Add an index to columns of DbLink for SqlAlchemy

aiida/backends/djsite/db/models.py

@@ -224,41 +224,18 @@ def __str__(self):
 
 @python_2_unicode_compatible
 class DbLink(m.Model):
-    """
-    Direct connection between two dbnodes. The label is identifying the
-    link type.
-    """
+    """Direct connection between two dbnodes. The label is identifying thelink type."""
+
     # If I delete an output, delete also the link; if I delete an input, stop
     # NOTE: this will in most cases render a DbNode.objects.filter(...).delete()
     # call unusable because some nodes will be inputs; Nodes will have to
     #    be deleted in the proper order (or links will need to be deleted first)
-    input = m.ForeignKey('DbNode', related_name='output_links',
-                         on_delete=m.PROTECT)
-    output = m.ForeignKey('DbNode', related_name='input_links',
-                          on_delete=m.CASCADE)
-    # label for data input for calculation
+    # The `input` and `output` columns do not need an explicit `db_index` as it is `True` by default for foreign keys
+    input = m.ForeignKey('DbNode', related_name='output_links', on_delete=m.PROTECT)
+    output = m.ForeignKey('DbNode', related_name='input_links', on_delete=m.CASCADE)
     label = m.CharField(max_length=255, db_index=True, blank=False)
     type = m.CharField(max_length=255, db_index=True, blank=True)
 
-    class Meta:
-        # I cannot add twice the same link
-        # I want unique labels among all inputs of a node
-        # NOTE!
-        # I cannot add ('input', 'label') because in general
-        # if the input is a 'data' and I want to add it more than
-        # once to different calculations, the different links must be
-        # allowed to have the same name. For calculations, it is the
-        # responsibility of the output plugin to avoid to have many
-        # times the same name.
-        #
-        # A calculation can have both a 'return' and a 'create' link to
-        # a single data output node, which would violate the unique constraint
-        # defined below, since the difference in link type is not considered.
-        # The distinction between the type of a 'create' and a 'return' link is not
-        # implemented at the moment, so the unique constraint is disabled.
-        # unique_together = ("output", "label")
-        pass
-
     def __str__(self):
         return "{} ({}) --> {} ({})".format(
             self.input.get_simple_name(invalid_result="Unknown node"),

aiida/backends/sqlalchemy/migrations/versions/5a49629f0d45_dblink_indices.py

@@ -0,0 +1,30 @@
+"""Adding indices on the `input_id`, `output_id` and `type` column of the `DbLink` table
+
+Revision ID: 5a49629f0d45
+Revises: 5ddd24e52864
+Create Date: 2019-03-04 16:38:42.249231
+
+"""
+# pylint: disable=invalid-name,no-member,import-error,no-name-in-module
+from __future__ import absolute_import
+from alembic import op
+
+# revision identifiers, used by Alembic.
+revision = '5a49629f0d45'
+down_revision = '5ddd24e52864'
+branch_labels = None
+depends_on = None
+
+
+def upgrade():
+    """Migrations for the upgrade."""
+    op.create_index(op.f('ix_db_dblink_input_id'), 'db_dblink', ['input_id'], unique=False)
+    op.create_index(op.f('ix_db_dblink_output_id'), 'db_dblink', ['output_id'], unique=False)
+    op.create_index(op.f('ix_db_dblink_type'), 'db_dblink', ['type'], unique=False)
+
+
+def downgrade():
+    """Migrations for the downgrade."""
+    op.drop_index(op.f('ix_db_dblink_type'), table_name='db_dblink')
+    op.drop_index(op.f('ix_db_dblink_output_id'), table_name='db_dblink')
+    op.drop_index(op.f('ix_db_dblink_input_id'), table_name='db_dblink')

aiida/backends/sqlalchemy/models/node.py

@@ -244,7 +244,8 @@ class DbLink(Base):
     id = Column(Integer, primary_key=True)
     input_id = Column(
         Integer,
-        ForeignKey('db_dbnode.id', deferrable=True, initially="DEFERRED")
+        ForeignKey('db_dbnode.id', deferrable=True, initially="DEFERRED"),
+        index=True
     )
     output_id = Column(
         Integer,
@@ -253,14 +254,15 @@ class DbLink(Base):
             ondelete="CASCADE",
             deferrable=True,
             initially="DEFERRED"
-        )
+        ),
+        index=True
     )
 
     input = relationship("DbNode", primaryjoin="DbLink.input_id == DbNode.id")
     output = relationship("DbNode", primaryjoin="DbLink.output_id == DbNode.id")
 
     label = Column(String(255), index=True, nullable=False)
-    type = Column(String(255))
+    type = Column(String(255), index=True)
 
     # A calculation can have both a 'return' and a 'create' link to
     # a single data output node, which would violate the unique constraint