feat(db): replace deferred unique constraints with partial unique indexes for LLM model configs

Replace deferred UniqueConstraints with partial unique indexes for user and group default configurations in the LLM model configs table. This change improves performance and ensures at most one default config per user/group while maintaining data integrity. The migration script has been updated accordingly to create and drop the new indexes.

gns3server/db_migrations/versions/20260303_create_llm_model_configs_table.py

@@ -54,18 +54,6 @@ def upgrade() -> None:
             "model_type IN ('text', 'vision', 'stt', 'tts', 'multimodal', 'embedding', 'reranking', 'other')",
             name='valid_model_type_check'
         ),
-        sa.UniqueConstraint(
-            'user_id', 'is_default',
-            name='unique_user_default',
-            deferrable=True, initially='deferred',
-            postgresql_where=sa.text("is_default = TRUE AND user_id IS NOT NULL")
-        ),
-        sa.UniqueConstraint(
-            'group_id', 'is_default',
-            name='unique_group_default',
-            deferrable=True, initially='deferred',
-            postgresql_where=sa.text("is_default = TRUE AND group_id IS NOT NULL")
-        ),
     )
 
     # Create indexes for efficient queries
@@ -74,6 +62,20 @@ def upgrade() -> None:
     op.create_index('idx_llm_model_configs_model_type', 'llm_model_configs', ['model_type'])
     op.create_index('idx_llm_model_configs_config', 'llm_model_configs', ['config'], postgresql_using='gin')
 
+    # Create partial unique indexes for default configs
+    # Each user can have at most one default config
+    op.execute("""
+        CREATE UNIQUE INDEX unique_user_default
+        ON llm_model_configs (user_id)
+        WHERE is_default = TRUE AND user_id IS NOT NULL
+    """)
+    # Each group can have at most one default config
+    op.execute("""
+        CREATE UNIQUE INDEX unique_group_default
+        ON llm_model_configs (group_id)
+        WHERE is_default = TRUE AND group_id IS NOT NULL
+    """)
+
 
 def downgrade() -> None:
     # Drop indexes
@@ -81,6 +83,8 @@ def downgrade() -> None:
     op.drop_index('idx_llm_model_configs_model_type', table_name='llm_model_configs')
     op.drop_index('idx_llm_model_configs_group_id', table_name='llm_model_configs')
     op.drop_index('idx_llm_model_configs_user_id', table_name='llm_model_configs')
+    op.drop_index('unique_user_default', table_name='llm_model_configs')
+    op.drop_index('unique_group_default', table_name='llm_model_configs')
 
     # Drop table
     op.drop_table('llm_model_configs')