introduce `conn.data_source_exists?` and `conn.data_sources`.

These new methods are used from the Active Record model layer to
determine which relations are viable to back a model. These new methods
allow us to change `conn.tables` in the future to only return tables and
no views. Same for `conn.table_exists?`.

The goal is to provide the following introspection methods on the
connection:

* `tables`
* `table_exists?`
* `views`
* `view_exists?`
* `data_sources` (views + tables)
* `data_source_exists?` (views + tables)

1 files changed, 14 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 40175c8c8c..285b4065b1 100644
--- a/activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb
+++ b/activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb
@@ -23,6 +23,20 @@ module ActiveRecord
         table_name[0...table_alias_length].tr('.', '_')
       end
 
+      # Returns the relation names useable to back Active Record models.
+      # For most adapters this means all #tables and #views.
+      def data_sources
+        tables | views
+      end
+
+      # Checks to see if the data source +name+ exists on the database.
+      #
+      #   data_source_exists?(:ebooks)
+      #
+      def data_source_exists?(name)
+        data_sources.include?(name.to_s)
+      end
+
       # Returns an array of table names defined in the database.
       def tables(name = nil)
         raise NotImplementedError, "#tables is not implemented"