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c#sqlnhibernatehqlinner-join
vgru
vgru

Reputation: 51274

HQL Path expected for join (when joining same table)

I am trying to get pairs of measurement for two different devices, joined on equal Timestamps. In SQL, this works as expected:

select
  leftItem.Timestamp, leftItem.Value, rightItem.Value
from
  DataTable leftItem
  inner join DataTable rightItem
  on leftItem.Timestamp = rightItem.Timestamp
where
  leftItem.Device = 1 and rightItem.Device = 2

But if I try to convert it to HQL:

select
  left, right 
from
  DataTable as left 
  inner join DataTable as right
  on left.Timestamp = right.Timestamp
where
  left.Device = 1 and right.Device = 2

I get a NHibernate.Hql.Ast.ANTLR.SemanticException:

Path expected for join!

How do I specify a "path" to the same table?

Upvotes: 4

Views: 3447

Answers (1)

JB Nizet
JB Nizet

Reputation: 692003

In HQL, joins can only be done on associations between entities. If you want a join on something else, the only possibility is to make the join in the where clause:

select left, right 
from
  DataTable as left, DataTable as right
where
  left.Timestamp = right.Timestamp
  and left.Device = 1 
  and right.Device = 2

Upvotes: 6

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