An Ash data layer for ScyllaDB using Xandra (direct CQL driver).

This data layer implements the Ash.DataLayer behaviour to allow Ash resources to be backed by ScyllaDB/Cassandra.

Configuration

Configure your resource to use this data layer:

defmodule MyApp.MyResource do
  use Ash.Resource,
    data_layer: AshScylla.DataLayer

  attributes do
    uuid_primary_key :id
    attribute :name, :string
  end

  relationships do
    # Define relationships as needed
  end
end

Features Supported

• :create - Create records
• :read - Read records with filtering
• :update - Update records
• :destroy - Delete records
• :filter - Filter queries
• :limit - Limit results
• :select - Select specific fields
• :multitenancy - Keyspace-based multitenancy
• :upsert - Upsert records (INSERT IF NOT EXISTS with LWT)
• :update_query - Bulk update via filtered queries
• :destroy_query - Bulk delete via filtered queries
• :keyset - Token-based keyset pagination (the default pagination mode)
• :distinct - DISTINCT on partition key columns
• {:aggregate, :count} - Per-partition COUNT aggregates
• {:atomic, :update} - Atomic updates via LWT (IF clauses)
• {:atomic, :upsert} - Atomic upserts via LWT
• :boolean_filter - OR filter rewriting to IN where possible

Limitations

Since ScyllaDB/Cassandra is a wide-column store, not all SQL features are supported:

• No JOINs (use denormalization or multiple queries)
• Expression calculations are done in Elixir post-processing (not in-database)
• DISTINCT only works on partition key columns
• Limited aggregation support
• Combination queries (UNION/INTERSECT) are not supported
• No transactions across partitions (lightweight transactions only)
• Locking is a no-op (use LWT for conditional operations)
• No complex WHERE clauses on non-primary key columns without secondary indexes
• Cross-partition aggregates require materialized views
• CQL ORDER BY only works on clustering columns within a partition