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)

5 files changed, 58 insertions, 22 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"
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 feb41e96f0..79a24d1996 100644
--- a/activerecord/lib/active_record/connection_adapters/abstract_mysql_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/abstract_mysql_adapter.rb
@@ -628,6 +628,7 @@ module ActiveRecord
       def tables(name = nil) # :nodoc:
         select_values("SHOW FULL TABLES", 'SCHEMA')
       end
+      alias data_sources tables
 
       def truncate(table_name, name = nil)
         execute "TRUNCATE TABLE #{quote_table_name(table_name)}", name
@@ -644,6 +645,7 @@ module ActiveRecord
 
         select_values(sql, 'SCHEMA').any?
       end
+      alias data_source_exists? table_exists?
 
       def views # :nodoc:
         select_values("SHOW FULL TABLES WHERE table_type = 'VIEW'", 'SCHEMA')
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 66d311dd48..aaf5b2898b 100644
--- a/activerecord/lib/active_record/connection_adapters/postgresql/schema_statements.rb
+++ b/activerecord/lib/active_record/connection_adapters/postgresql/schema_statements.rb
@@ -73,6 +73,16 @@ module ActiveRecord
           select_values("SELECT tablename FROM pg_tables WHERE schemaname = ANY(current_schemas(false))", 'SCHEMA')
         end
 
+        def data_sources # :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 ('r', 'v','m') -- (r)elation/table, (v)iew, (m)aterialized view
+            AND n.nspname = ANY (current_schemas(false))
+          SQL
+        end
+
         # Returns true if table exists.
         # If the schema is not specified as part of +name+ then it will only find tables within
         # the current schema search path (regardless of permissions to access tables in other schemas)
@@ -89,6 +99,7 @@ module ActiveRecord
               AND n.nspname = #{name.schema ? "'#{name.schema}'" : 'ANY (current_schemas(false))'}
           SQL
         end
+        alias data_source_exists? table_exists?
 
         def views # :nodoc:
           select_values(<<-SQL, 'SCHEMA')
diff --git a/activerecord/lib/active_record/connection_adapters/schema_cache.rb b/activerecord/lib/active_record/connection_adapters/schema_cache.rb
index 981d5d7a3c..eee142378c 100644
--- a/activerecord/lib/active_record/connection_adapters/schema_cache.rb
+++ b/activerecord/lib/active_record/connection_adapters/schema_cache.rb
@@ -10,7 +10,7 @@ module ActiveRecord
         @columns      = {}
         @columns_hash = {}
         @primary_keys = {}
-        @tables       = {}
+        @data_sources = {}
       end
 
       def initialize_dup(other)
@@ -18,33 +18,38 @@ module ActiveRecord
         @columns      = @columns.dup
         @columns_hash = @columns_hash.dup
         @primary_keys = @primary_keys.dup
-        @tables       = @tables.dup
+        @data_sources = @data_sources.dup
       end
 
       def primary_keys(table_name)
-        @primary_keys[table_name] ||= table_exists?(table_name) ? connection.primary_key(table_name) : nil
+        @primary_keys[table_name] ||= data_source_exists?(table_name) ? connection.primary_key(table_name) : nil
       end
 
       # A cached lookup for table existence.
-      def table_exists?(name)
-        prepare_tables if @tables.empty?
-        return @tables[name] if @tables.key? name
+      def data_source_exists?(name)
+        prepare_data_sources if @data_sources.empty?
+        return @data_sources[name] if @data_sources.key? name
 
-        @tables[name] = connection.table_exists?(name)
+        @data_sources[name] = connection.data_source_exists?(name)
       end
+      alias table_exists? data_source_exists?
+      deprecate :table_exists? => "use #data_source_exists? instead"
+
 
       # Add internal cache for table with +table_name+.
       def add(table_name)
-        if table_exists?(table_name)
+        if data_source_exists?(table_name)
           primary_keys(table_name)
           columns(table_name)
           columns_hash(table_name)
         end
       end
 
-      def tables(name)
-        @tables[name]
+      def data_sources(name)
+        @data_sources[name]
       end
+      alias tables data_sources
+      deprecate :tables => "use #data_sources instead"
 
       # Get the columns for a table
       def columns(table_name)
@@ -64,36 +69,38 @@ module ActiveRecord
         @columns.clear
         @columns_hash.clear
         @primary_keys.clear
-        @tables.clear
+        @data_sources.clear
         @version = nil
       end
 
       def size
-        [@columns, @columns_hash, @primary_keys, @tables].map(&:size).inject :+
+        [@columns, @columns_hash, @primary_keys, @data_sources].map(&:size).inject :+
       end
 
-      # Clear out internal caches for table with +table_name+.
-      def clear_table_cache!(table_name)
-        @columns.delete table_name
-        @columns_hash.delete table_name
-        @primary_keys.delete table_name
-        @tables.delete table_name
+      # Clear out internal caches for the data source +name+.
+      def clear_data_source_cache!(name)
+        @columns.delete name
+        @columns_hash.delete name
+        @primary_keys.delete name
+        @data_sources.delete name
       end
+      alias clear_table_cache! clear_data_source_cache!
+      deprecate :clear_table_cache! => "use #clear_data_source_cache! instead"
 
       def marshal_dump
         # if we get current version during initialization, it happens stack over flow.
         @version = ActiveRecord::Migrator.current_version
-        [@version, @columns, @columns_hash, @primary_keys, @tables]
+        [@version, @columns, @columns_hash, @primary_keys, @data_sources]
       end
 
       def marshal_load(array)
-        @version, @columns, @columns_hash, @primary_keys, @tables = array
+        @version, @columns, @columns_hash, @primary_keys, @data_sources = array
       end
 
       private
 
-        def prepare_tables
-          connection.tables.each { |table| @tables[table] = true }
+        def prepare_data_sources
+          connection.data_sources.each { |source| @data_sources[source] = true }
         end
     end
   end
diff --git a/activerecord/lib/active_record/connection_adapters/sqlite3_adapter.rb b/activerecord/lib/active_record/connection_adapters/sqlite3_adapter.rb
index e2f52707e8..f6a6e3eb4d 100644
--- a/activerecord/lib/active_record/connection_adapters/sqlite3_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/sqlite3_adapter.rb
@@ -319,10 +319,12 @@ module ActiveRecord
           row['name']
         end
       end
+      alias data_sources tables
 
       def table_exists?(table_name)
         table_name && tables(nil, table_name).any?
       end
+      alias data_source_exists? table_exists?
 
       def views # :nodoc:
         select_values("SELECT name FROM sqlite_master WHERE type = 'view' AND name <> 'sqlite_sequence'", 'SCHEMA')