Feast is inconsistent in how it uses entity names (as defined in Feast) vs entity join keys (i.e. the original column name in the offline store). It leads to several issues:

• get_online_features doesn't work properly when the user uses entity aliases (see below for example in historical retrieval)
• get_online_features callers need to find what the entity name is since it doesn't naturally reflect the join key they have on hand.

Expected behavior

get_online_features should take join keys instead of entity names (and understand with_join_key_map)

Background

See also a similar discussion in Entity name/joinkey dichotomy

Historical feature retrieval

In get_historical_features: entity join keys (aka the column in the original table) are expected.

When there are multiple possible join keys that refer to the same entity, we require the use of with_join_key_map (code) on the feature view. Then get_historical_features takes in the join keys directly.

Example: for a given shopping transaction, get user features for both buyers + sellers

    transaction_service = FeatureService(
            name="transactions",
            features=[
                user_feature_view
                    .with_name("buyer_features")
                    .with_join_key_map(
                        {"user_id": "buyer_id"}
                    ),
                user_feature_view
                    .with_name("seller_features")
                    .with_join_key_map(
                        {"user_id": "seller_id"}
                    ),
            ])

     feature_store.get_historical_features(
         features=transaction_service, 
         entity_df=pd.DataFrame.from_dict(
                {
                    "buyer_id": [1001, 1002],
                    "seller_id": [1003, 1003],
                    "event_timestamp": [
                        datetime(2021, 4, 12, 10, 59, 42),
                        datetime(2021, 4, 12, 8, 12, 10),
                    ],
                }
            )
     )

Online feature retrieval

In get_online_features, entity names are expected.

Feature / entity definitions in the feature repo

In defining Feast objects, Feast FeatureView objects use entity names.