fk: add `foreign_keys` for PostgreSQL adapter.

2 files changed, 38 insertions, 0 deletions

diff --git a/activerecord/lib/active_record/connection_adapters/postgresql/schema_definitions.rb b/activerecord/lib/active_record/connection_adapters/postgresql/schema_definitions.rb
index 0867e5ef54..724e3fa1ee 100644
--- a/activerecord/lib/active_record/connection_adapters/postgresql/schema_definitions.rb
+++ b/activerecord/lib/active_record/connection_adapters/postgresql/schema_definitions.rb
@@ -89,6 +89,20 @@ module ActiveRecord
         attr_accessor :array
       end
 
+      class ForeignKeyDefinition < Struct.new(:from_table, :to_table, :options)
+        def name
+          options[:name]
+        end
+
+        def column
+          options[:column]
+        end
+
+        def primary_key
+          options[:primary_key]
+        end
+      end
+
       class TableDefinition < ActiveRecord::ConnectionAdapters::TableDefinition
         include ColumnMethods
 
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 f09ce113d6..b87fb85ae2 100644
--- a/activerecord/lib/active_record/connection_adapters/postgresql/schema_statements.rb
+++ b/activerecord/lib/active_record/connection_adapters/postgresql/schema_statements.rb
@@ -448,6 +448,30 @@ module ActiveRecord
           execute "ALTER INDEX #{quote_column_name(old_name)} RENAME TO #{quote_table_name(new_name)}"
         end
 
+        def foreign_keys(table_name)
+          fk_info = select_all <<-SQL
+SELECT t2.relname AS to_table, a1.attname AS column, a2.attname AS primary_key, c.conname AS name, c.confdeltype AS dependency
+FROM pg_constraint c
+JOIN pg_class t1 ON c.conrelid = t1.oid
+JOIN pg_class t2 ON c.confrelid = t2.oid
+JOIN pg_attribute a1 ON a1.attnum = c.conkey[1] AND a1.attrelid = t1.oid
+JOIN pg_attribute a2 ON a2.attnum = c.confkey[1] AND a2.attrelid = t2.oid
+JOIN pg_namespace t3 ON c.connamespace = t3.oid
+WHERE c.contype = 'f'
+  AND t1.relname = #{quote(table_name)}
+  AND t3.nspname = ANY (current_schemas(false))
+ORDER BY c.conname
+          SQL
+
+          fk_info.map do |row|
+            options = {
+              column: row['column'],
+              name: row['name'],
+              primary_key: row['primary_key'] }
+            ForeignKeyDefinition.new(table_name, row["to_table"], options)
+          end
+        end
+
         def add_foreign_key(from_table, to_table, options = {})
           foreign_key_column = options.fetch(:column)
           referenced_column = "id"