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Over the last few days I've been restructuring and existing application of mine written in C# to use Entity Framework instead of the custom data access layer I made. All was going well until I ran into a particular POCO.

This POCO has 6 properties, 4 of which are basic types, however the last 2 are giving me trouble because they are other existing POCOs. The reason this gives me trouble is because using Linq to Entity does not work correctly when trying to use Entity Framework to access my database.

Error given: "An error occurred while executing the command definition. See the inner exception for details." InnerException: "InnerException = {"Invalid column name 'Course_CourseId'.\r\nInvalid column name 'Student_StudentId'.\r\nInvalid column name 'Staff_StaffId'."}"

My Database structure is:

UniversityCatalog
 Table: Courses
  -Field: CourseId (Guid)
  -Field: CourseName (String)
  -Field: CourseNumber (String)
  -Field: Comments (String)
  -Field: CreditHours (int)
  -Field: CourseTypeId (int) (ForeignKey: CourseTypes.CourseTypeId)
 Table: CourseTypes
  -Field: CourseTypeId (int)
  -Field: CourseTypeName (String)
 Table: Staffs
  -Field: StaffId (Guid)
  -Field: FirstName (String)
  -Field: LastName (String)
  -Field: EmployeeId (int)
 Table: Students
  -Field: StudentId (Guid)
  -Field: FirstName (String)
  -Field: LastName (String)
  -Field: Grade (String)
 Table: CourseOfferings
  -Field: CourseOfferingId (Guid)
  -Field: CourseId (Guid) (ForeignKey: Courses.CourseId)
  -Field: StaffId (Guid) (ForeignKey: Staffs.StaffId)
  -Field: Start Time (String)
  -Field: End Time (String)
  -Field: DayOfWeek (String)
 Table: CourseRegistrations
  -Field: CourseOfferingId (ForeignKey: CourseOfferings.CourseOfferingId)
  -Field: StudentId (ForeignKey: Students.StudentId)

The POCO I have for the CourseOfferings Table is: 

public class CourseOffering
{
    public Guid CourseOfferingId { get; set; }
    public String DayOfWeek { get; set; }
    public String StartTime { get; set; }
    public String EndTime { get; set; }
    public Course Course { get; set; }
    public Student Student { get; set; }
    public Staff Staff { get; set; }
}

I suspect I'd have to do some custom mapping in my context file, however I have no idea what I'd be doing. Any tips or pointer would help me greatly! Thanks!

(Also here's my context file:)

class GatewayContext: DbContext
{
    public DbSet<Course> Course { get; set; }
    public DbSet<CourseType> CourseTypes { get; set; }
    public DbSet<CourseOffering> CourseOfferings { get; set; }
    public DbSet<Staff> Staff { get; set; }
    public DbSet<Student> Students { get; set; }
}

Note: This is just a mock project to practice using these technologies

share|improve this question
    
"does not work correctly" isn't helpful. Please do post the actual compilation error message / runtime exception. –  ken2k Jun 11 '13 at 14:34
    
Yeah, sorry I forgot to include that. I've updated the question with the error message and exception. –  NightW. Jun 11 '13 at 14:38
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2 Answers

up vote 1 down vote

The easiest way is to download and install the Entity Framework Power Tools, then just reverse engineer your database to a Code First model with POCO's. Simple, easy, takes about 2 minutes.

The only drawback (I don't see it as such) is that EFPT reverses your model to an entirely fluent configured model, rather than using attributes. I don't like attributes though, so it's fine for me.

share|improve this answer
    
This is a possible solution, however I'd like to avoid using power tools to generate the code if possible. I'm currently trying to learn how to do this by hand since I'm new to the framework and I usually pick things up best like that. Thank you for the answer though! –  NightW. Jun 11 '13 at 14:51
    
@NightW. - using Power tools, you can look at the code and see what it's doing. –  Erik Funkenbusch Jun 11 '13 at 14:53
    
Yes, though it doesn't help me as much. The other issue I had with this though is that person who assigned me the mock project said to specifically leave the POCOs as they were as much as possible. Though I'm not entirely sure why he said that. In the previous code they were used as transfer objects. –  NightW. Jun 11 '13 at 14:58
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up vote 1 down vote

I believe the issue may be with your navigation properties to other entities. You may need to include the virtual keyword to allow entity framework to override these properties with proxies so you can access them as foreign keys.

public class CourseOffering
{
    public Guid CourseOfferingId { get; set; }
    public String DayOfWeek { get; set; }
    public String StartTime { get; set; }
    public String EndTime { get; set; }

    public Guid CourseId { get; set; }
    public Guid StudentId { get; set; }
    public Guid StaffId { get; set; }

    public virtual Course Course { get; set; }
    public virtual Student Student { get; set; }
    public virtual Staff Staff { get; set; }
}

On the other hand I have found that you may not be able to use a Guid as a Primary Key field.

http://social.msdn.microsoft.com/Forums/en-US/adodotnetentityframework/thread/37fd6405-3441-4b2b-82f6-266b79d86708

share|improve this answer
    
Making this change results in the inner exception of "InnerException = {"Invalid column name 'StudentId'."}". If that's the case, would it effect any of my other POCOs? They all use Guids as a primary, don't they? –  NightW. Jun 11 '13 at 14:55
    
Are you trying to use code first? If you have an existing database then I'd just create an EF Model based on it and see what properties it creates. If it's still not working then you could add the code in the following demo to get it working geekswithblogs.net/danemorgridge/archive/2010/02/12/… –  Stokedout Jun 11 '13 at 15:18
    
I guess I'll have to experiment with that. –  NightW. Jun 11 '13 at 15:44
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