ASP.NET Core Web API Error: Model 1[TContext] violates the Constraint of type 'TContext' - asp.net-core

Question

I have a Solution in Visual Studio 2017 that contains the following Projects:
CredentialManager.API (ASP.NET Core 2.1 Web API project)
CredentialManager.Models (Class Library that contains the Domain Model and Data Context Class)
The Domain Model Class is coded as follows:
using System.ComponentModel.DataAnnotations;
using System.ComponentModel.DataAnnotations.Schema;
namespace CredentialManager.Models.Entities
{
public class Credential
{
[Key]
[DatabaseGenerated(DatabaseGeneratedOption.Identity)]
public long CredentialId { get; set; }
[Required]
public string Username { get; set; }
[Required]
public string Password { get; set; }
[Required]
public string Application { get; set; }
}
}
The Data Context Class is as follows:
using System;
using System.Collections.Generic;
using System.Text;
using CredentialManager.Models.Entities;
using Microsoft.EntityFrameworkCore;
namespace CredentialManager.Models.Context
{
public class CredentialManagerContext : DbContext
{
public CredentialManagerContext(DbContextOptions options)
: base(options)
{ }
public DbSet<Credential> Credentials { get; set; }
}
}
The appsettings.json file looks like the following:
{
"Logging": {
"LogLevel": {
"Default": "Warning"
}
},
"ConnectionStrings": {
"i.": null,
"CredentialManagerDB": "server=.\\SQLEXPRESS;database=CredentialManagerDB;Trusted_Connection=true;"
},
"AllowedHosts": "*"
}
The Startup.CS file looks like this:
// This method gets called by the runtime. Use this method to add services to the container.
public void ConfigureServices(IServiceCollection services)
{
services.AddMvc().SetCompatibilityVersion(CompatibilityVersion.Version_2_1);
services.AddDbContext<CredentialManagerContext>(o => o.UseSqlServer(Configuration["ConnectionStrings:CredentialManagerDB"]));
// In production, the Angular files will be served from this directory
services.AddSpaStaticFiles(configuration =>
{
configuration.RootPath = "ClientApp/dist";
});
}
I then build the Solution and Added Migrations. But when I run update-database, I get the following error:
GenericArguments[0], 'CredentialManager.Models.Migrations.CredentialManagerContext', on 'Microsoft.EntityFrameworkCore.Design.IDesignTimeDbContextFactory`1[TContext]' violates the constraint of type 'TContext'.
Can someone here throw some light on this error ? If I include the classes and data context in the same folder as the API project, then everything works.. But I want these classes to be part of a separate Class Library Project. Any help would be much appreciated.
Thanks.

Answer 1

Update context file to have the following:
public CredentialManagerContext(DbContextOptions<CredentialManagerContext> options)
: base(options)
{ }
As outlined in the documentation:
This requires adding a constructor argument to your DbContext type that accepts :
DbContextOptions<TContext>
This should resolve your issue.

Answer 2

Thank you for all the suggestions. I found a Solution as well. The Startup.cs needs to be informed about the Project that contains the Migrations:
services.AddDbContext<CredManagerContext>(options => options.UseSqlServer(Configuration.GetConnectionString("CredentialManagerDB"), x => x.MigrationsAssembly("CredManager.Models")));
Everything works perfectly after this.