Facade pattern

Definition

Provide a unified interface to a set of interfaces in a subsystem.
Facade defines a higher-level interface that makes the subsystem easier to use.

• Reorganize a system with many subsystems into identifiable layers with single entry points
• Simplify the interface to a complex subsystem

Exemple

User.cs

public class User { public string Name { get; private set; } public User(string name) { Name = name; } }

Group.cs

public class Group { public string Name { get; private set; } public ICollection<User> Users { get; private set; } public Group(string name) { Name = name; Users = new List<User>(); } }

UserService.cs

public class UserService { public User CreateUser(string userName) => new User(userName); }

GroupService.cs

public class GroupService { IDictionary<string, Group> groupsByName; public void AddUserIntoGroup(User user, Group group) { group.Users.Add(user); } public Group GetByName(string groupName) => groupsByName.TryGetValue(groupName, out var group) ? group : null; }

UserGroupFacade.cs

public class UserGroupFacade { UserService userService; GroupService groupService; public UserGroupFacade(UserService userService, GroupService groupService) { this.userService = userService; this.groupService = groupService; } public void CreateAdminUser(string userName) { var user = userService.CreateUser(userName); var adminGroup = groupService.GetByName("Admin"); groupService.AddUserIntoGroup(user, adminGroup); } }

var userService = new UserService(); var groupService = new GroupService(); var userGroupFacade = new UserGroupFacade(userService, groupService); // create an admin user in 1 call instead of havind to call UserService.CreateUser + GroupService.GetByName + GroupService.AddUserIntoGroup userGroupFacade.CreateAdminUser("Nicolas");