Entity Mappings using Fluent API in EF 6

The Fluent API can be used to configure an entity to map it with database table(s), default schema, etc.

Configure Default Schema

First, let's configure a default schema for the tables in the database. However, you can change the schema while creating the individual tables. The following example sets the Admin schema as a default schema. All the database objects will be created under the Admin schema unless you specify a different schema explicitly.

public class SchoolContext: DbContext 
{
    public SchoolDBContext(): base() 
    {
    }

    public DbSet<Student> Students { get; set; }
    public DbSet<Standard> Standards { get; set; }
        
    protected override void OnModelCreating(DbModelBuilder modelBuilder)
    {
        //Configure default schema
        modelBuilder.HasDefaultSchema("Admin");
    }
}

Map Entity to Table

Code-First will create the database tables with the name of DbSet properties in the context class, Students and Standards in this case. You can override this convention and give a different table name than the DbSet properties, as shown below.

namespace CodeFirst_FluentAPI_Tutorials
{
    public class SchoolContext: DbContext 
    {
        public SchoolDBContext(): base() 
        {
        }

        public DbSet<Student> Students { get; set; }
        public DbSet<Standard> Standards { get; set; }
        
        protected override void OnModelCreating(DbModelBuilder modelBuilder)
        {
            //Configure default schema
            modelBuilder.HasDefaultSchema("Admin");
                    
            //Map entity to table
            modelBuilder.Entity<Student>().ToTable("StudentInfo");
            modelBuilder.Entity<Standard>().ToTable("StandardInfo","dbo");
        }
    }
}

As you can see in the above example, we start with the Entity<TEntity>() method. Most of the time, you have to start with the Entity<TEntity>() method to configure it using Fluent API. We have used the ToTable() method to map the Student entity to the StudentInfo table and the Standard entity to the StandardInfo table. Notice that StudentInfo is in the Admin schema and the StandardInfo table is in the dbo schema because we have specified the dbo schema for the StandardInfo table.

Map Entity to Multiple Tables

The following example shows how to map the Student entity to multiple tables in the database.

namespace CodeFirst_FluentAPI_Tutorials
{
    public class SchoolContext: DbContext 
    {
        public SchoolDBContext(): base() 
        {
        }

        public DbSet<Student> Students { get; set; }
        public DbSet<Standard> Standards { get; set; }
        
        protected override void OnModelCreating(DbModelBuilder modelBuilder)
        {
            modelBuilder.Entity<Student>().Map(m =>
            {
                m.Properties(p => new { p.StudentId, p.StudentName});
                m.ToTable("StudentInfo");
            }).Map(m => {
                m.Properties(p => new { p.StudentId, p.Height, p.Weight, p.Photo, p.DateOfBirth});
                m.ToTable("StudentInfoDetail");
            });

            modelBuilder.Entity<Standard>().ToTable("StandardInfo");
        }
    }
}

As you can see in the above example, we mapped some properties of the Student entity to the StudentInfo table and other properties to the StudentInfoDetail table using the Map() method. Thus, the Student entity will split into two tables, as shown below.

The Map() method requires a delegate method parameter. You can pass an Action delegate or a lambda expression in the Map() method, as shown below.

using System.Data.Entity.ModelConfiguration.Configuration;

namespace CodeFirst_FluentAPI_Tutorials
{
    public class SchoolContext: DbContext 
    {
        public SchoolDBContext(): base() 
        {
        }

        public DbSet<Student> Students { get; set; }
        public DbSet<Standard> Standards { get; set; }
        
        protected override void OnModelCreating(DbModelBuilder modelBuilder)
        {
            modelBuilder.Entity<Student>().Map(delegate(EntityMappingConfiguration<Student> studentConfig)
            {
                studentConfig.Properties(p => new { p.StudentId, p.StudentName });
                studentConfig.ToTable("StudentInfo");
            });

            Action<EntityMappingConfiguration<Student>> studentMapping = m =>
            {
                m.Properties(p => new { p.StudentId, p.Height, p.Weight, p.Photo, p.DateOfBirth });
                m.ToTable("StudentInfoDetail");
            };
            
            modelBuilder.Entity<Student>().Map(studentMapping);
            modelBuilder.Entity<Standard>().ToTable("StandardInfo");
        }
    }
}