Relation between users with messages

Question

Hello,
I have a table of Users:
create table dbo.User
Id int identity not null,
Name nvarchar (400) null,
// Other coluns as Login, Password, etc.
create table dbo.Role
Id int identity not null,
Name nvarchar (20) null
create table dbo.UserRole
UserId int not null,
RoleId int not null
Each user has one or more roles.
I need to relate users one to each other in periods of type.
For example, one professor to its students during 4 months in 2015.
And I also need to track messages between users.
One of my ideas would be the following:
create table dbo.UserToUser
FirstUserId int not null,
SecondUserId int not null,
StartDate datetime not null,
EndDate datetime not null
Being both ProfessorId and StudentId FK's of Users table.
create table dbo.Message
ToId int not null,
FromId int not null,
Text nvarchar(max) not null,
Created datetime not null
Being both ToId and FromId FK's of Users table.
Should this be done in another way?
Thank You,

Answer 1

Review the following design:
create table dbo.Users
Id int identity PRIMARY KEY,
Name nvarchar (400)not null UNIQUE,
-- // Other coluns as Login, Password, etc.
create table dbo.Role
Id int identity PRIMARY KEY,
Name nvarchar (20) not null UNIQUE
create table dbo.UserRole
UserId int not null REFERENCES Users,
RoleId int not null REFERENCES Role,
PRIMARY KEY (UserId, RoleID)
create table dbo.UserToUser
FirstUserId int not null REFERENCES Users,
SecondUserId int not null REFERENCES Users,
StartDate datetime not null,
EndDate datetime not null,
PRIMARY KEY (StartDate, FirstUserID, SecondUserID)
create table dbo.Message
ToId int not null REFERENCES Users,
FromId int not null REFERENCES Users,
Text nvarchar(max) not null,
Created datetime not null,
PRIMARY KEY(ToId, FromId, Created)
Kalman Toth Database & OLAP Architect
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