Question

I am using Fluent NHibernate on sqlserverce.
Using NHibernate QueryOver I try to retrieve a row – NHibernate generate automatically a a join query
and I get the following Exception:

[SQL: SELECT tag FROM CheckpointToProtectionGroup cp2pg 
      JOIN CheckpointStorageObject cp ON cp.id = cp2pg.checkpoint_id 
      JOIN ProtectionGroupCheckpointStorageObject pg ON pg.id = cp2pg.vpg_id 
      WHERE cp.CheckpointIdentifierIdentifier = 1111  AND 
            pg.ProtectionGroupIdentifierGroupGuid = 
               11111111-1111-1111-1111-111111111111]
---> System.Data.SqlServerCe.SqlCeException: 
     The conversion is not supported. 
     [ Type to convert from (if known) = uniqueidentifier, 
       Type to convert to (if known) = numeric ]

From what I see, it seems that it tries to convert the value – 11111111-1111-1111-1111-111111111111 to numeric but this value is a Guid field:

CheckpointToProtectionGroup checkpointToProtectionGroup = Session
            .QueryOver<CheckpointToProtectionGroup>()
            .JoinQueryOver( row => row.ProtectionGroup)
            .Where(row => row.ProtectionGroupIdentifier.GroupGuid == 
                   protectionGroupIdentifier.GroupGuid)
            .SingleOrDefault();

ProtectionGroupIdentifier.GroupGuid is of Guid type

Answer 1

Looks like your GroupGuid value is not correctly converted to SQL. It should have single quotes around the value.

pg.ProtectionGroupIndentifierGroupGuidId = '11111111-1111-1111-1111-111111111111'

SQL Server tried to convert left hand value from uniqueidentifier (Guid) to numeric, since the right hand value is numeric value – numeric subtract operation with few operands.

You have protectionGroupIdentifier.GroupGuid value in Where part of your QueryOver expression. Check if GroupGuid is indeed Guid property. If it’s an object property, cast it to Guid.