Make source repo unique by project

We add a unique constraint on source_repo table to prevent multiple
links of the same remote repository to a given project.

The UI already prevents duplicates (from ef585b6e) but it seems better
to enforce this in the database model.

hubsrht/alembic/versions/9deca12b2917_make_source_repo_unique_by_project.py

@@ -0,0 +1,32 @@
+"""Make source repo unique by project
+
+Revision ID: 9deca12b2917
+Revises: 4da86bb54214
+Create Date: 2020-12-27 15:10:57.823055
+
+"""
+
+# revision identifiers, used by Alembic.
+revision = '9deca12b2917'
+down_revision = '4da86bb54214'
+
+from alembic import op
+
+
+def upgrade():
+    # Drop duplicate source_repo keeping the latest.
+    op.execute(
+        "DELETE FROM source_repo A"
+        " USING source_repo B"
+        " WHERE A.project_id = B.project_id AND A.remote_id = B.remote_id"
+        " AND A.repo_type = B.repo_type AND A.id < B.id;"
+    )
+    op.create_unique_constraint(
+        "project_source_repo_unique",
+        "source_repo",
+        ["project_id", "remote_id", "repo_type"],
+    )
+
+
+def downgrade():
+    op.drop_constraint("project_source_repo_unique", "source_repo", type_="unique")

hubsrht/types/sourcerepo.py

@@ -14,6 +14,12 @@ class RepoType(Enum):
 
 class SourceRepo(Base):
     __tablename__ = "source_repo"
+    __table_args__ = (
+        sa.UniqueConstraint(
+            "project_id", "remote_id", "repo_type",
+            name="project_source_repo_unique",
+        ),
+    )
     id = sa.Column(sa.Integer, primary_key=True)
     remote_id = sa.Column(sa.Integer, nullable=False)
     created = sa.Column(sa.DateTime, nullable=False)