`db:structure:load` and `db:schema:load` no longer purge the database.

Closes #17945

`db:test:prepare` still purges the database to always keep the test
database in a consistent state.

This patch introduces new problems with `db:schema:load`. Prior
to the introduction of foreign-keys, we could run this file against
a non-empty database. Since every `create_table` containted the
`force: true` option, this would recreate tables when loading the schema.

However with foreign-keys in place, `force: true` wont work anymore and
the task will crash.

/cc @schneems

3 files changed, 33 insertions, 2 deletions

diff --git a/activerecord/CHANGELOG.md b/activerecord/CHANGELOG.md
index 72b770e2d5..28441e598e 100644
--- a/activerecord/CHANGELOG.md
+++ b/activerecord/CHANGELOG.md
@@ -1,3 +1,11 @@
+*   `db:schema:load` and `db:structure:load` no longer purge the database
+    before loading the schema. This is left for the user to do.
+    `db:test:prepare` will still purge the database.
+
+    Closes #17945.
+
+    *Yves Senn*
+
 *   Fix undesirable RangeError by Type::Integer. Add Type::UnsignedInteger.
 
     *Ryuta Kamizono*
diff --git a/activerecord/lib/active_record/tasks/database_tasks.rb b/activerecord/lib/active_record/tasks/database_tasks.rb
index 1228de2bfd..6ed610e5f0 100644
--- a/activerecord/lib/active_record/tasks/database_tasks.rb
+++ b/activerecord/lib/active_record/tasks/database_tasks.rb
@@ -214,12 +214,10 @@ module ActiveRecord
         case format
         when :ruby
           check_schema_file(file)
-          purge(configuration)
           ActiveRecord::Base.establish_connection(configuration)
           load(file)
         when :sql
           check_schema_file(file)
-          purge(configuration)
           structure_load(configuration, file)
         else
           raise ArgumentError, "unknown format #{format.inspect}"
diff --git a/railties/test/application/rake/dbs_test.rb b/railties/test/application/rake/dbs_test.rb
index 0a5873bcbf..c414732f92 100644
--- a/railties/test/application/rake/dbs_test.rb
+++ b/railties/test/application/rake/dbs_test.rb
@@ -156,6 +156,31 @@ module ApplicationTests
         end
       end
 
+      test 'db:schema:load and db:structure:load do not purge the existing database' do
+        Dir.chdir(app_path) do
+          `bin/rails runner 'ActiveRecord::Base.connection.create_table(:posts) {|t| t.string :title }'`
+
+          app_file 'db/schema.rb', <<-RUBY
+            ActiveRecord::Schema.define(version: 20140423102712) do
+              create_table(:comments) {}
+            end
+          RUBY
+
+          list_tables = lambda { `bin/rails runner 'p ActiveRecord::Base.connection.tables'`.strip }
+
+          assert_equal '["posts"]', list_tables[]
+          `bin/rake db:schema:load`
+          assert_equal '["posts", "comments", "schema_migrations"]', list_tables[]
+
+          app_file 'db/structure.sql', <<-SQL
+            CREATE TABLE "users" ("id" INTEGER PRIMARY KEY AUTOINCREMENT NOT NULL, "name" varchar(255));
+          SQL
+
+          `bin/rake db:structure:load`
+          assert_equal '["posts", "comments", "schema_migrations", "users"]', list_tables[]
+        end
+      end
+
       def db_test_load_structure
         Dir.chdir(app_path) do
           `rails generate model book title:string;