Creating one-to-one maps

Entities can be related to each other in different ways. A one-to-one relation is one where each individual entity may be related to another, and this other one, if it exists, is directly related to the first. Examples include the following:

• A relation from a person to their address, assuming that no two people share the same address

• Additional details for an order

• A person and their pet

• A country and its head of state

A one-to-one relation is easy to represent in domain model terms: each of the entities has a reference to the other. Only one side can be made required; otherwise, we would have a problem: which one comes first? Let's see how we can map this kind of relation in Entity Framework Core.

Getting ready

We will be using the NuGet Package Manager to install the Entity Framework Core 1 package, Microsoft.EntityFrameworkCore. We will also be using a SQL Server database to store the data, so we will also need Microsoft.EntityFrameworkCore.SqlServer.

Finally, xunit is...