1 files changed, 43 insertions, 12 deletions

diff --git a/activerecord/lib/active_record/connection_adapters/schema_cache.rb b/activerecord/lib/active_record/connection_adapters/schema_cache.rb
index dbfe1e4a34..5e30304864 100644
--- a/activerecord/lib/active_record/connection_adapters/schema_cache.rb
+++ b/activerecord/lib/active_record/connection_adapters/schema_cache.rb
@@ -27,7 +27,6 @@ module ActiveRecord
 
       def encode_with(coder)
         coder["columns"]          = @columns
-        coder["columns_hash"]     = @columns_hash
         coder["primary_keys"]     = @primary_keys
         coder["data_sources"]     = @data_sources
         coder["indexes"]          = @indexes
@@ -37,16 +36,21 @@ module ActiveRecord
 
       def init_with(coder)
         @columns          = coder["columns"]
-        @columns_hash     = coder["columns_hash"]
         @primary_keys     = coder["primary_keys"]
         @data_sources     = coder["data_sources"]
         @indexes          = coder["indexes"] || {}
         @version          = coder["version"]
         @database_version = coder["database_version"]
+
+        derive_columns_hash_and_deduplicate_values
       end
 
       def primary_keys(table_name)
-        @primary_keys[table_name] ||= data_source_exists?(table_name) ? connection.primary_key(table_name) : nil
+        @primary_keys.fetch(table_name) do
+          if data_source_exists?(table_name)
+            @primary_keys[deep_deduplicate(table_name)] = deep_deduplicate(connection.primary_key(table_name))
+          end
+        end
       end
 
       # A cached lookup for table existence.
@@ -54,7 +58,7 @@ module ActiveRecord
         prepare_data_sources if @data_sources.empty?
         return @data_sources[name] if @data_sources.key? name
 
-        @data_sources[name] = connection.data_source_exists?(name)
+        @data_sources[deep_deduplicate(name)] = connection.data_source_exists?(name)
       end
 
       # Add internal cache for table with +table_name+.
@@ -73,15 +77,17 @@ module ActiveRecord
 
       # Get the columns for a table
       def columns(table_name)
-        @columns[table_name] ||= connection.columns(table_name)
+        @columns.fetch(table_name) do
+          @columns[deep_deduplicate(table_name)] = deep_deduplicate(connection.columns(table_name))
+        end
       end
 
       # Get the columns for a table as a hash, key is the column name
       # value is the column object.
       def columns_hash(table_name)
-        @columns_hash[table_name] ||= Hash[columns(table_name).map { |col|
-          [col.name, col]
-        }]
+        @columns_hash.fetch(table_name) do
+          @columns_hash[deep_deduplicate(table_name)] = columns(table_name).index_by(&:name)
+        end
       end
 
       # Checks whether the columns hash is already cached for a table.
@@ -90,7 +96,9 @@ module ActiveRecord
       end
 
       def indexes(table_name)
-        @indexes[table_name] ||= connection.indexes(table_name)
+        @indexes.fetch(table_name) do
+          @indexes[deep_deduplicate(table_name)] = deep_deduplicate(connection.indexes(table_name))
+        end
       end
 
       def database_version # :nodoc:
@@ -124,15 +132,38 @@ module ActiveRecord
       def marshal_dump
         # if we get current version during initialization, it happens stack over flow.
         @version = connection.migration_context.current_version
-        [@version, @columns, @columns_hash, @primary_keys, @data_sources, @indexes, database_version]
+        [@version, @columns, {}, @primary_keys, @data_sources, @indexes, database_version]
       end
 
       def marshal_load(array)
-        @version, @columns, @columns_hash, @primary_keys, @data_sources, @indexes, @database_version = array
-        @indexes = @indexes || {}
+        @version, @columns, _columns_hash, @primary_keys, @data_sources, @indexes, @database_version = array
+        @indexes ||= {}
+
+        derive_columns_hash_and_deduplicate_values
       end
 
       private
+        def derive_columns_hash_and_deduplicate_values
+          @columns      = deep_deduplicate(@columns)
+          @columns_hash = @columns.transform_values { |columns| columns.index_by(&:name) }
+          @primary_keys = deep_deduplicate(@primary_keys)
+          @data_sources = deep_deduplicate(@data_sources)
+          @indexes      = deep_deduplicate(@indexes)
+        end
+
+        def deep_deduplicate(value)
+          case value
+          when Hash
+            value.transform_keys { |k| deep_deduplicate(k) }.transform_values { |v| deep_deduplicate(v) }
+          when Array
+            value.map { |i| deep_deduplicate(i) }
+          when String, Deduplicable
+            -value
+          else
+            value
+          end
+        end
+
         def prepare_data_sources
           connection.data_sources.each { |source| @data_sources[source] = true }
         end