Fetch many identities, returning a mapping from identities to results.
Fetch many identities, returning a mapping from identities to results. If an identity wasn't found won't appear in the keys.
Fetch one identity, returning a None if it wasn't found.
The name of the data source.
Use fetchOne for implementing of fetchMany.
Use fetchOne for implementing of fetchMany. Use only when the data
source doesn't support batching.
Derive a DataSourceIdentity from an identity, suitable for storing the result
of such identity in a DataSourceCache.
A
DataSourceis the recipe for fetching a certain identityI, which yields results of typeA.