set baby steps in the transactions query

app/grids/transactions_query.rb

@@ -0,0 +1,47 @@
+class TransactionsQuery
+  def initialize user
+    @user = user
+    @transactions = Arel::Table.new(:transactions)
+  end
+
+  def arel
+    Arel::SelectManager.new(ActiveRecord::Base)
+      .from(transactions)
+      .project(
+        @transactions[:amount],
+        @transactions[:date],
+        @transactions[:peer_id],
+        @transactions[:issuer_id],
+        @transactions[:message]
+      )
+  end
+
+  def transactions
+    Arel::Nodes::UnionAll.new(outgoing, incoming)
+  end
+
+  def outgoing
+    @transactions
+      .where(@transactions[:debtor_id].eq(@user.id))
+      .project(
+        (@transactions[:amount]*Arel::Nodes::SqlLiteral.new("-1")).as('amount'),
+        @transactions[:creditor_id].as('peer_id'),
+        @transactions[:created_at].as('date'),
+        @transactions[:issuer_id],
+        @transactions[:issuer_type]
+      )
+  end
+
+  def incoming
+    @user.incoming_transactions.arel
+    @transactions
+      .where(@transactions[:debtor_id].eq(@user.id))
+      .project(
+        @transactions[:amount],
+        @transactions[:debtor_id].as('peer_id'),
+        @transactions[:created_at].as('date'),
+        @transactions[:issuer_id],
+        @transactions[:issuer_type]
+      )
+  end
+end