Add an :if_not_exists option to create_table

[fatkodima & Stefan Kanev]

activerecord/CHANGELOG.md

@@ -1,3 +1,22 @@
+*   Add an `:if_not_exists` option to `create_table`.
+
+    Example:
+
+        create_table :posts, if_not_exists: true do |t|
+          t.string :title
+        end
+
+    That would execute:
+
+        CREATE TABLE IF NOT EXISTS posts (
+          ...
+        )
+
+    If the table already exists, `if_not_exists: false` (the default) raises an
+    exception whereas `if_not_exists: true` does nothing.
+
+    *fatkodima*, *Stefan Kanev*
+
 *   Defining an Enum as a Hash with blank key, or as an Array with a blank value, now raises an `ArgumentError`.
 
     *Christophe Maximin*

activerecord/lib/active_record/connection_adapters/abstract/schema_creation.rb

@@ -39,7 +39,9 @@ module ActiveRecord
           end
 
           def visit_TableDefinition(o)
-            create_sql = +"CREATE#{' TEMPORARY' if o.temporary} TABLE #{quote_table_name(o.name)} "
+            create_sql = +"CREATE#{' TEMPORARY' if o.temporary} TABLE "
+            create_sql << "IF NOT EXISTS " if o.if_not_exists
+            create_sql << "#{quote_table_name(o.name)} "
 
             statements = o.columns.map { |c| accept c }
             statements << accept(o.primary_keys) if o.primary_keys

activerecord/lib/active_record/connection_adapters/abstract/schema_definitions.rb

@@ -257,14 +257,15 @@ module ActiveRecord
       include ColumnMethods
 
       attr_accessor :indexes
-      attr_reader :name, :temporary, :options, :as, :foreign_keys, :comment
+      attr_reader :name, :temporary, :if_not_exists, :options, :as, :foreign_keys, :comment
 
-      def initialize(name, temporary = false, options = nil, as = nil, comment: nil)
+      def initialize(name, temporary = false, if_not_exists = false, options = nil, as = nil, comment: nil)
         @columns_hash = {}
         @indexes = []
         @foreign_keys = []
         @primary_keys = nil
         @temporary = temporary
+        @if_not_exists = if_not_exists
         @options = options
         @as = as
         @name = name

activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb

@@ -205,6 +205,9 @@ module ActiveRecord
       #   Set to true to drop the table before creating it.
       #   Set to +:cascade+ to drop dependent objects as well.
       #   Defaults to false.
+      # [<tt>:if_not_exists</tt>]
+      #   Set to true to avoid raising an error when the table already exists.
+      #   Defaults to false.
       # [<tt>:as</tt>]
       #   SQL to use to generate the table. When this option is used, the block is
       #   ignored, as are the <tt>:id</tt> and <tt>:primary_key</tt> options.
@@ -288,7 +291,7 @@ module ActiveRecord
       #
       # See also TableDefinition#column for details on how to create columns.
       def create_table(table_name, comment: nil, **options)
-        td = create_table_definition table_name, options[:temporary], options[:options], options[:as], comment: comment
+        td = create_table_definition table_name, options[:temporary], options[:if_not_exists], options[:options], options[:as], comment: comment
 
         if options[:id] != false && !options[:as]
           pk = options.fetch(:primary_key) do

activerecord/test/cases/migration_test.rb

@@ -127,6 +127,36 @@ class MigrationTest < ActiveRecord::TestCase
     assert_equal 20131219224947, migrator.current_version
   end
 
+  def test_create_table_raises_if_already_exists
+    connection = Person.connection
+    connection.create_table :testings, force: true do |t|
+      t.string :foo
+    end
+
+    assert_raise(ActiveRecord::StatementInvalid) do
+      connection.create_table :testings do |t|
+        t.string :foo
+      end
+    end
+  ensure
+    connection.drop_table :testings, if_exists: true
+  end
+
+  def test_create_table_with_if_not_exists_true
+    connection = Person.connection
+    connection.create_table :testings, force: true do |t|
+      t.string :foo
+    end
+
+    assert_nothing_raised do
+      connection.create_table :testings, if_not_exists: true do |t|
+        t.string :foo
+      end
+    end
+  ensure
+    connection.drop_table :testings, if_exists: true
+  end
+
   def test_create_table_with_force_true_does_not_drop_nonexisting_table
     # using a copy as we need the drop_table method to
     # continue to work for the ensure block of the test