Defining the schema

Starting a project involving Protobuf always starts by defining the schema. This is known as Schema-Driven Development (SDD). We essentially define the contract that needs to be fulfilled.

We are going to take a bottom-up approach to design this schema. We are going to start by defining what a Person contact looks like. As we saw in the description of the project, a person can have an email and multiple phone numbers. This looks like the following (proto/addressbook.proto):

message Person {
  //...
  string email = 1;
  repeated PhoneNumber phones = 2;
}

While the email is simply a string, the phone number will be represented by a nested message. This is because we want to be able to store the phone number and the type of phone number it is. As we know, the type of phone number can be mobile, work, or home. This means that we can represent this set of values with an enum. Knowing all of this, we now have the following:

message...