数据类型 
引用
# :string, :text, :integer, :float,:decimal, :datetime, :timestamp, :time, :date,
# :binary, :boolean 

与db有关的rake任务 
 
db:charset 检索当前环境下数据库的字符设置 
db:collation 检索当前环境下数据库的校对 
db:create 用config\database.yml中的定义创建当前 RAILS_ENV 项目环境下的数据库 
db:create:all 用config\database.yml中的定义创建所有数据库 
db:drop 删除当前 droRAILS_ENV项目环境中的数据库 
db:drop:all 删除所有在 config\database.yml中定义的数据库 
db:reset 从db\schema.rb中为当前环境重建数据库（先删后建）. 
db:rollback 回滚(清华出版社一本SQLSERVER书的名词[很奇怪为什么不直接用滚回])数据库到前一个版本. 指定回滚到哪一步要用 STEP=n 参数
db:version 检索当前模式下的版本 

备份数据库
rake db:backup:create 根据database.yml的信息备份数据库
rake db:backup:destroy 默认删除一天前的备份数据
rake db:backup:rebuild 默认恢复最新的备份数据

注意：这里设置的备份目录是db的backup目录，可以修改 

添加索引 
引用

add_index :acls, ["action_id","group_id"],:unique=>true 
add_index :acls, :action_id 

drop all tables 删除全部表
rake db:migrate VERSION=0 

指定恢复/删除：
rake db:migrate:down/up VERSION = version_of_migrati

定义数字精确度 
t.integer :total_price, :precision=>8,:scale=>2,:default=>0


db:create creates the database for the current env
db:create:all creates the databases for all envs
db:drop drops the database for the current env
db:drop:all drops the databases for all envs
db:migrate runs migrations for the current env that have not run yet
db:migrate:up runs one specific migration
db:migrate:down rolls back one specific migration
db:migrate:status shows current migration status
db:rollback rolls back the last migration
db:forward advances the current schema version to the next one
db:seed (only) runs the db/seed.rb file
db:schema:load loads the schema into the current env‘s database
db:schema:dump dumps the current env‘s schema (and seems to create the db as well)
db:setup runs db:schema:load, db:seed
db:reset runs db:drop db:setup
db:migrate:redo runs (db:migrate:down db:migrate:up) or (db:rollback db:migrate) depending on the specified migration
db:migrate:reset runs db:drop db:create db:migrate


rake db:abort_if_pending_migrations                 # Raises an error if there are pending migrations
rake db:charset                                                       # Retrieves the charset for the current environment‘s database
rake db:collation                                                     # Retrieves the collation for the current environment‘s database
rake db:create                                                         # Create the database defined in config/database.yml for the current RAILS_ENV
rake db:create:all                                                   # Create all the local databases defined in config/database.yml
rake db:drop                                                             # Drops the database for the current RAILS_ENV
rake db:drop:all                                                       # Drops all the local databases defined in config/database.yml
rake db:fixtures:identify                                           # Search for a fixture given a LABEL or ID.
rake db:fixtures:load                                             # Load fixtures into the current environment‘s database.
rake db:migrate                                                       # Migrate the database through scripts in db/migrate.
rake db:migrate:down                                          # Runs the "down" for a given migration VERSION.
rake db:migrate:redo                                           # Rollbacks the database one migration and re migrate up.
rake db:migrate:reset                                           # Resets your database using your migrations for the current environment
rake db:migrate:up                                              # Runs the "up" for a given migration VERSION.
rake db:reset                                                       # Drops and recreates the database from db/schema.rb for the current environment.
rake db:rollback                                                   # Rolls the schema back to the previous version.
rake db:schema:dump                                      # Create a db/schema.rb file that can be portably used against any DB supported by AR
rake db:schema:load                                     # Load a schema.rb file into the database
rake db:sessions:clear                                  # Clear the sessions table
rake db:sessions:create                               # Creates a sessions migration for use with CGI::Session::ActiveRecordStore
rake db:structure:dump                              # Dump the database structure to a SQL file
rake db:test:clone                                          # Recreate the test database from the current environment‘s database schema
rake db:test:clone_structure                         # Recreate the test databases from the development structure
rake db:test:load                                             # Recreate the test database from the current schema.rb
rake db:test:prepare                                     # Check for pending migrations and load the test schema
rake db:test:purge                                       # Empty the test database
rake db:version                                 # Retrieves the current schema version number
rake doc:app                        # Build the app HTML Files
rake doc:clobber_app                         # Remove rdoc products
rake doc:clobber_plugins                        # Remove plugin documentation
rake doc:clobber_rails                             # Remove rdoc products
rake doc:guides                                      # Generate Rails guides
rake doc:plugins                                    # Generate documentation for all installed plugins
rake doc:rails                                         # Build the rails HTML Files
rake doc:reapp                                       # Force a rebuild of the RDOC files
rake doc:rerails                                     # Force a rebuild of the RDOC files
rake gems                                               # List the gems that this rails application depends on
rake gems:build                                 # Build any native extensions for unpacked gems
rake gems:install                                         # Installs all required gems for this application.
rake gems:refresh_specs                                 # Regenerate gem specifications in correct format.
rake gems:unpack                                           # Unpacks the specified gem into vendor/gems.
rake gems:unpack:dependencies                                # Unpacks the specified gems and its dependencies into vendor/gems
rake log:clear                                                        # Truncates all *.log files in log/ to zero bytes
rake notes                                   # Enumerate all annotations
rake notes:custom                                     # Enumerate a custom annotation, specify with ANNOTATION=WTFHAX
rake notes:fixme                                       # Enumerate all FIXME annotations
rake notes:optimize                                       # Enumerate all OPTIMIZE annotations
rake notes:todo                                                  # Enumerate all TODO annotations
rake rails:freeze:edge                                         # Lock to latest Edge Rails, for a specific release use RELEASE=1.2.0
rake rails:freeze:gems                                       # Lock this application to the current gems (by unpacking them into vendor/rails)
rake rails:unfreeze                                  # Unlock this application from freeze of gems or edge and return to a fluid use of system gems
rake rails:update                                          # Update both configs, scripts and public/javascripts from Rails
rake rails:update:configs                                    # Update config/boot.rb from your current rails install
rake rails:update:javascripts                                   # Update your javascripts from your current rails install
rake rails:update:scripts                                    # Add new scripts to the application script/ directory
rake routes                                                      # Print out all defined routes in match order, with names.
rake secret                                               # Generate a crytographically secure secret key.
rake stats                                   # Report code statistics (KLOCs, etc) from the application
rake test                                               # Run all unit, functional and integration tests
rake test:benchmark                                # Run tests for benchmarkdb:test:prepare / Benchmark the performance tests
rake test:functionals                                    # Run tests for functionalsdb:test:prepare / Run the functional tests in test/functional
rake test:integration                                    # Run tests for integrationdb:test:prepare / Run the integration tests in test/integration
rake test:plugins                                             # Run tests for pluginsenvironment / Run the plugin tests in vendor/plugins/*/**/test (or specify with PLUGIN=name)
rake test:profile                                              # Run tests for profiledb:test:prepare / Profile the performance tests
rake test:recent                                        # Run tests for recentdb:test:prepare / Test recent changes
rake test:uncommitted                                    # Run tests for uncommitteddb:test:prepare / Test changes since last checkin (only Subversion and Git)
rake test:units                                      # Run tests for unitsdb:test:prepare / Run the unit tests in test/unit
rake time:zones:all                                   # Displays names of all time zones recognized by the Rails TimeZone class, grouped by offset.
rake time:zones:local                                    # Displays names of time zones recognized by the Rails TimeZone class with the same offset as the system local time
rake time:zones:us                                    # Displays names of US time zones recognized by the Rails TimeZone class, grouped by offset.
rake tmp:cache:clear                                  # Clears all files and directories in tmp/cache
rake tmp:clear                                               # Clear session, cache, and socket files from tmp/
rake tmp:create                                               # Creates tmp directories for sessions, cache, and sockets
rake tmp:pids:clear                                                # Clears all files in tmp/pids
rake tmp:sessions:clear                                          # Clears all files in tmp/sessions
rake tmp:sockets:clear                                             # Clears all files in tmp/sockets