Add `#views` and `#view_exists?` methods on connection adapters

4 files changed, 66 insertions, 0 deletions

diff --git a/activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb b/activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb
index 08803303cf..43512c6bcc 100644
--- a/activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb
+++ b/activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb
@@ -36,6 +36,19 @@ module ActiveRecord
         tables.include?(table_name.to_s)
       end
 
+      # Returns an array of view names defined in the database.
+      def views
+        raise NotImplementedError, "#views is not implemented"
+      end
+
+      # Checks to see if the view +view_name+ exists on the database.
+      #
+      #   view_exists?(:ebooks)
+      #
+      def view_exists?(view_name)
+        views.include?(view_name.to_s)
+      end
+
       # Returns an array of indexes for the given table.
       # def indexes(table_name, name = nil) end
 
diff --git a/activerecord/lib/active_record/connection_adapters/abstract_mysql_adapter.rb b/activerecord/lib/active_record/connection_adapters/abstract_mysql_adapter.rb
index 597f0d0597..9bb1b0c124 100644
--- a/activerecord/lib/active_record/connection_adapters/abstract_mysql_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/abstract_mysql_adapter.rb
@@ -549,6 +549,22 @@ module ActiveRecord
         tables(nil, schema, table).any?
       end
 
+      def views # :nodoc:
+        select_values("SHOW FULL TABLES WHERE table_type = 'VIEW'", 'SCHEMA')
+      end
+
+      def view_exists?(view_name) # :nodoc:
+        return false unless view_name.present?
+
+        schema, name = view_name.to_s.split('.', 2)
+        schema, name = @config[:database], schema unless name # A view was provided without a schema
+
+        sql = "SELECT table_name FROM information_schema.tables WHERE table_type = 'VIEW'"
+        sql << " AND table_schema = #{quote(schema)} AND table_name = #{quote(name)}"
+
+        select_values(sql, 'SCHEMA').any?
+      end
+
       # Returns an array of indexes for the given table.
       def indexes(table_name, name = nil) #:nodoc:
         indexes = []
diff --git a/activerecord/lib/active_record/connection_adapters/postgresql/schema_statements.rb b/activerecord/lib/active_record/connection_adapters/postgresql/schema_statements.rb
index 69aa02ccf4..777b5ca95f 100644
--- a/activerecord/lib/active_record/connection_adapters/postgresql/schema_statements.rb
+++ b/activerecord/lib/active_record/connection_adapters/postgresql/schema_statements.rb
@@ -90,6 +90,30 @@ module ActiveRecord
           SQL
         end
 
+        def views # :nodoc:
+          select_values(<<-SQL, 'SCHEMA')
+            SELECT c.relname
+            FROM pg_class c
+            LEFT JOIN pg_namespace n ON n.oid = c.relnamespace
+            WHERE c.relkind IN ('v','m') -- (v)iew, (m)aterialized view
+            AND n.nspname = ANY (current_schemas(false))
+          SQL
+        end
+
+        def view_exists?(view_name) # :nodoc:
+          name = Utils.extract_schema_qualified_name(view_name.to_s)
+          return false unless name.identifier
+
+          select_values(<<-SQL, 'SCHEMA').any?
+            SELECT c.relname
+            FROM pg_class c
+            LEFT JOIN pg_namespace n ON n.oid = c.relnamespace
+            WHERE c.relkind IN ('v','m') -- (v)iew, (m)aterialized view
+            AND c.relname = '#{name.identifier}'
+            AND n.nspname = #{name.schema ? "'#{name.schema}'" : 'ANY (current_schemas(false))'}
+          SQL
+        end
+
         def drop_table(table_name, options = {}) # :nodoc:
           execute "DROP TABLE#{' IF EXISTS' if options[:if_exists]} #{quote_table_name(table_name)}#{' CASCADE' if options[:force] == :cascade}"
         end
diff --git a/activerecord/lib/active_record/connection_adapters/sqlite3_adapter.rb b/activerecord/lib/active_record/connection_adapters/sqlite3_adapter.rb
index 24fc67938d..fa7285dca4 100644
--- a/activerecord/lib/active_record/connection_adapters/sqlite3_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/sqlite3_adapter.rb
@@ -325,6 +325,19 @@ module ActiveRecord
         table_name && tables(nil, table_name).any?
       end
 
+      def views # :nodoc:
+        select_values("SELECT name FROM sqlite_master WHERE type = 'view' AND name <> 'sqlite_sequence'", 'SCHEMA')
+      end
+
+      def view_exists?(view_name) # :nodoc:
+        return false unless view_name.present?
+
+        sql = "SELECT name FROM sqlite_master WHERE type = 'view' AND name <> 'sqlite_sequence'"
+        sql << " AND name = #{quote(view_name)}"
+
+        select_values(sql, 'SCHEMA').any?
+      end
+
       # Returns an array of +Column+ objects for the table specified by +table_name+.
       def columns(table_name) #:nodoc:
         table_structure(table_name).map do |field|