Understanding one-to-many relationships

One-to-many relationships are the most common relationships in a relational database. They are also called parent-child (children) relationships. For example, an invoice has a collection of invoice items. In this section, we will learn how to configure a one-to-many relationship in EF Core and how to implement CRUD operations for entities with a one-to-many relationship.

Let us continue to use the invoice sample application. You can find the sample code of the EfCoreRelationshipsDemo project in the chapter6 folder. If you would like to test the code following the book, you can continue to work on the BasicEfCoreDemo project. Note that the InvoiceDbContext class has been renamed SampleDbContext in the sample code.

Next, let us update the Invoice class and create an InvoiceItem class, then define the one-to-many relationship between them.

One-to-many configuration

To demonstrate a one-to-many relationship, we need to add a new class...