title: ASP.NET core 3.1 :Adding Classes Libraries to the Project_ MissingMethodException: Method not found: 'Boolean Microsoft.EntityFrameworkCore.Migrations
body: <p>I'm working on <code>asp.net-core 3.1</code> project, I have added 3 Class Library for my project to separate Access Data, Models class and Utility classes I resolved problems of matching folders etc. But when I run my project I get this Error:</p>
  <pre><code>MissingMethodException: Method not found: 'Boolean Microsoft.EntityFrameworkCore.Migrations.IMigrationsModelDiffer.HasDifferences(Microsoft.EntityFrameworkCore.Metadata.IModel, Microsoft.EntityFrameworkCore.Metadata.IModel)'.
  
  
     Microsoft.AspNetCore.Diagnostics.EntityFrameworkCore.DatabaseErrorPageMiddleware.Invoke(HttpContext 
     httpContext)
     System.Runtime.CompilerServices.AsyncMethodBuilderCore.Start&lt;TStateMachine&gt;(ref TStateMachine 
     stateMachine)
     System.Runtime.CompilerServices.AsyncTaskMethodBuilder.Start&lt;TStateMachine&gt;(ref TStateMachine 
     stateMachine)
     Microsoft.AspNetCore.Diagnostics.EntityFrameworkCore.DatabaseErrorPageMiddleware.Invoke(HttpContext 
     httpContext)
     Microsoft.AspNetCore.Diagnostics.DeveloperExceptionPageMiddleware.Invoke(HttpContext context)  
  </code></pre>