Abort migration if a given table refer by other tables using foreign key constraints

lib/lhm/migrator.rb

@@ -187,6 +187,11 @@ def validate
         error("could not find origin table #{ @origin.name }")
       end
 
+      unless @origin.satisfies_references_column_requirement?
+        tables = @origin.references.map{|a| "#{a['table_name']}:#{a['constraint_name']}"}.join(', ')
+        error("foreign key constraint fails for tables (#{tables}); before running LHM migration you need to drop this foreign keys;")
+      end
+
       unless @origin.satisfies_id_column_requirement?
         error('origin does not satisfy `id` key requirements')
       end

lib/lhm/table.rb

@@ -5,21 +5,26 @@
 
 module Lhm
   class Table
-    attr_reader :name, :columns, :indices, :pk, :ddl
+    attr_reader :name, :columns, :indices, :pk, :ddl, :references
 
     def initialize(name, pk = 'id', ddl = nil)
       @name = name
       @columns = {}
       @indices = {}
       @pk = pk
       @ddl = ddl
+      @references = []
     end
 
     def satisfies_id_column_requirement?
       !!((id = columns['id']) &&
         id[:type] =~ /(bigint|int)\(\d+\)/)
     end
 
+    def satisfies_references_column_requirement?
+        !references.any?
+    end
+
     def destination_name
       "lhmn_#{ @name }"
     end
@@ -64,6 +69,10 @@ def parse
           extract_indices(read_indices).each do |idx, columns|
             table.indices[idx] = columns
           end
+
+          extract_references(read_references).each do |columns|
+            table.references << columns
+          end
         end
       end
 
@@ -85,6 +94,16 @@ def read_indices
         }
       end
 
+      def read_references
+          @connection.select_all %Q{
+          select constraint_name,table_name, table_schema, column_name
+            from information_schema.key_column_usage
+          where referenced_table_name = '#{ @table_name }'
+            and referenced_table_schema = '#{ @schema_name }'
+          }
+      end
+
+
       def extract_indices(indices)
         indices.
           map do |row|
@@ -111,6 +130,11 @@ def extract_primary_key(schema)
 
         keys.length == 1 ? keys.first : keys
       end
+
+      def extract_references(references)
+        references
+      end
+
     end
   end
 end

spec/fixtures/fk_child_table.ddl

@@ -0,0 +1,6 @@
+CREATE TABLE `fk_child_table` (
+  `id` int(11) NOT NULL AUTO_INCREMENT,
+  `origin_table_id` int(11) NOT NULL,
+  PRIMARY KEY (`id`),
+  CONSTRAINT `fk_origin_table_id` FOREIGN KEY (`origin_table_id`) REFERENCES `origin_example` (`id`)
+) ENGINE=InnoDB DEFAULT CHARSET=utf8

spec/fixtures/origin_example.ddl

@@ -0,0 +1,6 @@
+CREATE TABLE `origin_example` (
+  `id` int(11) NOT NULL AUTO_INCREMENT,
+  `user_id` int(11) NOT NULL,
+  `master_id` int(11) NOT NULL,
+  PRIMARY KEY (`id`)
+) ENGINE=InnoDB DEFAULT CHARSET=utf8

spec/integration/references_spec.rb

@@ -0,0 +1,65 @@
+# Copyright (c) 2011 - 2013, SoundCloud Ltd., Rany Keddo, Tobias Bielohlawek, Tobias
+# Schmidt
+
+require File.expand_path(File.dirname(__FILE__)) + '/integration_helper'
+
+require 'lhm'
+
+describe Lhm do
+  include IntegrationHelper
+
+
+    describe 'the simplest case' do
+      before(:each) do
+        connect_master!
+        Lhm.cleanup(true)
+        %w(fk_child_table origin_example).each do |table|
+          execute "drop table if exists #{table}"
+        end
+        %w(origin_example fk_child_table).each do |table|
+          execute "drop table if exists `fk_child_table`"
+          table_create(table)
+      end
+    end
+
+    after(:each) do
+      Lhm.cleanup(true)
+    end
+
+    it 'should show the foreign key constraints for given table' do
+      actual = table_read(:origin_example).references
+      expected = [{
+        "constraint_name"=> "fk_origin_table_id",
+        "table_name"=> "fk_child_table",
+        "table_schema"=> "lhm",
+        "column_name"=> "origin_table_id"
+        }]
+      actual.must_equal(expected)
+    end
+
+    it 'should raise an exception for foreign key constraint fails for referencing tables' do
+      exception = assert_raises(Exception) {
+        Lhm.change_table(:origin_example) do |t|
+          t.add_column(:new_column, "INT(12) DEFAULT '0'")
+        end
+      }
+      references = table_read(:origin_example).references
+      tables = references.map{|a| "#{a['table_name']}:#{a['constraint_name']}"}.join(', ')
+      message = "foreign key constraint fails for tables (#{tables}); before running LHM migration you need to drop this foreign keys;"
+      assert_equal(message, exception.message )
+    end
+
+    it 'should add a column after droping foreign key constraints' do
+      execute "alter table `fk_child_table` drop foreign key `fk_origin_table_id`"
+      Lhm.change_table(:origin_example) do |t|
+        t.add_column(:new_column, "INT(12) DEFAULT '0'")
+      end
+      connect_master!
+      table_read(:origin_example).columns['new_column'].must_equal({
+        :type => 'int(12)',
+        :is_nullable => 'YES',
+        :column_default => '0',
+      })
+    end
+  end
+end

spec/unit/table_spec.rb

@@ -20,6 +20,11 @@ def set_columns(table, columns)
       table.instance_variable_set('@columns', columns)
     end
 
+    def set_references(table, references)
+      table.instance_variable_set('@references', references)
+    end
+
+
     it 'should be satisfied with a single column primary key called id' do
       @table = Lhm::Table.new('table', 'id')
       set_columns(@table, { 'id' => { :type => 'int(1)' } })
@@ -37,5 +42,18 @@ def set_columns(table, columns)
       set_columns(@table, { 'id' => { :type => 'varchar(255)' } })
       @table.satisfies_id_column_requirement?.must_equal false
     end
+
+    it 'should be satisfied if origin table not refer by any other table using foreign key' do
+      @table = Lhm::Table.new('table')
+      set_references(@table, [])
+      @table.satisfies_references_column_requirement?.must_equal true
+    end
+
+    it 'should NOT be satisfied if origin table refer by any other table using foreign key' do
+      @table = Lhm::Table.new('table', 'id')
+      set_references(@table, [{"CONSTRAINT_NAME"=>"fk_rails_40ebb3948d", "TABLE_NAME"=>"child_table", "TABLE_SCHEMA"=>"schema", "COLUMN_NAME"=>"table_id"}])
+      @table.satisfies_references_column_requirement?.must_equal false
+    end
+
   end
 end