of these components (views and templates). In this lesson, we will figure out how to create models. Later in the course, we will also get to know how to manipulate these models.

Steps to create a User model in a database

Again, let’s get help from the example we have been using. We used a dictionary to store the user’s data.

users = {
    "archie.andrews@email.com": "football4life",
    "veronica.lodge@email.com": "fashiondiva"
}

But this is poor application logic. Therefore, to store the user data inside the database, we first need to create models. The models will define the schema for the database table, its properties, and its functionalities.

Create a model class for User

First, we will create a class for the User table. This class will inherit from the model class from SQLAlchemy.

class User(db.Model):

Add columns/attributes

Next, we will add the columns for the table. In the example, the users only had two fields: email and password. So we will add them. Each column will be an object of the Column subclass of SQLAlchemy.

    email = db.Column(db.String, primary_key=True, unique=True, nullable=False)
    password = db.Column(db.String, nullable=False)

In the snippet given above you can observe that we have given some additional parameters to the columns. The first parameter of the column defines the data type for the column. Following are the allowed class names:

1. Integer
2. String(size)
3. Text
4. DateTime
5. Float
6. Boolean
7. PickleType
8. LargeBinary

There are many optional parameters as well; some of the most commonly used ones are given below:

• primary_key: If set True, it will indicate the primary key of the table.
• nullable: If set False, it will be compulsory to set the value for that column.
• unique: If this parameter is set to True then all values for this column are checked for uniqueness.
• index: Setting it to True indicates that this column will be indexed.

Creating a table in a database

Now, with a simple command, the model that we just made will be created in the database.

db.create_all()

📌 Important Note: The create_all() command should be called after the models are declared. If the models are defined in a separate module, then they should be imported first. Furthermore, during development, if new models are created, then this command only creates the newly defined models.

Complete implementation

Let’s add this implementation to the previously discussed example.

📌 Note: You will notice that we have not yet removed the dictionary from this example. This is because we have yet to learn how to retrieve and manipulate the data from the models.