added explanation on why id is omitted

also added an explanation on why the orchestraId field must be defined in the interface, although we don't explicitly define it

express-main-example/src/sequelize/models/instrument.model.ts

@@ -5,9 +5,15 @@ interface InstrumentAttributes {
 	id: number;
 	type: string;
 	purchaseDate: Date;
+
+	// We need to specify the 'orchestraId' field here,
+	// because it will automatically be defined later on
+	// when Sequelize applies the associations
 	orchestraId: number;
 }
 
+// we can omit the 'id' field, since we aren't required
+// to set it manually when creating a new entry
 interface InstrumentCreationAttributes
 	extends Omit<InstrumentAttributes, "id"> {}
 

express-main-example/src/sequelize/models/orchestra.model.ts

@@ -6,6 +6,8 @@ interface OrchestraAttributes {
 	name: string;
 }
 
+// we can omit the 'id' field, since we aren't required
+// to set it manually when creating a new entry
 interface OrchestraCreationAttributes extends Omit<OrchestraAttributes, "id"> {}
 
 export const Orchestra: ModelDefined<

express-main-example/src/sequelize/models/user.model.ts

@@ -6,6 +6,8 @@ interface UserAttributes {
 	username: string;
 }
 
+// we can omit the 'id' field, since we aren't required
+// to set it manually when creating a new entry
 interface UserCreationAttributes extends Omit<UserAttributes, "id"> {}
 
 export const User: ModelDefined<