Supporting multiple connections.

This is the first I've gotten this to work. Some refactoring needs to be
done as well as specs.

src/clear/model/model.cr

@@ -14,6 +14,7 @@ module Clear::Model
   include Clear::Model::HasValidation
   include Clear::Model::HasRelations
   include Clear::Model::HasScope
+  include Clear::Model::Connection
   include Clear::Model::ClassMethods
   include Clear::Model::IsPolymorphic
 

src/clear/model/modules/class_methods.cr

@@ -20,7 +20,7 @@ module Clear::Model::ClassMethods
       class Collection < Clear::Model::CollectionBase(\{{@type}}); end
 
       def self.query
-        Collection.new.from(table)
+        Collection.new.use_connection(connection).from(table)
       end
 
       def self.find(x)

src/clear/model/modules/connection.cr

@@ -0,0 +1,7 @@
+module Clear::Model::Connection
+  macro included # When included into Model
+    macro included # When included into final Model
+      class_property connection : Clear::SQL::Symbolic = "default"
+    end
+  end
+end

src/clear/sql/insert_query.cr

@@ -18,6 +18,7 @@ require "./query/*"
 #
 class Clear::SQL::InsertQuery
   include Query::Change
+  include Query::Connection
 
   alias Inserable = ::Clear::SQL::Any | BigInt | BigFloat | Time
   getter keys : Array(Symbolic) = [] of Symbolic
@@ -32,7 +33,7 @@ class Clear::SQL::InsertQuery
     Clear::SQL.log_query to_sql do
       h = {} of String => ::Clear::SQL::Any
 
-      Clear::SQL.connection.query(to_sql) do |rs|
+      Clear::SQL.connection(self.connection_name).query(to_sql) do |rs|
         fetch_result_set(h, rs) { |x| yield(x) }
       end
     end

src/clear/sql/query/connection.cr

@@ -0,0 +1,9 @@
+module Clear::SQL
+  module Query::Connection
+    getter connection_name : Symbolic = "default"
+
+    def use_connection(@connection_name : Symbolic)
+      self
+    end
+  end
+end

src/clear/sql/query/fetch.cr

@@ -23,7 +23,7 @@ module Clear::SQL::Query::Fetch
     trigger_before_query
 
     Clear::SQL.transaction do
-      cnx = Clear::SQL.connection
+      cnx = Clear::SQL.connection(self.connection_name)
       cursor_name = "__cursor_#{Time.now.epoch ^ (rand * 0xfffffff).to_i}__"
 
       cursor_declaration = "DECLARE #{cursor_name} CURSOR FOR #{to_sql}"
@@ -55,7 +55,7 @@ module Clear::SQL::Query::Fetch
     trigger_before_query
 
     Clear::SQL.log_query to_sql do
-      Clear::SQL.connection.scalar(to_sql).as(T)
+      Clear::SQL.connection(self.connection_name).scalar(to_sql).as(T)
     end
   end
 
@@ -71,7 +71,7 @@ module Clear::SQL::Query::Fetch
     to_sql = self.to_sql
 
     rs = uninitialized PG::ResultSet
-    Clear::SQL.log_query(to_sql) { rs = Clear::SQL.connection.query(to_sql) }
+    Clear::SQL.log_query(to_sql) { rs = Clear::SQL.connection(self.connection_name).query(to_sql) }
 
     o = [] of Hash(String, ::Clear::SQL::Any)
     fetch_result_set(h, rs) { |x| o << x.dup }
@@ -92,7 +92,8 @@ module Clear::SQL::Query::Fetch
     to_sql = self.to_sql
 
     rs = uninitialized PG::ResultSet
-    Clear::SQL.log_query(to_sql) { rs = Clear::SQL.connection.query(to_sql) }
+
+    Clear::SQL.log_query(to_sql) { rs = Clear::SQL.connection(connection_name).query(to_sql) }
 
     if fetch_all
       o = [] of Hash(String, ::Clear::SQL::Any)

src/clear/sql/select_builder.cr

@@ -17,6 +17,7 @@ module Clear::SQL::SelectBuilder
   end
 
   include Query::Change
+  include Query::Connection
   include Query::Select
   include Query::From
   include Query::Join

src/clear/sql/sql.cr

@@ -49,13 +49,17 @@ module Clear
     include Clear::SQL::Logger
     extend self
 
-    @@connection : DB::Database?
+    @@connections : Hash(Symbolic, DB::Database?)?
 
-    def self.connection : DB::Database
-      if @@connection
-        @@connection.not_nil!
+    def self.connection(connection) : DB::Database
+      if @@connections.nil?
+        raise "No database connections have been defined"
       else
-        raise "The database connection is not initialized"
+        if connection = @@connections.not_nil![connection]
+          connection.not_nil!
+        else
+          raise "The database connection is not initialized"
+        end
       end
     end
 
@@ -68,7 +72,15 @@ module Clear
     end
 
     def init(url : String)
-      @@connection = DB.open(url)
+      @@connections ||= {} of Symbolic => DB::Database?
+      @@connections.not_nil!["default"] = DB.open(url)
+    end
+
+    def init(connections : Hash(Symbolic, String))
+      @@connections ||= {} of Symbolic => DB::Database?
+      connections.each do |key, connection_string|
+        @@connections.not_nil![key] = DB.open(connection_string)
+      end
     end
 
     @@in_transaction : Bool = false
@@ -146,7 +158,7 @@ module Clear
     # Clear::SQL.execute("SELECT 1 FROM users")
     #
     def execute(sql)
-      log_query(sql) { Clear::SQL.connection.exec(sql) }
+      log_query(sql) { Clear::SQL.connection("default").exec(sql) }
     end
 
     # :nodoc: