Entity Framework .Include() with compile time checking?

Question

Consider the following code, which is calling against an EF generated data context:

var context = new DataContext();
var employees = context.Employees.Include("Department");

If I change the name of the Department relationship then this code is going to start throwing a runtime error. So is there any way to call the .Include() method in a safe manner, so I get compile time checking for all the relationships being referenced?

Answer 1

I did a little extension to ObjectQuery which goes like this

public static ObjectQuery<TEntity> Include<TEntity, TProperty>(this ObjectQuery<TEntity> query, Expression<Func<TEntity, TProperty>> expression) where TEntity : class
{
    string name = expression.GetPropertyName();
    return query.Include(name);
}

which also requires

public static class ExpressionExtensions
{
    public static string GetPropertyName<TObject, TProperty>(this Expression<Func<TObject, TProperty>> expression) where TObject : class
    {
        if (expression.Body.NodeType == ExpressionType.Call)
        {
            MethodCallExpression methodCallExpression = (MethodCallExpression)expression.Body;
            string name = ExpressionExtensions.GetPropertyName(methodCallExpression);
            return name.Substring(expression.Parameters[0].Name.Length + 1);
        }
        return expression.Body.ToString().Substring(expression.Parameters[0].Name.Length + 1);
    }

    private static string GetPropertyName(MethodCallExpression expression)
    {
        MethodCallExpression methodCallExpression = expression.Object as MethodCallExpression;
        if (methodCallExpression != null)
        {
            return GetPropertyName(methodCallExpression);
        }
        return expression.Object.ToString();
    }
}

with that you can do

var context = new DataContext();      
var employees = context.Employees.Include(e => e.Department);

which is going to be check at compile time. If i remember correctly, this methods doesn't work for many-to-many relationship but it works for stuff like

var item = context.Employees.Include(e => e.Department.Manager);

Good luck to you