Implement database adapters to be able to have diferent ways of implementing the same feature

Author: andresgutgon

.gitignore

@@ -6,5 +6,7 @@
 /doc/
 /pkg/
 /spec/reports/
+.ruby-version
+.byebug_history
 /tmp/
 .DS_STORE

README.md

@@ -142,6 +142,8 @@ ActiveReporting::Configuration.setting = value
 
 `metric_lookup_class` - The name of a constant used to lookup prebuilt `Reporting::Metric` objects by name. The constant should define a class method called `#lookup` which can take a string or symbol of the metric name. (Default: `::Metric`)
 
+`db_adapter` - Each database has a diferent way of doing the same thing on SQL. This is an abstraction layer on each database. For example `PostGreSQL` have a native `date_trunc` while `MySQL` doesn't so we do the same in another way. Make sure to chosse your database's adapter (Default: `:sqlite3`). If you want MySQL put `:mysql2` and if you want PostGreSQL put `:postgresql`.
+
 
 ## ActiveReporting::FactModel
 
@@ -219,7 +221,7 @@ class PhoneFactModel < ActiveReporting::FactModel
 end
 ```
 
-### Implicit hierarchies with datetime columns (PostgreSQL support only)
+### Implicit hierarchies with datetime columns (PostgreSQL and MySQL support only)
 
 The fastest approach to group by certain date metrics is to create so-called "date dimensions". For
 those Postgres users that are restricted from organizing their data in this way, Postgres provides
@@ -235,7 +237,6 @@ end
 
 When creating a metric, ActiveReporting will recognize implicit hierarchies for this dimension. The hierarchies correspond to the [values](https://www.postgresql.org/docs/8.1/static/functions-datetime.html#FUNCTIONS-DATETIME-TRUNC) supported by PostgreSQL. (See example under the metric section, below.)
 
-*NOTE*: PRs welcomed to support this functionality in other databases.
 
 ## Configuring Dimension Filters
 

lib/active_reporting.rb

@@ -1,6 +1,11 @@
 # frozen_string_literal: true
 
 require 'active_record'
+require 'active_reporting/database_adapters/base'
+require 'active_reporting/database_adapters/sqlite_adapter'
+require 'active_reporting/database_adapters/mysql_adapter'
+require 'active_reporting/database_adapters/postgresql_adapter'
+require 'active_reporting/database_adapters/factory'
 require 'active_reporting/active_record_adaptor'
 require 'active_reporting/configuration'
 require 'active_reporting/dimension'

lib/active_reporting/configuration.rb

@@ -13,6 +13,22 @@ def self.config
       yield self
     end
 
+    # Set database adapter. There are some SQL functions that are only
+    # available in some databases. You need to specify adapter
+    #
+    # Default db_adapter: SqliteAdapter
+    def self.db_adapter
+      @db_adapter ||= DatabaseAdapters::Factory.for_database(:sqlite3)
+    end
+
+    # Set database adapter. There are some SQL functions that are only
+    # available in some databases. You need to specify adapter
+    #
+    # @param [Symbol] adapter_name
+    def self.db_adapter=(adapter_name)
+      @db_adapter = DatabaseAdapters::Factory.for_database(adapter_name)
+    end
+
     # The default label used by all dimensions if not set otherwise
     #
     # Default value is `:name`
@@ -57,6 +73,7 @@ def self.ransack_fallback
     # @return [Boolean]
     def self.ransack_fallback=(fallback)
       raise RansackNotAvailable unless ransack_available
+
       @ransack_fallback = fallback
     end
 

lib/active_reporting/database_adapters/base.rb

@@ -0,0 +1,33 @@
+# frozen_string_literal: true
+
+module ActiveReporting
+  module DatabaseAdapters
+    DatabaseNotSupported = Class.new(StandardError)
+    MethodNotImplemented = Class.new(StandardError)
+    # Database adapters are here to solve SQL problems in the
+    # most idiomatic way in each database
+    class Base
+      attr_reader :name
+
+      def initialize(name)
+        @name = name
+      end
+
+      # @param [Symbol] interval
+      # @return [Boolean]
+      def allowed_datetime_hierarchy?(interval)
+        datetime_hierarchies.include?(interval.try(:to_sym))
+      end
+
+      protected
+
+      # Allowed datetime hierchies in each adapter
+      # By default (:sqlite) there is none
+      #
+      # @return [Array<Symbol>]
+      def datetime_hierarchies
+        @datetime_hierarchies ||= []
+      end
+    end
+  end
+end

lib/active_reporting/database_adapters/factory.rb

@@ -0,0 +1,27 @@
+# frozen_string_literal: true
+
+module ActiveReporting
+  module DatabaseAdapters
+    class Factory
+      class << self
+        ADAPTERS = {
+          sqlite3: SqliteAdapter,
+          mysql2: MysqlAdapter,
+          postgresql: PostgresqlAdapter,
+          postgis: PostgresqlAdapter
+        }.freeze
+        # @param [Symbol]
+        def for_database(adapter_name)
+          adapter = ADAPTERS[adapter_name]
+
+          return adapter.new(adapter_name) unless adapter.nil?
+
+          raise(
+            DatabaseNotSupported,
+            "Database with this #{adapter_name} is not supported by ActiveReporting"
+          )
+        end
+      end
+    end
+  end
+end

lib/active_reporting/database_adapters/mysql_adapter.rb

@@ -0,0 +1,56 @@
+# frozen_string_literal: true
+
+module ActiveReporting
+  module DatabaseAdapters
+    # Database adapters are here to solve SQL problems in the
+    # most idiomatic way in each database
+    class MysqlAdapter < Base
+      # Generate SQL snippet with DATE_TRUNC
+      # @param [String] interval
+      # @param [String] field
+      # @return [String]
+      def date_trunc(interval, field)
+        clean_sql(
+          <<-SQL
+            DATE_ADD(
+              "#{super_old_base_date}",
+              INTERVAL TIMESTAMPDIFF(
+                #{interval.upcase},
+                "#{super_old_base_date}",
+                #{field}
+              ) #{interval.upcase}
+            )
+          SQL
+        )
+      end
+
+      protected
+
+      # Remove spaces and put all in one line
+      def clean_sql(sql)
+        sql
+          .strip
+          .gsub(/\n+/, ' ')
+          .gsub(/\s+/, ' ')
+          .gsub(/\(\s+\)/, '(')
+          .gsub(/\)\s+\)/, ')')
+      end
+
+      def datetime_hierarchies
+        @datetime_hierarchies ||= %i[
+          year
+          month
+          week
+        ]
+      end
+
+      # Used to generate a diff when implementing
+      # datetime truncation
+      #
+      # @return [String]
+      def super_old_base_date
+        '1900-01-01'
+      end
+    end
+  end
+end

lib/active_reporting/database_adapters/postgresql_adapter.rb

@@ -0,0 +1,38 @@
+# frozen_string_literal: true
+
+module ActiveReporting
+  module DatabaseAdapters
+    class PostgresqlAdapter < Base
+      # Values for the Postgres `date_trunc` method.
+      # See https://www.postgresql.org/docs/10/static/functions-datetime.html#FUNCTIONS-DATETIME-TRUNC
+
+      # Generate SQL snippet with DATE_TRUNC
+      # @param [String] interval
+      # @param [String] field
+      # @return [String]
+      def date_trunc(interval, field)
+        "DATE_TRUNC('#{interval}', #{field})"
+      end
+
+      protected
+
+      def datetime_hierarchies
+        @datetime_hierarchies ||= %i[
+          microseconds
+          milliseconds
+          second
+          minute
+          hour
+          day
+          week
+          month
+          quarter
+          year
+          decade
+          century
+          millennium
+        ]
+      end
+    end
+  end
+end

lib/active_reporting/database_adapters/sqlite_adapter.rb

@@ -0,0 +1,8 @@
+# frozen_string_literal: true
+
+module ActiveReporting
+  module DatabaseAdapters
+    class SqliteAdapter < Base
+    end
+  end
+end

lib/active_reporting/reporting_dimension.rb

@@ -4,11 +4,6 @@
 module ActiveReporting
   class ReportingDimension
     extend Forwardable
-    SUPPORTED_DBS = %w[PostgreSQL PostGIS].freeze
-    # Values for the Postgres `date_trunc` method.
-    # See https://www.postgresql.org/docs/10/static/functions-datetime.html#FUNCTIONS-DATETIME-TRUNC
-    DATETIME_HIERARCHIES = %i[microseconds milliseconds second minute hour day week month quarter year decade
-                              century millennium].freeze
     def_delegators :@dimension, :name, :type, :klass, :association, :model, :hierarchical?, :datetime?
 
     def self.build_from_dimensions(fact_model, dimensions)
@@ -85,7 +80,6 @@ def determine_label(label)
 
     def validate_hierarchical_label(hierarchical_label)
       if datetime?
-        validate_supported_database_for_datetime_hierarchies
         validate_against_datetime_hierarchies(hierarchical_label)
       else
         validate_dimension_is_hierachical(hierarchical_label)
@@ -96,34 +90,35 @@ def validate_hierarchical_label(hierarchical_label)
 
     def validate_dimension_is_hierachical(hierarchical_label)
       return if hierarchical?
-      raise InvalidDimensionLabel, "#{name} must be hierarchical to use label #{hierarchical_label}"
-    end
 
-    def validate_supported_database_for_datetime_hierarchies
-      return if SUPPORTED_DBS.include?(model.connection.adapter_name)
-      raise InvalidDimensionLabel,
-            "Cannot utilize datetime grouping for #{name}; " \
-            "database #{model.connection.adapter_name} is not supported"
+      raise InvalidDimensionLabel, "#{name} must be hierarchical to use label #{hierarchical_label}"
     end
 
     def validate_against_datetime_hierarchies(hierarchical_label)
-      return if DATETIME_HIERARCHIES.include?(hierarchical_label.to_sym)
+      return if Configuration.db_adapter.allowed_datetime_hierarchy?(hierarchical_label)
+
       raise InvalidDimensionLabel, "#{hierarchical_label} is not a valid datetime grouping label in #{name}"
     end
 
     def validate_against_fact_model_properties(hierarchical_label)
       return if dimension_fact_model.hierarchical_levels.include?(hierarchical_label.to_sym)
+
       raise InvalidDimensionLabel, "#{hierarchical_label} is not a hierarchical label in #{name}"
     end
 
     def degenerate_fragment
       return "#{name}_#{@label}" if datetime?
+
       "#{model.quoted_table_name}.#{name}"
     end
 
     def degenerate_select_fragment
-      return "DATE_TRUNC('#{@label}', #{model.quoted_table_name}.#{name}) AS #{name}_#{@label}" if datetime?
-      "#{model.quoted_table_name}.#{name}"
+      return "#{model.quoted_table_name}.#{name}" unless datetime?
+
+      date_trunc = Configuration.db_adapter.date_trunc(
+        @label, "#{model.quoted_table_name}.#{name}"
+      )
+      "#{date_trunc} AS #{name}_#{@label}"
     end
 
     def identifier_fragment