First steps towards the join [WIP]

spec/active_record_spec.cr

@@ -48,10 +48,22 @@ module ActiveRecord
     end
   end
 
+  class PostsAuthorIdIs < NullAdapter::Query
+    def call(params, fields)
+      return false unless fields.has_key?("author_id") &&
+                          params.has_key?("1")
+      actual = fields["author_id"].as(Int)
+      expected = params["1"].as(Int32)
+      actual == expected
+    end
+  end
+
   NullAdapter.register_query("(number_of_dependents > :1) AND (number_of_dependents < :2)",
     LessAndMoreDependents.new)
 
   NullAdapter.register_query("number_of_dependents IN (:1, :2)", DependentsIn.new)
+
+  NullAdapter.register_query("posts.author_id = :1", PostsAuthorIdIs.new)
 end
 
 class Example; end
@@ -66,6 +78,8 @@ class Person < ActiveRecord::Model
   field number_of_dependents : Int
   field special_tax_group : Bool
 
+  has_many Post, criteria("posts.author_id") == criteria("people.id")
+
   def get_tax_exemption
     return 0.0 if number_of_dependents < 2
     0.17
@@ -94,6 +108,7 @@ class Post < ActiveRecord::Model
   field title : String
   field content : String
   field created_at : Time
+  field author_id : Int
 
   field_level :protected
 
@@ -378,5 +393,45 @@ module ActiveRecord
         FakeAdapter.instance.table_name.should eq("example_models")
       end
     end
+
+    describe "directive has_many" do
+      it "allows to join people with posts" do
+        # ARRANGE
+        person = new_person.create
+        first_post = Post.create({
+          "title" => "My first post",
+          "content" => "Content",
+          "author_id" => person.id
+        })
+        second_post = Post.create({
+          "title" => "My second post",
+          "content" => "Content",
+          "author_id" => person.id
+        })
+
+        other_person = new_other_person.create
+        other_post = Post.create({
+          "title" => "Other post",
+          "content" => "Content",
+          "author_id" => other_person.id
+        })
+
+        # ACT
+        people_joined_posts = Person.join(Post).all
+        actual = people_joined_posts.first.posts.map &.id
+
+        # ASSERT
+        expected = [first_post, second_post].map &.id
+        actual.should eq(expected)
+      end
+
+      pending "does only one query (an actual join)" do
+
+      end
+
+      pending "also allows to apply where after the join" do
+
+      end
+    end
   end
 end

src/directives/has_many.cr

@@ -0,0 +1,31 @@
+module ActiveRecord::Directives
+  module HasMany
+    macro has_many(foreign_model, query)
+      def self.join(t : {{foreign_model}}.class)
+        HasManyWrapper({{MACRO_CURRENT.last.id}})
+          .new({{foreign_model}}.table_name_value, {{query}})
+      end
+
+      @cached_{{foreign_model.stringify.downcase.id}}s : Array({{foreign_model}})?
+
+      def {{foreign_model.stringify.downcase.id}}s
+        @cached_{{foreign_model.stringify.downcase.id}}s ||=
+          fetch_{{foreign_model.stringify.downcase.id}}s
+      end
+
+      def fetch_{{foreign_model.stringify.downcase.id}}s
+        query = ::Query::Equals[({{query}}).left, id]
+        {{foreign_model}}.where(query)
+      end
+    end
+
+    class HasManyWrapper(T)
+      def initialize(@foreign_table_name : String, @query : ::Query::Query)
+      end
+
+      def all
+        T.all
+      end
+    end
+  end
+end

src/directives/join.cr

@@ -0,0 +1,7 @@
+module ActiveRecord::Directives
+  module Join
+    # macro def join(foreign_model)
+      # {{@type}}::HasMany_{{foreign_model}}
+    # end
+  end
+end

src/model.cr

@@ -1,5 +1,6 @@
 require "./criteria_helper"
 require "./support"
+require "./directives/*"
 
 require "pool/connection"
 
@@ -15,6 +16,9 @@ module ActiveRecord
     include CriteriaHelper
     extend CriteriaHelper
 
+    include Directives::HasMany
+    extend Directives::Join
+
     MACRO_CURRENT = [] of String
 
     DEFAULT_CONNECTION_POOL_CAPACITY =   1
@@ -126,7 +130,7 @@ module ActiveRecord
       @@adapter_name
     end
 
-    private def self.table_name_value
+    def self.table_name_value
       (@@table_name ||= Support.plural(name)).not_nil!
     end