Hello!
I wasn't really sure of what to call this post... Here's this situation, I
have this entity (simplified):
public class AnalogicalValues
{
public virtual DateTime Timestamp { get; set; }
public virtual Double ? Value { get; set; }
public virtual Int32 DeviceId { get; set; }
}
I want to be able to do something like this in SQL (simplified):
(SQL)
select (A.Value + B.Value) / 2, A.Timestamp
from AnalogicalValues A
full outer join AnalogicalValues B
on A.Timestamp = B.Timestamp
where A.DeviceId = 1
and B.DeviceId = 2
The problem is, although HQL supports full joins, it does not support
specifying a join path; so the following HQL query is invalid:
(HQL)
select (A.Value + B.Value) / 2, A.Timestamp
from AnalogicalValues A
full join AnalogicalValues B
with A.Timestamp = B.Timestamp
where A.DeviceId = 1
and B.DeviceId = 2
You may wonder why I need the full outer join: that is because I want to
group together values of the same time stamp, if and only if they exist on
both sides. And, yes, I need to do it in HQL.
Here's how I solved it:
public class AnalogicalValues
{
public virtual DateTime Timestamp { get; set; }
public virtual Double ? Value { get; set; }
public virtual Int32 DeviceId { get; set; }
public IEnumerable<AnalogicalValues> SameTimestamp { get; set; }
}
As you can see, I mapped a set collection from AnalogicalValues to
AnalogicalValues, and I joined it by the Timestamp property (using
property-ref).
This way, this HQL query works:
(HQL)
select (A.Value + B.Value) / 2, A.Timestamp
from AnalogicalValues A
full join A.SameTimestamp B
where A.DeviceId = 1
and B.DeviceId = 2
My question is: is this the best approach?
Thanks!
RP
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