Compare metadata through _metadata for HDAH objects

HistoryDatasetsAssoicationHistory objects don't have the full blown metadata
objects, instead we compare the raw JSON dumped into the database.

lib/galaxy/managers/jobs.py

@@ -135,22 +135,22 @@ def __search(self, tool_id, tool_version, user, input_data, input_ids=None, job_
                         a.dataset_id == b.id,
                         c.dataset_id == b.dataset_id,
                         c.id == v,  # c is the requested job input HDA
-                        # We can only compare input dataset names and metadata for a job
-                        # if we know that the input dataset hasn't changed since the job was run.
-                        # This is relatively strict, we may be able to lift this requirement if we record the jobs'
-                        # relevant parameters as JobParameters in the database
+                        # We can compare input dataset names and metadata for a job
+                        # if we know that the input dataset hasn't changed since the job was run,
+                        # or if the job recorded a dataset_version and name and metadata of the current
+                        # job request matches those that were recorded for the job in question (introduced in release 18.01)
                         or_(and_(
                             b.update_time < model.Job.create_time,
                             b.name == c.name,
                             b.extension == c.extension,
-                            b._metadata == c._metadata,
+                            b.metadata == c.metadata,
                         ), and_(
                             b.id == e.history_dataset_association_id,
                             a.dataset_version == e.version,
                             e.name == c.name,
                             e.extension == c.extension,
-                            e.metadata == c._metadata,
-                    )),
+                            e._metadata == c._metadata,
+                        )),
                         or_(b.deleted == false(), c.deleted == false())
                     ))
                     if identifier:

lib/galaxy/model/__init__.py

@@ -2675,7 +2675,12 @@ def __init__(self,
         self.version = version
         self.extension = extension
         self.extended_metadata_id = extended_metadata_id
-        self.metadata = metadata
+        if isinstance(metadata['dbkey'], list):
+            # The dbkey may or may not be stored in a list.
+            # To facilitate comparison we use the raw value
+            metadata = metadata.copy()
+            metadata['dbkey'] = metadata['dbkey'][0]
+        self._metadata = metadata
 
 
 class HistoryDatasetAssociationDisplayAtAuthorization(object):

lib/galaxy/model/mapping.py

@@ -157,7 +157,7 @@
     Column("version", Integer),
     Column("name", TrimmedString(255)),
     Column("extension", TrimmedString(64)),
-    Column("metadata", MetadataType()),
+    Column("metadata", MetadataType(), key="_metadata"),
     Column("extended_metadata_id", Integer, ForeignKey("extended_metadata.id"), index=True),
 )