Entity relationship diagram
ERD for freshie's database
The entity relationship diagram is a structural diagram that shows how the database is designed. The boxes in the relationship depict the model and its fields, and the lines depict how they are related to another model.
To begin, we can look at the User model. We extended the AbstractUser model that Django provides, which can be seen by the arrow pointing towards the AbstractUser model. We added an extra field to the User model, which is the isPersonalTrainer field.
One to One relationship
Focusing on the different types of users, we can see two lines extending from the top left corner of the user model. Each of these lines depict the relationship between the user model and thePersonalTrainer/Client model. Take note that the lines do not have any arrow or a circle at the end as they have a One to One relationship. This means a user can only either be a PersonalTrainer/Client.
Many to One relationship
There is also a relationship between the Client model and the PersonalTrainer model. They are connected by a line with a circle at the end. This line represents the Many to One relationship. This means that a client can only have one personal trainer, but a personal trainer can have many clients.
Many to Many relationship
Lastly, there are also lines which have circles on both ends of the line. These lines signify the Many to Many relationship. To explain what this relationship is, we should look at the relationship between themealPlan and Recipe model. A meal plan is a plan that can consist of one or more recipes, therefore it would make sense that a meal plan has many recipes. On the other hand, meal plans may consist of different recipes, but it is possible that 2 meal plans share the one or two of the same recipes. In that case, a recipe will also be required to belong to many meal plans. Hence, the Many to Many relationship is use to relate the two models.
As we have gone through all the relationships in our ERD and what they signify, we feel that being able to visualise the database in such a way helps us to understand and hence effectively use the relationships between the models to obtain the data we need without needing extra steps or tables.
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