Entity Framework Code First: Mapping to Existing Table in the Database

Introduction

This tip is about how to connect with an existing table in the database.

Background

For learning Code First, you can refer to the following:

• Entity Framework Code First: Let's Try It
• Code First Approach using Entity Framework 4.1, Inversion of Control, Unity Framework, Repository & Unit of Work Pattern and MVC3 Razor View
• CRUD Operations Using Entity Framework 5.0 Code First Approach in MVC
• Code First with Entity Framework 5 using MVC4 and MVC Scaffold

Using the Code

The database name is MyClass and it consists of only one table "ClassAll".

Below is ClassAll class with the same attributes and properties as of the table .

using System;
using System.Collections.Generic;
using System.ComponentModel.DataAnnotations;

namespace School.Data.Model
{
    public partial class ClassAll
    {
          
        public int SchoolRollNo { get; set; }
        public int Standard { get; set; }
        public int ClassRollNo { get; set; }
        public string Name { get; set; }
        public string Gender { get; set; }
        public int Percentage { get; set; }
        public System.DateTime Date { get; set; }
    }
}

The class ClassAllMap is used to map with the existing table in the database.

using System.ComponentModel.DataAnnotations.Schema;
using System.Data.Entity.ModelConfiguration;

namespace School.Data.Model.Mapping
{
    public class ClassAllMap : EntityTypeConfiguration<ClassAll>
    {
        public ClassAllMap()
        {
            // Primary Key
            this.HasKey(t => t.SchoolRollNo);

            // Properties
            this.Property(t => t.SchoolRollNo)
                .HasDatabaseGeneratedOption(DatabaseGeneratedOption.None);

            this.Property(t => t.Name)
                .IsRequired()
                .HasMaxLength(50);

            this.Property(t => t.Gender)
                .IsRequired()
                .IsFixedLength()
                .HasMaxLength(10);

            // Table & Column Mappings
            this.ToTable("ClassAll");
            this.Property(t => t.SchoolRollNo).HasColumnName("SchoolRollNo");
            this.Property(t => t.Standard).HasColumnName("Standard");
            this.Property(t => t.ClassRollNo).HasColumnName("ClassRollNo");
            this.Property(t => t.Name).HasColumnName("Name");
            this.Property(t => t.Gender).HasColumnName("Gender");
            this.Property(t => t.Percentage).HasColumnName("Percentage");
            this.Property(t => t.Date).HasColumnName("Date");
        }
    }
}

MyClassContext is the reference to the "MySchool" database. In this code, we are using the ClassAllMap declared above for configuration.

using System.Data.Entity;
using System.Data.Entity.Infrastructure;
using School.Data.Model.Mapping;

namespace School.Data.Model
{
    public partial class MyClassContext : DbContext
    {
        static MyClassContext()
        {
            Database.SetInitializer<MyClassContext>(null);
        }

        public MyClassContext()
            : base("Name=MyClassContext")
        {
        }

        public DbSet<ClassAll> ClassAlls { get; set; }

        protected override void OnModelCreating(DbModelBuilder modelBuilder)
        {
            modelBuilder.Configurations.Add(new ClassAllMap()); 
        }
    }
}

If using SQL Server Express Edition, in web.config file, add the connection string as follows:

<connectionStrings> 
    <add name="MyClassContext" providerName="System.Data.SqlClient" 
       connectionString="Server=.\SQLEXPRESS;Database=MyClass;Trusted_Connection=true;" />
</connectionStrings>