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c#entity-framework-4ef-code-first
bryanjonker
bryanjonker

Reputation: 3406

Using existing database and EF code-first, mapping a lookup table to entity

I am using entity framework, code first, 4.0, hitting an existing legacy database for read-only access. The database is normalized, so 

 Table [Event]
      [ID]
      [Date_Entered]
      [Event_Status_Key]

 Table [Event_Status]
      [Event_Status_Key]
      [Event_Status_Description]

My class looks like 

 public class Event
 {
       public DateTime DateEntered { get; set; }
       public string StatusDescription { get; set; }
 }

This is a WCF service layer application.

My two questions:

  1. Is there any easy way to populate the status description without creating a second Dictionary-type object? I've seen questions like this: Entity Framework Mapping to Lookup table, but they seem to be focused on object to object, and I really just want a primitive. I'd prefer using the fluent API as opposed to attributes.

  2. When the data is loaded, is any of the data cached at the code layer? Or does each check on the StatusDescription mean a separate call on the [Event_Status] table?

Edit: A possible (more subjective, which is why I didn't bring it up) third question is how close should the data entities match the database. Is it always a one-to-one field/table? Is what I'm doing (joining two tables into one data entity obejct) bad?

Thanks.

Upvotes: 1

Views: 681

Answers (1)

Ladislav Mrnka
Ladislav Mrnka

Reputation: 364259

Entity framework expects that you will map both tables as separate entities and use projection in your query:

var query = from e in context.Events
            select new WcfEvent // Your original Event class is just DTO
                {
                     DateEntered = e.DateEntered,
                     StatusDescription = e.EventStatus.EventStatusDescription 
                };

This example expects correctly one-to-one mapping of your Event and Event_Status tables.

If you need any kind of caching you will have to implement it yourselves. Projected results are not even tracked by the context.

Upvotes: 1

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