如何在 Entity Framwowrk Core 中为代码优先方法创建一个新表

Question

Initially I started with the below code

public class ShareMyBlogPostContext : DbContext
{
   public ShareMyBlogPostContext(DbContextOptions<ShareMyBlogPostContext> options):base(options)
   {
   }

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

And I ran the below commands to create the database table and migrations:

dotnet ef migrations add InitialDb
dotnet ef database update

But after some time, I realized that I need to have a new entity and I updated my DbContext class as below:

public class ShareMyBlogPostContext : DbContext
{
   public ShareMyBlogPostContext(DbContextOptions<ShareMyBlogPostContext> options) : base(options)
   { }

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

Since I was just starting out the project and there was not much data in Users table, it was not a big task for me to delete the already existing Users table from the database and Migrations folder from my project, and re-executing the above commands. This way I was able to create a new database table named Blogs .

But how to create a new database table of the newly added entity in the DbContext without removing the existing tables and migrations? As this would not be the scenario every time.

Answer 1

hi please type this command

dotnet ef migrations add AddBlogs
dotnet ef database update

for more please visit this Page

also if you want to keep your table you must be change migration.cs files manual to add your tables and fields and just run this command

dotnet ef database update

Answer 2

EF always looks inside DbContext derived class ( ShareMyBlogPostContext in your case) to detect changes. Sometimes you may not add separate DbSet instance for a newely created class, never mind, if you make a relationship between this newly created class and one of DbSet classes, the required tables will be appeared just after you request it . Every thing in EF codefirst is fully-managed and nothing will happen unless you run migrations add migrationName (.net CLI command) in order to generate script for current changes. Based on your configuration , there may no migration to be applied unless you request it by database update . In this way, you may have multiple migrations, the command Updates the database schema based on the last migration snapshot .

Dealing with database changes is a critical parts of any project. So, please read EF document before.