Add check for duplicate memberships

amanuensis/backend/membership.py

@@ -2,6 +2,8 @@
 Membership query interface
 """
 
+from sqlalchemy import select, func
+
 from amanuensis.db import DbContext, Membership
 from amanuensis.errors import ArgumentError
 
@@ -14,7 +16,7 @@ def create(
     """
     Create a new user membership in a lexicon.
     """
-    # Quick argument verification
+    # Verify argument types are correct
     if not isinstance(user_id, int):
         raise ArgumentError('user_id')
     if not isinstance(lexicon_id, int):
@@ -22,6 +24,14 @@ def create(
     if not isinstance(is_editor, bool):
         raise ArgumentError('is_editor')
 
+    # Verify user has not already joined lexicon
+    if db(
+        select(func.count(Membership.id))
+        .where(Membership.user_id == user_id)
+        .where(Membership.lexicon_id == lexicon_id)
+    ).scalar() > 0:
+        raise ArgumentError('User is already a member of lexicon')
+
     new_membership = Membership(
         user_id=user_id,
         lexicon_id=lexicon_id,

amanuensis/db/models.py

@@ -2,6 +2,8 @@
 Data model SQL definitions
 """
 import enum
+import uuid
+
 from sqlalchemy import (
     Boolean,
     Column,
@@ -17,7 +19,7 @@ from sqlalchemy import (
     TypeDecorator,
 )
 from sqlalchemy.orm import relationship, backref
-import uuid
+from sqlalchemy.sql.schema import UniqueConstraint
 
 from .database import ModelBase
 
@@ -233,6 +235,9 @@ class Membership(ModelBase):
     Represents a user's participation in a Lexicon game.
     """
     __tablename__ = 'membership'
+    __table_args__ = (
+        UniqueConstraint('user_id', 'lexicon_id'),
+    )
 
     ###################
     # Membership keys #

tests/test_membership.py

@@ -1,4 +1,9 @@
-from amanuensis.db import DbContext
+import pytest
+
+from sqlalchemy import select
+
+from amanuensis.db import *
+from amanuensis.errors import ArgumentError
 import amanuensis.backend.membership as memq
 
 
@@ -15,10 +20,22 @@ def test_create_membership(db: DbContext, make_user, make_lexicon):
     assert mem, 'Failed to create membership'
 
     # Check that the user and lexicon are mutually visible in the ORM relationships
-    assert new_user.memberships, 'User memberships not updated'
+    assert any(map(lambda mem: mem.lexicon == new_lexicon, new_user.memberships))
-    assert new_lexicon.memberships, 'Lexicon memberships not updated'
+    assert any(map(lambda mem: mem.user == new_user, new_lexicon.memberships))
-    assert new_user.memberships[0].lexicon_id == new_lexicon.id
-    assert new_lexicon.memberships[0].user_id == new_user.id
 
     # Check that the editor flag was set properly
-    assert new_lexicon.memberships
+    editor = db(
+        select(User)
+        .join(User.memberships)
+        .join(Membership.lexicon)
+        .where(Lexicon.id == new_lexicon.id)
+        .where(Membership.is_editor == True)
+    ).scalar_one()
+    assert editor is not None
+    assert isinstance(editor, User)
+    assert editor.id == new_user.id
+
+    # Check that joining twice is not allowed
+    with pytest.raises(ArgumentError):
+        mem2 = memq.create(db, new_user.id, new_lexicon.id, False)
+        assert mem2