Entity Framework Code First, database creation problem, what should I do?

Question

ASP.NET

I have classes:

public class Topic
    {
        public int Id { get; set; }

        public string Name { get; set; }

        public string Description { get; set; }

        public DateTime Time { get; set; }

        public List<Lesson> Lessons { get; set; }

        public List<string> Tags { get; set; }

        public Topic()
        {
            Lessons = new List<Lesson>();

            Tags = new List<string>();
        }
    }
public class Lesson
    {
        public int Id { get; set; }

        public int TopicId { get; set; }

        public Topic Topic { get; set; }

        public string Name { get; set; }

        public List<Paragraph> Paragraphs { get; set; }

        public List<LTask> Tasks { get; set; }

        public Lesson()
        {
            Paragraphs = new List<Paragraph>();

            Tasks = new List<LTask>();
        }
    }
public class LTask
    {
        public int Id { get; set; }

        public int LessonId { get; set; }

        public Lesson Lesson { get; set; }

        public string HeadLine { get; set; }

        public string Question { get; set; }

        public string Answer { get; set; }
    }
public class Paragraph
    {
        public int Id { get; set; }

        public int LessonId { get; set; }

        public Lesson Lesson { get; set; }

        public string HeadLine { get; set; }

        public string Text { get; set; }
    }

And also the context:

public class CourseContext : DbContext
    {
        public CourseContext()
            : base("name=CourseContext")
        {
        }

        public DbSet<Topic> Topics { get; set; }

        public DbSet<string> Tags { get; set; }

        public DbSet<Lesson> Lessons { get; set; }

        public DbSet<Paragraph> Paragraphs { get; set; }

        public DbSet<LTask> Tasks { get; set; }
    }

But when I run the application, I get an error: "Type 'System.String' has not been mapped. Verify that the type has not been explicitly excluded using the Ignore method or the NotMappedAttribute data annotation. Verify that the type is defined as a class, not a primitive type, or generic type, and also does not inherit from EntityObject."
Can you help with solving this problem? I tried to solve it myself, but I couldn't.

Answer 1

Make Tags as a class with Id, Tag fields and specify it in links

Answer 2

It's just that you can't use standard data types in DbSet, only classes created by you