EF Code first Multi level inheritence issues - entity-framework

Question

I have a multi level inheriance heriarchy consisting of the following classes:
public abstract class BasePoco
{
[Key]
[DatabaseGenerated(DatabaseGeneratedOption.Identity)]
public int Id { get; set; }
}
public class Activity : BasePoco
{
public ActivityType ActivityType { get; set; }
[MaxLength(1000)]
public string Description { get; set; }
}
Now there is a special type of Activity which is called a data capture activity.
Which is of two types: DataCaptureActivity and MasterDataCaptureActivity
public class DataCaptureActivityBase : Activity
{
[MaxLength(100)]
public string Title { get; set; }
}
Derived Classes :
[Table("DataCaptureActivities")]
public class DataCaptureActivity : DataCaptureActivityBase
{
public virtual DataCaptureActivityType DataCaptureActivityType { get; set; }
}
[Table("MasterDataCaptureActivities")]
public class MasterDataCaptureActivity : DataCaptureActivityBase
{
public virtual string SomeOtherField{ get; set; }
}
The problem is upon creating a migration, The column Title which should be a part of DataCaptureActivity is actually coming up as a part of the Activity table.
Please note that DataCaptureActivityBase should not be a table in my schema. It is just for holding the common parameters DataCaptureActivities table and its inherited types.
The Schema I am targeting is :
Activity
-------------------------------
Id | ActivityType | Description
DataCaptureActivity
--------------------------------
Id | Title
MasterDataCaptureActivity
--------------------------------
Id | Title | SomeOtherField

Answer 1

Your context is similar to this
public DbSet<Activity> Activity { get; set; }
public DbSet<DataCaptureActivity> DataCaptureActivities { get; set; }
public DbSet<MasterDataCaptureActivity> MasterDataCaptureActivities { get; set; }
What you are conceptually saying to EF is that DataCaptureActivity is an Activity and that MasterDataCaptureActivity is an Activity. On the database you are creating all the three entities.
With this model, the statement
context.Activities.ToList();
retrieve all the Activities (the union of the three sets).
To do it with your model, EF on the database will create the Activity table with a Discriminator. The table structures will be this (look at 1-1 relationships):
ExecuteNonQuery==========
CREATE TABLE [Activity] (
[Id] int not null identity(1,1)
, [ActivityType] int not null
, [Description] text null
, [Title] varchar(100) null
, [Discriminator] varchar(128) not null
);
ALTER TABLE [Activity] ADD CONSTRAINT [PK_Activity_7ea65be8] PRIMARY KEY ([Id])
ExecuteNonQuery==========
CREATE TABLE [DataCaptureActivities] (
[Id] int not null
, [DataCaptureActivityType] int not null
);
ALTER TABLE [DataCaptureActivities] ADD CONSTRAINT [PK_DataCaptureActivities_7ea65be8] PRIMARY KEY ([Id])
ExecuteNonQuery==========
CREATE TABLE [MasterDataCaptureActivities] (
[Id] int not null
, [SomeOtherField] text null
);
ALTER TABLE [MasterDataCaptureActivities] ADD CONSTRAINT [PK_MasterDataCaptureActivities_7ea65be8] PRIMARY KEY ([Id])
ExecuteNonQuery==========
CREATE INDEX [IX_Id] ON [DataCaptureActivities] ([Id])
ExecuteNonQuery==========
CREATE INDEX [IX_Id] ON [MasterDataCaptureActivities] ([Id])
ExecuteNonQuery==========
ALTER TABLE [DataCaptureActivities] ADD CONSTRAINT [FK_DataCaptureActivities_Activity_Id] FOREIGN KEY ([Id]) REFERENCES [Activity] ([Id])
ExecuteNonQuery==========
ALTER TABLE [MasterDataCaptureActivities] ADD CONSTRAINT [FK_MasterDataCaptureActivities_Activity_Id] FOREIGN KEY ([Id]) REFERENCES [Activity] ([Id])
Also, this statement
using (var context = new Context(GetConnection()))
{
context.DataCaptureActivities.Add(new DataCaptureActivity() {Description = "Description"});
context.SaveChanges();
}
Will generate this DML statements (2 insert statements!!!)
ExecuteDbDataReader==========
insert into [Activity]([ActivityType], [Description], [Title], [Discriminator])
values (#p0, #p1, null, #p2);
select [Id]
from [Activity]
where [Id] = ##identity
#p0 = 0
#p1 = Description
#p2 = DataCaptureActivity
ExecuteNonQuery==========
insert into [DataCaptureActivities]([Id], [DataCaptureActivityType])
values (#p0, #p1);
#p0 = 1
#p1 = 0
The solution to target your tables
You need to change your model saying that DataCaptureActivities and MasterDataCaptureActivities are not Activities.
For example:
public abstract class BasePoco
{
[Key]
[DatabaseGenerated(DatabaseGeneratedOption.Identity)]
public int Id { get; set; }
}
public class BaseActivity : BasePoco
{
public ActivityType ActivityType { get; set; }
[MaxLength(1000)]
public string Description { get; set; }
}
[Table("Activity")]
public class Activity : BaseActivity
{
}
public class DataCaptureActivityBase : BaseActivity
{
[MaxLength(100)]
public string Title { get; set; }
}
[Table("DataCaptureActivities")]
public class DataCaptureActivity : DataCaptureActivityBase
{
public virtual DataCaptureActivityType DataCaptureActivityType { get; set; }
}
[Table("MasterDataCaptureActivities")]
public class MasterDataCaptureActivity : DataCaptureActivityBase
{
public virtual string SomeOtherField { get; set; }
}
In this case, the tables structures will be this
ExecuteNonQuery==========
CREATE TABLE [Activity] (
[Id] int not null identity(1,1)
, [ActivityType] int not null
, [Description] text null
);
ALTER TABLE [Activity] ADD CONSTRAINT [PK_Activity_2b28bd47] PRIMARY KEY ([Id])
ExecuteNonQuery==========
CREATE TABLE [DataCaptureActivities] (
[Id] int not null identity(1,1)
, [DataCaptureActivityType] int not null
, [Title] varchar(100) null
, [ActivityType] int not null
, [Description] text null
);
ALTER TABLE [DataCaptureActivities] ADD CONSTRAINT [PK_DataCaptureActivities_2b28bd47] PRIMARY KEY ([Id])
ExecuteNonQuery==========
CREATE TABLE [MasterDataCaptureActivities] (
[Id] int not null identity(1,1)
, [SomeOtherField] text null
, [Title] varchar(100) null
, [ActivityType] int not null
, [Description] text null
);
ALTER TABLE [MasterDataCaptureActivities] ADD CONSTRAINT [PK_MasterDataCaptureActivities_2b28bd47] PRIMARY KEY ([Id])
But in this case, if you want to enum all the ActivityBase you need to join them (Union) on the client.

Answer 2

Try doing the below steps.
Mark Activity class with a Table Attribute
Mark DataCaptureActivityBase as abstract
In OnModelCreating Map Derived Entities with MapInheritedProperties();
Hope this helps