add TemplateFolder model

a TemplateFolder has a service, a name, and a parent. Parent is a
nullable foreign key pointing to another TemplateFolder instance. We
don't do any checks here for cyclical or otherwise invalid folder
structures so keep your data clean, folks!

Unsurprisingly, a Template can be part of a TemplateFolder - there's a
mapping class (template_folder_map to avoid giving it a dumb name) -
this mapping table shouldn't be interacted with directly - rather, you
should use the `Template.folder` or `TemplateFolder.templates`
relationship.

app/models.py

@@ -706,6 +706,27 @@ class TemplateProcessTypes(db.Model):
     name = db.Column(db.String(255), primary_key=True)
 
 
+class TemplateFolder(db.Model):
+    __tablename__ = 'template_folder'
+
+    id = db.Column(UUID(as_uuid=True), primary_key=True, default=uuid.uuid4)
+    service_id = db.Column(UUID(as_uuid=True), db.ForeignKey('services.id'), nullable=False)
+    name = db.Column(db.String, nullable=False)
+    parent_id = db.Column(UUID(as_uuid=True), db.ForeignKey('template_folder.id'), nullable=True)
+
+    service = db.relationship('Service')
+    parent = db.relationship('TemplateFolder', remote_side=[id], backref='children')
+
+
+template_folder_map = db.Table(
+    'template_folder_map',
+    db.Model.metadata,
+    # template_id is a primary key as a template can only belong in one folder
+    db.Column('template_id', UUID(as_uuid=True), db.ForeignKey('templates.id'), primary_key=True, nullable=False),
+    db.Column('template_folder_id', UUID(as_uuid=True), db.ForeignKey('template_folder.id'), nullable=False),
+)
+
+
 PRECOMPILED_TEMPLATE_NAME = 'Pre-compiled PDF'
 
 
@@ -837,6 +858,13 @@ class Template(TemplateBase):
     service = db.relationship('Service', backref='templates')
     version = db.Column(db.Integer, default=0, nullable=False)
 
+    folder = db.relationship(
+        'TemplateFolder',
+        secondary=template_folder_map,
+        uselist=False,
+        backref=db.backref('templates', lazy='dynamic')
+    )
+
     def get_link(self):
         # TODO: use "/v2/" route once available
         return url_for(

migrations/versions/0242_template_folders.py

@@ -0,0 +1,39 @@
+"""
+
+Revision ID: 0242_template_folders
+Revises: 0241_another_letter_org
+Create Date: 2018-10-26 16:00:40.173840
+
+"""
+from alembic import op
+import sqlalchemy as sa
+from sqlalchemy.dialects import postgresql
+
+revision = '0242_template_folders'
+down_revision = '0241_another_letter_org'
+
+
+def upgrade():
+    # ### commands auto generated by Alembic - please adjust! ###
+    op.create_table('template_folder',
+        sa.Column('id', postgresql.UUID(as_uuid=True), nullable=False),
+        sa.Column('service_id', postgresql.UUID(as_uuid=True), nullable=False),
+        sa.Column('name', sa.String(), nullable=False),
+        sa.Column('parent_id', postgresql.UUID(as_uuid=True), nullable=True),
+        sa.ForeignKeyConstraint(['parent_id'], ['template_folder.id'], ),
+        sa.ForeignKeyConstraint(['service_id'], ['services.id'], ),
+        sa.PrimaryKeyConstraint('id')
+    )
+    op.create_table('template_folder_map',
+        sa.Column('template_id', postgresql.UUID(as_uuid=True), nullable=False),
+        sa.Column('template_folder_id', postgresql.UUID(as_uuid=True), nullable=False),
+        sa.ForeignKeyConstraint(['template_folder_id'], ['template_folder.id'], ),
+        sa.ForeignKeyConstraint(['template_id'], ['templates.id'], ),
+        sa.PrimaryKeyConstraint('template_id')
+    )
+
+
+def downgrade():
+    op.drop_table('template_folder_map')
+    op.drop_table('template_folder')
+    # ### end Alembic commands ###