Unable to create a DbContext' Error when Using EF Core in .NET 8 ClassLibrary Project

Question

Hello everyone, I've developed a ClassLibrary project using .NET 8 and C#, and I've utilized EF Core 8 in it. I've defined my own models and context within it. However, when I attempt to use the add-migration command, I encounter this error:

"Unable to create a 'DbContext' of type ''. The exception 'Unable to resolve service for type 'Microsoft.EntityFrameworkCore.DbContextOptions`1[ZSL.Database.ApplicationDBContext]' while attempting to activate 'ZSL.Database.ApplicationDBContext'.' was thrown while attempting to create an instance. For the different patterns supported at design time, see this link."

I would appreciate it if you could guide me on this issue.

Answer 1

Hi,@Kamyab Faghih. Welcome to Microsoft Q&A. 

Creating a database using DBContext in a .NET 8 ClassLibrary Project

Example(Assume that the database is Sql Server and the development tool is Visual Studio):

1.Create a .NET 8 ClassLibrary Project

2.Install Microsoft.EntityFrameworkCore.SqlServer, Microsoft.EntityFrameworkCore.Design, and Microsoft.EntityFrameworkCore.Tools through Nuget

3.Add entity class

    public class User

    {

        public int Id { get; set; }

 

        public string Name { get; set; }   

    }

4.Add DbContext Class (Write your database connection string)

public class MyDbContext:DbContext

{

    public MyDbContext() { }

 

    public MyDbContext(DbContextOptions<MyDbContext> options) : base(options)

    {

 

    }

 

    public DbSet<User> Users { get; set; }

 

 

    protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)

    {

        optionsBuilder.UseSqlServer("Write your database connection string");

    }

 

    protected override void OnModelCreating(ModelBuilder modelBuilder)

    {

        modelBuilder.Entity<User>(entity =>
        {

            entity.ToTable("User");
            entity.HasKey(p => p.Id).HasName("PK_User");

            entity.Property(p => p.Id)

            .HasColumnName("id")

            .HasColumnType("int").ValueGeneratedNever();

            entity.Property(p => p.Name)

            .HasColumnName("name");

        });

    }

}

5.Set the current project as startup project

6.Execute the command to generate the database

Way 1(Ensure that the current project can be built successfully):

a.Open Developer PowerShell-> Enter the current project

b.If dotnet ef is not installed, you need to execute this command

dotnet tool install --global dotnet-ef

c.Creating Migrations

dotnet ef migration add init

d.Update the database

dotnet ef database update

Way 2(Ensure that the solution can be built successfully):

a.  Open Tools->NuGet Package Manager-> Package Manager Console

b.  Set the Default Project as the current project

c.  Creating Migrations

Add-Migration Init

d.  Update the database

Update-Database

You can check your program against the above examples. If you can provide a simple example that causes the error, I will be able to answer your question more accurately.

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