Question

Is it possible to map a table column to a class field instead to a class property and how?

YOU CAN DO IT 🙂

Follow this link: http://weblogs.asp.net/ricardoperes/archive/2013/08/22/mapping-non-public-members-with-entity-framework-code-first.aspx

This is a common request, and really makes sense; we need to use LINQ expressions and a bit of reflection magic. First, an helper function for returning an expression that points to a member:

      public static class ExpressionHelper
      {
          public static Expression<Func<TEntity, TResult>> GetMember<TEntity, TResult>(String memberName)
          {
              ParameterExpression parameter = Expression.Parameter(typeof(TEntity), "p");
              MemberExpression member = Expression.MakeMemberAccess(parameter, typeof(TEntity).GetMember(memberName, BindingFlags.Public | BindingFlags.NonPublic | BindingFlags.Instance).Single());
              Expression<Func<TEntity, TResult>> expression = Expression.Lambda<Func<TEntity, TResult>>(member, parameter);
              return (expression);
          }
     }

Then, we call it on the DbContext.OnModelCreating method, as a parameter to StructuralTypeConfiguration.Property:

  protected override void OnModelCreating(DbModelBuilder modelBuilder)
  {
      modelBuilder.Entity<Project>().Property(ExpressionHelper.GetMember<Project, Decimal>("Budget")).IsRequired();

      base.OnModelCreating(modelBuilder);
  }

Answer 1

Entity Framework (Code First or not) does not support mapping to a field; only to properties.

UPDATE
As pointed out in the comments, these documents are a bit dated but might still help any beginner along:

Entity Framework Code first development Resources and Documentation

For the sake of completeness, heres a link to whats included in EF 4.1 RC: EF 4.1 Release Candidate Available

Changes since CTP5 (From the link above):

• Rename of ‘DbDatabase’ to ‘Database’. This class has also moved
  to the ‘System.Data.Entity’
  namespace, along with the database
  initializer classes.

• Rename of ‘ModelBuilder’ to ‘DbModelBuilder’, to align with the
  other core classes.

• Validation in Model First and Database First. The new validation
  feature was only supported in Code
  First in CTP5. In RC the validation
  feature will work with all three
  development workflows (Model First,
  Database First, and Code First).

• Complete Intellisense docs. Feature CTPs were not extensively documented
  because the API surface was changing
  significantly between each release.
  This release includes complete
  documentation.

• Removal of Code First Pluggable Conventions. Pluggable Conventions
  were previewed in Feature CTP5 but
  were not at go-live quality for this
  release. This release still supports
  the removal of default conventions.

• Consolidation of IsIndependent in the Code First relationship API. When
  configuring relationships in Feature
  CTP5 the IsIndependent method was used
  to identify that the relationship did
  not have a foreign key property
  exposed in the object model. This is
  now done by calling the Map method.
  HasForeignKey is still used for
  relationships where the foreign key
  property is exposed in the object
  model.