feat: add pk information in x-electric-schema header (#235)

Addresses #229

.changeset/nasty-birds-tease.md

@@ -0,0 +1,6 @@
+---
+"@core/sync-service": patch
+---
+
+Add PK index of column is part of the PK in the column information that is part of the schema information returned in the x-electric-schema 
+HTTP header.

packages/sync-service/lib/electric/schema.ex

@@ -8,6 +8,7 @@ defmodule Electric.Schema do
   @type schema :: %{
           :type => type_name(),
           optional(:dims) => non_neg_integer(),
+          optional(:pk_index) => non_neg_integer(),
           optional(:max_length) => String.t(),
           optional(:length) => String.t(),
           optional(:precision) => String.t(),
@@ -49,6 +50,7 @@ defmodule Electric.Schema do
   defp schema(col_info) do
     %{type: type(col_info)}
     |> add_dims(col_info)
+    |> add_pk(col_info)
     |> add_modifier(col_info)
   end
 
@@ -61,6 +63,12 @@ defmodule Electric.Schema do
     Map.put(schema, :dims, array_dimensions)
   end
 
+  defp add_pk(schema, %{pk_position: nil}), do: schema
+
+  defp add_pk(schema, %{pk_position: idx}) do
+    Map.put(schema, :pk_index, idx)
+  end
+
   defp add_modifier(%{type: type} = schema, %{type_mod: type_mod})
        when type_mod > 0 and type in @variable_length_character_types do
     Map.put(schema, :max_length, type_mod - 4)

packages/sync-service/test/electric/plug/serve_shape_plug_test.exs

@@ -190,7 +190,7 @@ defmodule Electric.Plug.ServeShapePlugTest do
         |> ServeShapePlug.call([])
 
       assert Plug.Conn.get_resp_header(conn, "x-electric-schema") == [
-               ~s|{"id":{"type":"int8"}}|
+               ~s|{"id":{"type":"int8","pk_index":0}}|
              ]
     end
 

packages/sync-service/test/electric/schema_test.exs

@@ -495,5 +495,29 @@ defmodule Electric.SchemaTest do
         assert schema == unquote(Macro.escape(expected_schema))
       end
     end
+
+    test "returns the correct schema for a table with a composite primary key", %{db_conn: conn} do
+      Postgrex.query!(
+        conn,
+        """
+        CREATE TABLE items (
+          i INTEGER,
+          name VARCHAR,
+          value BOOLEAN,
+          PRIMARY KEY (i, value)
+        )
+        """,
+        []
+      )
+
+      {:ok, column_info} = DirectInspector.load_column_info({"public", "items"}, conn)
+
+      %{"i" => i_schema, "name" => name_schema, "value" => value_schema} =
+        Schema.from_column_info(column_info)
+
+      assert i_schema == %{type: "int4", pk_index: 0}
+      assert name_schema == %{type: "varchar"}
+      assert value_schema == %{type: "bool", pk_index: 1}
+    end
   end
 end