add Mermaid support

examples/generate.rb

@@ -3,6 +3,7 @@
 
 require "active_record"
 require "rails_erd/diagram/graphviz"
+require "rails_erd/diagram/mermaid"
 require "active_support/dependencies"
 
 output_dir = File.expand_path("output", ".")
@@ -44,9 +45,17 @@
         # Generate ERD.
         outfile = RailsERD::Diagram::Graphviz.new(domain, default_options.merge(specific_options)).create
 
-        puts "   - #{notation} notation saved to #{outfile}"
+        puts "   - Graphviz #{notation} notation saved to #{outfile}"
       end
     end
+
+    filename = File.expand_path("#{output_dir}/#{name}", File.dirname(__FILE__))
+    default_options = { :filetype => "txt", :filename => filename }
+    specific_options = eval((File.read("#{path}/options.rb") rescue "")) || {}
+
+    outfile = RailsERD::Diagram::Mermaid.new(domain, default_options.merge(specific_options)).create
+    puts "   - Mermaid saved to #{outfile}"
+
     puts
   ensure
     # Completely remove all loaded Active Record models.

lib/rails_erd.rb

@@ -36,6 +36,7 @@ class << self
 
     def default_options
       ActiveSupport::OrderedOptions[
+        :generator, :graphviz,
         :attributes, :content,
         :disconnected, true,
         :filename, "erd",

lib/rails_erd/cli.rb

@@ -5,14 +5,19 @@
   separator ""
   separator "Diagram options:"
 
+  option :generator do
+    long "--generator=Generator"
+    desc "Generator to use (graphviz or mermaid). Defaults to graphviz."
+  end
+
   option :title do
     long "--title=TITLE"
     desc "Replace default diagram title with a custom one."
   end
 
   option :notation do
     long "--notation=STYLE"
-    desc "Diagram notation style, one of simple, bachman, uml or crowsfoot."
+    desc "Diagram notation style, one of simple, bachman, uml or crowsfoot (avaiable only with Graphviz engine)."
   end
 
   option :attributes do
@@ -159,7 +164,7 @@ def start
 
     def initialize(path, options)
       @path, @options = path, options
-      require "rails_erd/diagram/graphviz"
+      require "rails_erd/diagram/graphviz" if options.generator == :graphviz
     end
 
     def start
@@ -196,9 +201,17 @@ def load_application
     rescue TypeError
     end
 
+    def generator
+      if options.generator == :mermaid
+        RailsERD::Diagram::Mermaid
+      else
+        RailsERD::Diagram::Graphviz
+      end
+    end
+
     def create_diagram
       $stderr.puts "Generating entity-relationship diagram for #{ActiveRecord::Base.descendants.length} models..."
-      file = RailsERD::Diagram::Graphviz.create(options)
+      file = generator.create(options)
       $stderr.puts "Diagram saved to '#{file}'."
       `open #{file}` if options[:open]
     end

lib/rails_erd/config.rb

@@ -61,7 +61,7 @@ def normalize_value(key, value)
         end
 
       # <symbol>
-      when :filetype, :notation
+      when :filetype, :notation, :generator
         value.to_sym
 
       # [<string>]

lib/rails_erd/diagram/mermaid.rb

@@ -0,0 +1,78 @@
+# encoding: utf-8
+require "rails_erd/diagram"
+require "erb"
+
+module RailsERD
+  class Diagram
+    class Mermaid < Diagram
+
+      attr_accessor :graph
+
+      setup do
+        self.graph = ["classDiagram"]
+
+        # hard code to RL to make it easier to view diagrams from GitHub
+        self.graph << "\tdirection RL"
+      end
+
+      each_entity do |entity, attributes|
+        graph << "\tclass `#{entity}`"
+
+        attributes.each do | attr|
+          graph << "\t`#{entity}` : +#{attr.type} #{attr.name}"
+        end
+      end
+
+      each_specialization do |specialization|
+        from, to = specialization.generalized, specialization.specialized
+        graph << "\t<<polymorphic>> `#{specialization.generalized}`"
+        graph << "\t #{from.name} <|-- #{to.name}"
+      end
+
+      each_relationship do |relationship|
+        from, to = relationship.source, relationship.destination
+        graph << "\t`#{from.name}` #{relation_arrow(relationship)} `#{to.name}`"
+
+        from.children.each do |child|
+          graph << "\t`#{child.name}` #{relation_arrow(relationship)} `#{to.name}`"
+        end
+
+        to.children.each do |child|
+          graph << "\t`#{from.name}` #{relation_arrow(relationship)} `#{child.name}`"
+        end
+      end
+
+      save do
+        raise "Saving diagram failed!\nOutput directory '#{File.dirname(filename)}' does not exist." unless File.directory?(File.dirname(filename))
+
+        File.write(filename.gsub(/\s/,"_"), graph.uniq.join("\n"))
+        filename
+      end
+
+      def filename
+        "#{options.filename}.mmd"
+      end
+
+      def relation_arrow(relationship)
+        arrow_body = arrow_body relationship
+        arrow_head = arrow_head relationship
+        arrow_tail = arrow_tail relationship
+
+        "#{arrow_tail}#{arrow_body}#{arrow_head}"
+      end
+
+      def arrow_body(relationship)
+        relationship.indirect? ? ".." : "--"
+      end
+
+      def arrow_head(relationship)
+        relationship.to_many? ?  ">" : ""
+      end
+
+      def arrow_tail(relationship)
+        relationship.many_to? ? "<" : ""
+      end
+
+    end
+  end
+end

lib/rails_erd/tasks.rake

@@ -8,10 +8,12 @@ end
 
 namespace :erd do
   task :check_dependencies do
-    include GraphViz::Utils
-    unless find_executable("dot", nil)
-      raise "Unable to find GraphViz's \"dot\" executable. Please " \
-            "visit https://voormedia.github.io/rails-erd/install.html for installation instructions."
+    if RailsERD.options.generator == :graphviz
+      include GraphViz::Utils
+      unless find_executable("dot", nil)
+        raise "#{RailsERD.options.generator} Unable to find GraphViz's \"dot\" executable. Please " \
+              "visit https://voormedia.github.io/rails-erd/install.html for installation instructions."
+      end
     end
   end
 
@@ -58,13 +60,22 @@ namespace :erd do
     raise "Active Record was not loaded." unless defined? ActiveRecord
   end
 
-  task :generate => [:check_dependencies, :options, :load_models] do
+  task :generate => [:options, :check_dependencies, :load_models] do
     include ErdRakeHelper
 
     say "Generating Entity-Relationship Diagram for #{ActiveRecord::Base.descendants.length} models..."
 
-    require "rails_erd/diagram/graphviz"
-    file = RailsERD::Diagram::Graphviz.create
+    file = case RailsERD.options.generator
+    when :mermaid
+      require "rails_erd/diagram/mermaid"
+      RailsERD::Diagram::Mermaid.create
+    when :graphviz
+      require "rails_erd/diagram/graphviz"
+      RailsERD::Diagram::Graphviz.create
+    else
+      raise "Unknown generator: #{RailsERD.options.generator}"
+    end
+
 
     say "Done! Saved diagram to ./#{file}"
   end