Extract QueryExecutor to eliminate duplication (#182)

Create new QueryExecutor class to encapsulate the pattern of executing
database queries and mapping results to domain objects.

Author: teoljungberg

CHANGELOG.md

@@ -20,6 +20,7 @@ changelog, see the [commits] for each version via the version links.
   all schemas (#177)
 - Drop Rails 7.1 due to EOL (#176)
 - YARD documentation improvements (#179)
+- Extract `QueryExecutor` to remove duplication (#182)
 
 ## [0.9.0]
 

lib/fx/adapters/postgres/functions.rb

@@ -1,4 +1,5 @@
 require "fx/function"
+require "fx/adapters/postgres/query_executor"
 
 module Fx
   module Adapters
@@ -28,31 +29,12 @@ class Functions
         # Wraps #all as a static facade.
         #
         # @return [Array<Fx::Function>]
-        def self.all(...)
-          new(...).all
-        end
-
-        def initialize(connection)
-          @connection = connection
-        end
-
-        # All of the functions that this connection has defined.
-        #
-        # @return [Array<Fx::Function>]
-        def all
-          functions_from_postgres.map { |function| to_fx_function(function) }
-        end
-
-        private
-
-        attr_reader :connection
-
-        def functions_from_postgres
-          connection.execute(FUNCTIONS_WITH_DEFINITIONS_QUERY)
-        end
-
-        def to_fx_function(result)
-          Fx::Function.new(result)
+        def self.all(connection)
+          QueryExecutor.call(
+            connection: connection,
+            query: FUNCTIONS_WITH_DEFINITIONS_QUERY,
+            model_class: Fx::Function
+          )
         end
       end
     end

lib/fx/adapters/postgres/query_executor.rb

@@ -0,0 +1,34 @@
+module Fx
+  module Adapters
+    class Postgres
+      # Executes database queries and maps results to domain objects.
+      # @api private
+      class QueryExecutor
+        def self.call(...)
+          new(...).call
+        end
+
+        def initialize(connection:, query:, model_class:)
+          @connection = connection
+          @query = query
+          @model_class = model_class
+        end
+
+        # Executes the query and maps results to domain objects.
+        #
+        # @return [Array] Array of domain objects (Functions or Triggers)
+        def call
+          results_from_postgres.map { |result| model_class.new(result) }
+        end
+
+        private
+
+        attr_reader :connection, :query, :model_class
+
+        def results_from_postgres
+          connection.execute(query)
+        end
+      end
+    end
+  end
+end

lib/fx/adapters/postgres/triggers.rb

@@ -1,4 +1,5 @@
 require "fx/trigger"
+require "fx/adapters/postgres/query_executor"
 
 module Fx
   module Adapters
@@ -28,31 +29,12 @@ class Triggers
         # Wraps #all as a static facade.
         #
         # @return [Array<Fx::Trigger>]
-        def self.all(...)
-          new(...).all
-        end
-
-        def initialize(connection)
-          @connection = connection
-        end
-
-        # All of the triggers that this connection has defined.
-        #
-        # @return [Array<Fx::Trigger>]
-        def all
-          triggers_from_postgres.map { |trigger| to_fx_trigger(trigger) }
-        end
-
-        private
-
-        attr_reader :connection
-
-        def triggers_from_postgres
-          connection.execute(TRIGGERS_WITH_DEFINITIONS_QUERY)
-        end
-
-        def to_fx_trigger(result)
-          Fx::Trigger.new(result)
+        def self.all(connection)
+          QueryExecutor.call(
+            connection: connection,
+            query: TRIGGERS_WITH_DEFINITIONS_QUERY,
+            model_class: Fx::Trigger
+          )
         end
       end
     end

spec/fx/adapters/postgres/functions_spec.rb

@@ -13,7 +13,7 @@
         $$ LANGUAGE plpgsql;
       SQL
 
-      functions = Fx::Adapters::Postgres::Functions.new(connection).all
+      functions = Fx::Adapters::Postgres::Functions.all(connection)
 
       first = functions.first
       expect(functions.size).to eq(1)
@@ -32,7 +32,7 @@
       connection.execute "CREATE SCHEMA IF NOT EXISTS other;"
       connection.execute "SET search_path = 'other';"
 
-      functions = Fx::Adapters::Postgres::Functions.new(connection).all
+      functions = Fx::Adapters::Postgres::Functions.all(connection)
 
       expect(functions).to be_empty
     end

spec/fx/adapters/postgres/query_executor_spec.rb

@@ -0,0 +1,75 @@
+require "spec_helper"
+
+RSpec.describe Fx::Adapters::Postgres::QueryExecutor, :db do
+  it "executes the query and maps results to objects" do
+    connection = ActiveRecord::Base.connection
+    query = "SELECT 'Hello World' as message, 'english' as language"
+    greeter = Class.new do
+      attr_reader :message, :language
+
+      def initialize(row)
+        @message = row.fetch("message")
+        @language = row.fetch("language")
+      end
+    end
+
+    results = described_class.call(
+      connection: connection,
+      query: query,
+      model_class: greeter
+    )
+
+    expect(results.size).to eq(1)
+    expect(results.first).to be_a(greeter)
+    expect(results.first.message).to eq("Hello World")
+    expect(results.first.language).to eq("english")
+  end
+
+  it "executes query with multiple results" do
+    connection = ActiveRecord::Base.connection
+    query = <<~SQL
+      SELECT 'first' as name
+      UNION ALL
+      SELECT 'second' as name
+      ORDER BY name
+    SQL
+    simple_name = Class.new do
+      attr_reader :name
+
+      def initialize(row)
+        @name = row.fetch("name")
+      end
+    end
+
+    results = described_class.call(
+      connection: connection,
+      query: query,
+      model_class: simple_name
+    )
+
+    expect(results.size).to eq(2)
+    expect(results).to all(be_a(simple_name))
+    expect(results.first.name).to eq("first")
+    expect(results.last.name).to eq("second")
+  end
+
+  it "returns an empty array when query returns no results" do
+    connection = ActiveRecord::Base.connection
+    query = "SELECT 'test' as name WHERE 1 = 0"
+    simple_name = Class.new do
+      attr_reader :name
+
+      def initialize(row)
+        @name = row.fetch("name")
+      end
+    end
+
+    results = described_class.call(
+      connection: connection,
+      query: query,
+      model_class: simple_name
+    )
+
+    expect(results).to eq([])
+  end
+end

spec/fx/adapters/postgres/triggers_spec.rb

@@ -27,7 +27,7 @@
             EXECUTE FUNCTION uppercase_users_name();
       SQL
 
-      triggers = Fx::Adapters::Postgres::Triggers.new(connection).all
+      triggers = Fx::Adapters::Postgres::Triggers.all(connection)
 
       first = triggers.first
       expect(triggers.size).to eq(1)
@@ -40,7 +40,7 @@
       connection.execute "CREATE SCHEMA IF NOT EXISTS other;"
       connection.execute "SET search_path = 'other';"
 
-      triggers = Fx::Adapters::Postgres::Triggers.new(connection).all
+      triggers = Fx::Adapters::Postgres::Triggers.all(connection)
 
       expect(triggers).to be_empty
     end