The Data Layer

The modeling of data when interacting with the application code is as important as how that data is stored in storage. The data layer is the layer that developers will interact with most often, so creating a good interface is critical to create a productive environment.

In this chapter, we will describe how to create a software data layer that interacts with storage to abstract the specifics of storing data. We will see what Domain-Driven Design is, how to use an Object-Relational Mapping framework, and more advanced patterns, like Command Query Responsibility Segregation.

We will also talk about how to make changes to the database as the application evolves and, finally, techniques to deal with legacy databases when the structure has already been defined before our involvement.

In this chapter, we will look at the following topics:

• The Model layer
• Database migrations
• Dealing with legacy databases

Let's start by...