Entity Framework 6 composite key (DateTime + foreign key) - database

Question

I have to store the following entities in a database:
devices
measuring points
measured values
where each device has one or more measuring points. The measured values table will store values for each measuring point every 10 minutes. This table will have millions of records after a few years and must be efficiently searchable by measuring point and timestamp. How would you design this with EF6 Code-First?
My first approach was:
public class Device
{
public int ID { get; set; }
public int DeviceNumber { get; set; }
...
public virtual ICollection<MeasuringPoint> MeasuringPoints { get; set; }
}
public class MeasuringPoint
{
public int ID { get; set; }
public int MeasuringPointNumber { get; set; }
...
// Foreign key
public int DeviceID { get; set; }
public virtual Device Device { get; set; }
}
public class MeasuredValue
{
//public int Id { get; set; } ????
public DateTime TimeStamp { get; set; }
// Foreign key
public int MeasuringPointID { get; set; }
public double Value;
public virtual MeasuringPoint MeasuringPoint { get; set; }
}
All values in the measured values table must be unique in the combination of TimeStamp and MeasuringPointID. What primary key should I define for MeasuredTable?

Answer 1

this is not uniquely code_first/EF related.
With EF you may choose a PK that will lead to the creation of a cluster index. Then you may/must create specific index(es) for the querie(s)
Imho, you may :
use an identity pk (faster insert)
create a (covering) index (point, date)
create a (covering) index (date, point)
use a pk (point, counter), where counter is identity or something like (max for point) + 1, or even the date (but what if 2 measures in the same millisecond ?).
create an index (date, point)
According to your transactional and concurrency pressure the maxsolution may be quite hard to implement.
In this last case you'll have a configuration like:
public class MeasuredValueConfiguration : EntityTypeConfiguration<MeasuredValue>{
public MeasuredValueConfiguration()
: base() {
/* ... */
HasKey(e => new {e.MeasuringPointID, e.Id});
/* ... */
}
}