Initial suggestion

Author: morten.lund@maskon.no

lib/data_layer.ex

@@ -252,6 +252,31 @@ defmodule AshPostgres.DataLayer do
     ]
   }
 
+  @partitioning %Spark.Dsl.Section{
+    name: :partitioning,
+    describe: """
+    A section for configuring the initial partitioning of the table
+    """,
+    examples: [
+      """
+      partitioning do
+        method :list
+        attribute :post
+      end
+      """
+    ],
+    schema: [
+      method: [
+        type: {:one_of, [:range, :list, :hash]},
+        doc: "Specifying what partitioning method to use"
+      ],
+      attribute: [
+        type: :atom,
+        doc: "The attribute to partition on"
+      ]
+    ]
+  }
+
   @postgres %Spark.Dsl.Section{
     name: :postgres,
     describe: """
@@ -262,7 +287,8 @@ defmodule AshPostgres.DataLayer do
       @custom_statements,
       @manage_tenant,
       @references,
-      @check_constraints
+      @check_constraints,
+      @partitioning
     ],
     modules: [
       :repo

lib/data_layer/info.ex

@@ -222,4 +222,14 @@ defmodule AshPostgres.DataLayer.Info do
   def manage_tenant_update?(resource) do
     Extension.get_opt(resource, [:postgres, :manage_tenant], :update?, false)
   end
+
+  @doc "Partitioning method"
+  def partitioning_method(resource) do
+    Extension.get_opt(resource, [:postgres, :partitioning], :method, nil)
+  end
+
+  @doc "Partitioning attribute"
+  def partitioning_attribute(resource) do
+    Extension.get_opt(resource, [:postgres, :partitioning], :attribute, nil)
+  end
 end

lib/migration_generator/migration_generator.ex

@@ -1192,14 +1192,25 @@ defmodule AshPostgres.MigrationGenerator do
 
   defp group_into_phases(
          [
-           %Operation.CreateTable{table: table, schema: schema, multitenancy: multitenancy} | rest
+           %Operation.CreateTable{
+             table: table,
+             schema: schema,
+             multitenancy: multitenancy,
+             partitioning: partitioning
+           }
+           | rest
          ],
          nil,
          acc
        ) do
     group_into_phases(
       rest,
-      %Phase.Create{table: table, schema: schema, multitenancy: multitenancy},
+      %Phase.Create{
+        table: table,
+        schema: schema,
+        multitenancy: multitenancy,
+        partitioning: partitioning
+      },
       acc
     )
   end
@@ -1801,7 +1812,8 @@ defmodule AshPostgres.MigrationGenerator do
         table: snapshot.table,
         schema: snapshot.schema,
         multitenancy: snapshot.multitenancy,
-        old_multitenancy: empty_snapshot.multitenancy
+        old_multitenancy: empty_snapshot.multitenancy,
+        partitioning: snapshot.partitioning
       }
       | acc
     ])
@@ -2836,7 +2848,8 @@ defmodule AshPostgres.MigrationGenerator do
       repo: AshPostgres.DataLayer.Info.repo(resource, :mutate),
       multitenancy: multitenancy(resource),
       base_filter: AshPostgres.DataLayer.Info.base_filter_sql(resource),
-      has_create_action: has_create_action?(resource)
+      has_create_action: has_create_action?(resource),
+      partitioning: partitioning(resource)
     }
 
     hash =
@@ -2911,6 +2924,20 @@ defmodule AshPostgres.MigrationGenerator do
     end)
   end
 
+  defp partitioning(resource) do
+    method = AshPostgres.DataLayer.Info.partitioning_method(resource)
+    attribute = AshPostgres.DataLayer.Info.partitioning_attribute(resource)
+
+    if not is_nil(method) and not is_nil(attribute) do
+      %{
+        method: method,
+        attribute: attribute
+      }
+    else
+      nil
+    end
+  end
+
   defp multitenancy(resource) do
     strategy = Ash.Resource.Info.multitenancy_strategy(resource)
     attribute = Ash.Resource.Info.multitenancy_attribute(resource)

lib/migration_generator/operation.ex

@@ -131,7 +131,7 @@ defmodule AshPostgres.MigrationGenerator.Operation do
 
   defmodule CreateTable do
     @moduledoc false
-    defstruct [:table, :schema, :multitenancy, :old_multitenancy]
+    defstruct [:table, :schema, :multitenancy, :old_multitenancy, :partitioning]
   end
 
   defmodule AddAttribute do

lib/migration_generator/phase.ex

@@ -3,24 +3,21 @@ defmodule AshPostgres.MigrationGenerator.Phase do
 
   defmodule Create do
     @moduledoc false
-    defstruct [:table, :schema, :multitenancy, operations: [], commented?: false]
+    defstruct [:table, :schema, :multitenancy, partitioning: nil, operations: [], commented?: false]
 
     import AshPostgres.MigrationGenerator.Operation.Helper, only: [as_atom: 1]
 
-    def up(%{schema: schema, table: table, operations: operations, multitenancy: multitenancy}) do
+    def up(%{schema: schema, table: table, operations: operations, multitenancy: multitenancy, partitioning: partitioning}) do
       if multitenancy.strategy == :context do
-        "create table(:#{as_atom(table)}, primary_key: false, prefix: prefix()) do\n" <>
+        arguments = arguments([prefix("prefix()"), options(partitioning: partitioning)])
+
+        "create table(:#{as_atom(table)}, primary_key: false#{arguments}) do\n" <>
           Enum.map_join(operations, "\n", fn operation -> operation.__struct__.up(operation) end) <>
           "\nend"
       else
-        opts =
-          if schema do
-            ", prefix: \"#{schema}\""
-          else
-            ""
-          end
+        arguments = arguments([prefix(schema), options(partitioning: partitioning)])
 
-        "create table(:#{as_atom(table)}, primary_key: false#{opts}) do\n" <>
+        "create table(:#{as_atom(table)}, primary_key: false#{arguments}) do\n" <>
           Enum.map_join(operations, "\n", fn operation -> operation.__struct__.up(operation) end) <>
           "\nend"
       end
@@ -40,6 +37,27 @@ defmodule AshPostgres.MigrationGenerator.Phase do
         "drop table(:#{as_atom(table)}#{opts})"
       end
     end
+
+    def arguments(["",""]), do: ""
+    def arguments(arguments), do: ", " <> Enum.join(Enum.reject(arguments, &is_nil(&1)), ",")
+
+    def prefix(nil), do: nil
+    def prefix(schema), do: "prefix: #{schema}"
+
+    def options(_options, _acc \\ [])
+    def options([], []), do: ""
+    def options([], acc), do: "options: \"#{Enum.join(acc, " ")}\""
+
+    def options([{:partitioning, %{method: method, attribute: attribute}} | rest], acc) do
+      option = "PARTITION BY #{String.upcase(Atom.to_string(method))} (#{attribute})"
+
+      rest
+      |> options(acc ++ [option])
+    end
+
+    def options([_| rest], acc) do
+      options(rest, acc)
+    end
   end
 
   defmodule Alter do

lib/partitioning.ex

@@ -0,0 +1,79 @@
+defmodule AshPostgres.Partitioning do
+  @moduledoc false
+
+  @doc """
+  Create a new partition for a resource
+  """
+  def create_partition(resource, opts) do
+    repo = AshPostgres.DataLayer.Info.repo(resource)
+
+    resource
+    |> AshPostgres.DataLayer.Info.partitioning_method()
+    |> case do
+      :range ->
+        create_range_partition(repo, resource, opts)
+
+      :list ->
+        create_list_partition(repo, resource, opts)
+
+      :hash ->
+        create_hash_partition(repo, resource, opts)
+
+      unsupported_method ->
+        raise "Invalid partition method, got: #{unsupported_method}"
+    end
+  end
+
+  @doc """
+  Check if partition exists
+  """
+  def exists?(resource, opts) do
+    repo = AshPostgres.DataLayer.Info.repo(resource)
+    key = Keyword.fetch!(opts, :key)
+    table = AshPostgres.DataLayer.Info.table(resource)
+    partition_name = table <> "_" <> "#{key}"
+
+    partition_exists?(repo, resource, partition_name)
+  end
+
+  # TBI
+  defp create_range_partition(repo, resource, opts) do
+  end
+
+  defp create_list_partition(repo, resource, opts) do
+    key = Keyword.fetch!(opts, :key)
+    table = AshPostgres.DataLayer.Info.table(resource)
+    partition_name = table <> "_" <> "#{key}"
+
+    if partition_exists?(repo, resource, partition_name) do
+      {:error, :allready_exists}
+    else
+      Ecto.Adapters.SQL.query(
+        repo,
+        "CREATE TABLE #{partition_name} PARTITION OF public.#{table} FOR VALUES IN (#{key})"
+      )
+
+      if partition_exists?(repo, resource, partition_name) do
+        :ok
+      else
+        {:error, "Unable to create partition"}
+      end
+    end
+  end
+
+  # TBI
+  defp create_hash_partition(repo, resource, opts) do
+  end
+
+  defp partition_exists?(repo, resource, parition_name) do
+    %Postgrex.Result{} =
+      result =
+      repo
+      |> Ecto.Adapters.SQL.query!(
+        "select table_name from information_schema.tables t where t.table_schema = 'public' and t.table_name = $1",
+        [parition_name]
+      )
+
+    result.num_rows > 0
+  end
+end

priv/resource_snapshots/test_repo/partitioned_posts/20250214114101.json

@@ -0,0 +1,43 @@
+{
+  "attributes": [
+    {
+      "allow_nil?": false,
+      "default": "fragment(\"gen_random_uuid()\")",
+      "generated?": false,
+      "primary_key?": true,
+      "references": null,
+      "size": null,
+      "source": "id",
+      "type": "uuid"
+    },
+    {
+      "allow_nil?": false,
+      "default": "1",
+      "generated?": false,
+      "primary_key?": true,
+      "references": null,
+      "size": null,
+      "source": "key",
+      "type": "bigint"
+    }
+  ],
+  "base_filter": null,
+  "check_constraints": [],
+  "custom_indexes": [],
+  "custom_statements": [],
+  "has_create_action": false,
+  "hash": "7FE5D9659135887A47FAE2729CEB0281FA8FF392EDB3B43426EAFD89A1518FEB",
+  "identities": [],
+  "multitenancy": {
+    "attribute": null,
+    "global": null,
+    "strategy": null
+  },
+  "partitioning": {
+    "attribute": "key",
+    "method": "list"
+  },
+  "repo": "Elixir.AshPostgres.TestRepo",
+  "schema": null,
+  "table": "partitioned_posts"
+}

priv/test_repo/migrations/20250214114101_partitioned_post.exs

@@ -0,0 +1,20 @@
+defmodule AshPostgres.TestRepo.Migrations.PartitionedPost do
+  @moduledoc """
+  Updates resources based on their most recent snapshots.
+
+  This file was autogenerated with `mix ash_postgres.generate_migrations`
+  """
+
+  use Ecto.Migration
+
+  def up do
+    create table(:partitioned_posts, primary_key: false, options: "PARTITION BY LIST (key)") do
+      add(:id, :uuid, null: false, default: fragment("gen_random_uuid()"), primary_key: true)
+      add(:key, :bigint, null: false, default: 1, primary_key: true)
+    end
+  end
+
+  def down do
+    drop(table(:partitioned_posts))
+  end
+end

test/migration_generator_test.exs

@@ -304,6 +304,56 @@ defmodule AshPostgres.MigrationGeneratorTest do
     end
   end
 
+  describe "creating initial snapshots for resources with partitioning" do
+    setup do
+      on_exit(fn ->
+        File.rm_rf!("test_snapshots_path")
+        File.rm_rf!("test_migration_path")
+      end)
+
+      defposts do
+        postgres do
+          partitioning do
+            method(:list)
+            attribute(:title)
+          end
+        end
+
+        attributes do
+          uuid_primary_key(:id)
+          attribute(:title, :string, public?: true)
+        end
+      end
+
+      defdomain([Post])
+
+      AshPostgres.MigrationGenerator.generate(Domain,
+        snapshot_path: "test_snapshots_path",
+        migration_path: "test_migration_path",
+        quiet: false,
+        format: false
+      )
+
+      :ok
+    end
+
+    test "the migration sets up resources correctly" do
+      # the snapshot exists and contains valid json
+      assert File.read!(Path.wildcard("test_snapshots_path/test_repo/posts/*.json"))
+             |> Jason.decode!(keys: :atoms!)
+
+      assert [file] =
+               Path.wildcard("test_migration_path/**/*_migrate_resources*.exs")
+               |> Enum.reject(&String.contains?(&1, "extensions"))
+
+      file_contents = File.read!(file)
+
+      # the migration creates the table with options specifing how to partition the table
+      assert file_contents =~
+               ~S{create table(:posts, primary_key: false, options: "PARTITION BY LIST (title)") do}
+    end
+  end
+
   describe "custom_indexes with `concurrently: true`" do
     setup do
       on_exit(fn ->