Code First Migrations In Entity Framework Step By Step

Here are the steps:

  

Model Classes: Suppose you have the following two entities within your application.

public class Employee
{
    [Key]
    public int Id
    {
        get;
        set;
    }
    [Required]
    public string Code
    {
        get;
        set;
    }
    [Required]
    public string Name
    {
        get;
        set;
    }
    [Required]
    public string OptionType
    {
        get;
        set;
    }
    public bool Active
    {
        get;
        set;
    }
    public string Notes
    {
        get;
        set;
    }
    public ICollection < OptionsHistory > OptionsHistories
    {
        get;
        set;
    }
}
public class OptionsHistory
{
    [Key]
    public int Id
    {
        get;
        set;
    }
    public string Code
    {
        get;
        set;
    }
    public string Name
    {
        get;
        set;
    }
    public string OptionType
    {
        get;
        set;
    }
    public bool Active
    {
        get;
        set;
    }
    public string Notes
    {
        get;
        set;
    }
    public int OptionId
    {
        get;
        set;
    }
    public string OptionsVersion
    {
        get;
        set;
    }
    public Options Options
    {
        get;
        set;
    }
}

Here [Key] decorated column is a primary key column.

Mapping Details: DataContext class and Fluent API mapping details for above two entities are given below.

public class OptionCodeContext: DbContext
{
    public OptionCodeContext(): base("name=DbConnectionString")
    {

    }
    public DbSet < Options > options
    {
        get;
        set;
    }
    public DbSet < OptionsHistory > optionsHistories
    {
        get;
        set;
    }

    protected override void OnModelCreating(DbModelBuilder modelBuilder)
    {
        modelBuilder.Entity < Options > ().HasKey(p => p.Id);

        modelBuilder.Entity < Options > ().Property(c => c.Id)
            .HasDatabaseGeneratedOption(DatabaseGeneratedOption.Identity);

        modelBuilder.Entity < OptionsHistory > ().HasKey(b => b.Id);

        modelBuilder.Entity < OptionsHistory > ().Property(b => b.Id)
            .HasDatabaseGeneratedOption(DatabaseGeneratedOption.Identity);

        modelBuilder.Entity < OptionsHistory > ().HasRequired(p => p.Options)
            .WithMany(b => b.OptionsHistories).HasForeignKey(b => b.OptionId);

        base.OnModelCreating(modelBuilder);
    }
}

Connection String: And, your database connection string is given below:

<add name="DbConnectionString" connectionString="data source=SampleDataSource;initial catalog=OptionsCode;integrated security=True;MultipleActiveResultSets=True" providerName="System.Data.SqlClient" />

Visual Studio Package Manager Console: 

To create the database for these two entities within your application, go to the Package Manager Console option as shown below:

Creating New Database

Running Commands: Run the following command to configure migrations within your project and for creating new database.

1. Enable migrations
   
    Enable-Migrations
   
   
2. Create migration
   
   Add-Migration MigrationsName
   
   
3. Create upgrade/downgrade script
   
   Update-Database

When you run above listed command on the Package Manager Console windows one by one then: Firstly, a Migrations folder will be added into your applications having Configuration.cs file for Migrations configuration setting.

1. Secondly, a class file will be created having name suffix as MigrationsName followed by underscore and a unique generated number. This file will have all the entities to be created in the database.
   
   
2. Thirdly, a new database will be created having initial catalog name (initial catalog = YourDBName) as given in your connections string.

Suppose you have added one more class named as Customer into your data model classes

Now for updating the database with new changes run the following commands:

1. Create migration
   Add-Migration MigrationsName
   
   
2. Create upgrade/downgrade script
   Update-Database

When you run above listed command on the Package Manager Console windows one by one, then:

 

Firstly, a class file will be created having name suffix as MigrationsName followed by underscore and a unique generated number. This file will have all the entities to be created or updated in the database.

Undo/Rollback a Migrations

You can also Undo/Rollback specific migrations by using the following commands:

1. Rollback to a specific migrations
   Update-Database -TargetMigration:MigrationsName
   
   
2. Rollback all migrations
   Update-Database -TargetMigration:0