An Ash data layer for ClickHouse.

This data layer implements the Ash.DataLayer behaviour so that Ash resources can be backed by a ClickHouse columnar OLAP database. It uses the clickhouse client under the hood.

Configuration

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

  clickhouse do
    table "my_table"
    repo MyApp.Repo
  end

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

Features Supported

• :create / :read / :update / :destroy
• :filter — full WHERE support
• :limit / :offset — ClickHouse supports both natively
• :select — column projection
• :sort — ORDER BY
• :distinct — SELECT DISTINCT
• :multitenancy — database- or attribute-based
• :bulk_create — batch INSERT
• :update_query / :destroy_query — ALTER TABLE ... UPDATE/DELETE
• :calculate — in-memory calculations
• :composite_primary_key
• :nested_expressions / :boolean_filter
• :async_engine
• :expression_calculation

• {:aggregate, :count | :sum | :avg | :min | :max} — native aggregates

• {:query_aggregate, :count | :sum | :avg | :min | :max}

• Combination queries (UNION/INTERSECT) — executed by Ash in memory

Relationship aggregates

attach_aggregates/5 supports {:aggregate, :count | :sum | :avg | :min | :max} over belongs_to, has_many, and has_one relationships. A belongs_to aggregate is a lookup of the related row's scalar field (e.g. customer.tier), not a true aggregation across multiple rows — ClickHouse's lack of JOINs makes this distinction more visible than in a Postgres-backed data layer. has_many/has_one aggregates are real grouped aggregations (e.g. "count of orders per customer"). Multi-hop relationship paths are not supported and fall back to each aggregate's default_value.

Features NOT Supported

• :transact — ClickHouse has no multi-statement transactions
• :lock — locking is a no-op
• :keyset — ClickHouse has no token-based keyset pagination
• :upsert — ClickHouse has no ON CONFLICT (use :create + :update_query)
• :expression_calculation_sort — not supported
• :aggregate_filter / :aggregate_sort — not supported
• :update_many — use :update_query
• :composite_type / :through_relationship
• :join — JOINs are not yet implemented
• :filter_relationship / {:exists, :unrelated} / {:aggregate_relationship, _}

• {:query_aggregate, :list | :first | :exists | :custom} — only count/sum/avg/min/max