title: The model already has an element that has the same name - ASP.NET
body: <p>I'm working with ASP.Net web application and whenever I tried to add a <code>FOREIGN KEY</code> this error appears in the Data tools operations : </p>
  
  <blockquote>
    <p>SQL71508 :: The model already has an element that has the same name
    dbo.FK_Sellers_Users. SQL71508 :: The model already has an element
    that has the same name dbo.FK_Sellers_Users.</p>
  </blockquote>
  
  <p>I don't understand what's the problem with FK! I have 2 tables with this error </p>
  
  <p>table <code>Sellers</code> :</p>
  
  <pre><code>CREATE TABLE [dbo].[Sellers] (
      [Seller_ID]     INT           IDENTITY (1, 1) NOT NULL,
      [Name]          NVARCHAR (50) NOT NULL,
      [SUsername]      NVARCHAR (50) NOT NULL,
      [Password]      NVARCHAR (50) NOT NULL,
      [SEmail]         NVARCHAR (50) NOT NULL,
      [Phone]         NVARCHAR (50) NOT NULL,
      [City]          NVARCHAR (50) NOT NULL,
      [LastLoginDate] DATETIME      NULL,
      [CreatedDate]   DATETIME      NULL,
      PRIMARY KEY CLUSTERED ([Seller_ID] ASC), 
      CONSTRAINT [FK_Sellers_Users] FOREIGN KEY ([SEmail]) REFERENCES [Users]([Email]), 
      CONSTRAINT [FK_Sellers_Users] FOREIGN KEY ([SUsername]) REFERENCES [Users]([Username])
  );
  </code></pre>
  
  <p>and table <code>Users</code> : </p>
  
  <pre><code>CREATE TABLE [dbo].[Users] (
      [Id]       INT           NOT NULL IDENTITY,
      [Username] NVARCHAR (50) NOT NULL,
      [Password] NVARCHAR (50) NOT NULL,
      [Email]    NVARCHAR (50) NOT NULL,
      [UserType] INT    NULL,
      PRIMARY KEY CLUSTERED ([Id]), 
      CONSTRAINT [AK_Users_Username] UNIQUE ([Username]), 
      CONSTRAINT [AK_Users_Email] UNIQUE ([Email]),
  );
  </code></pre>