Establishing Entity Relationships

In low level design, it is important to define the relationships between different entities in the payment app. This helps us understand how the entities are related to each other and how they interact.

Let's consider the example of the User and PaymentMethod entities in the payment app. A user can have multiple payment methods, so we need to establish a relationship between these entities.

In the database schema, we can represent this relationship using foreign keys. The User table will have a primary key column (ID) and the PaymentMethod table will have a foreign key column (User_ID) that references the ID column in the User table.

Here's an example of the database schema representation:

User Table: +----+------------------+ | ID | Username | +----+------------------+ | 1 | john@example.com | +----+------------------+

PaymentMethod Table: +----+-----------+---------+ | ID | User_ID | Method | +----+-----------+---------+ | 1 | 1 | Credit | | 2 | 1 | Debit | +----+-----------+---------+

In the PaymentMethod table, the User_ID column references the ID column in the User table, establishing the one-to-many relationship between the User and PaymentMethod entities.

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// Establishing Entity Relationships

  // In the payment app, we have multiple entities that are related to each other. Let's define the relationships between these entities.

  // One of the relationships is between the User and PaymentMethod entities.

  // A user can have multiple payment methods, so it's a one-to-many relationship.

  // We can represent this relationship using foreign keys in the database.

  // Here's an example of how we can define the relationship in the database schema:

  // User Table

  // +----+------------------+

  // | ID |     Username     |

  // +----+------------------+

  // | 1  | john@example.com |

  // +----+------------------+

  // PaymentMethod Table

  // +----+-----------+---------+

  // | ID | User_ID   | Method  |

  // +----+-----------+---------+

  // | 1  | 1         | Credit  |

  // | 2  | 1         | Debit   |

  // +----+-----------+---------+

  // We can see that the User_ID in the PaymentMethod table references the ID column in the User table.

  // This establishes the one-to-many relationship between the User and PaymentMethod entities.