ROR : Important Points to be noted

> Difference between Ruby load and require:

Ruby programs may be broken up into multiple files, and the most natural way to partition a program is to place each nontrivial class or module into a separate file. These separate files can then be reassembled into a single program (and, if well-designed, can be reused by other programs) using require or load. These are global functions defined in Kernel, but are used like language keywords. The same require method is also used for loading files from the standard library.

load and require serve similar purposes, though require is much more commonly used than load. Both functions can load and execute a specified file of Ruby source code. If the file to load is specified with an absolute path, or is relative to ~ (the user’s home directory), then that specific file is loaded. Usually, however, the file is specified as a relative path, and load and require search for it relative to the directories of Ruby’s load path (details on the load path appear below).

Despite these overall similarities, there are important differences between load and require:

• In addition to loading source code, require can also load binary extensions to Ruby. Binary extensions are, of course, implementation-dependent, but in C-based implementations, they typically take the form of shared library files with extensions like .so or .dll.

• load expects a complete filename including an extension. require is usually passed a library name, with no extension, rather than a filename. In that case, it searches for a file that has the library name as its base name and an appropriate source or native library extension. If a directory contains both an .rb source file and a binary extension file, require will load the source file instead of the binary file.

• load can load the same file multiple times. require tries to prevent multiple loads of the same file. (require can be fooled, however, if you use two different, but equivalent, paths to the same library file. In Ruby 1.9, require expands relative paths to absolute paths, which makes it somewhat harder to fool.) require keeps track of the files that have been loaded by appending them to the global array $" (also known as $LOADED_FEATURES). load does not do this.

• load loads the specified file at the current $SAFE level. require loads the specified library with $SAFE set to 0, even if the code that called require has a higher value for that variable.

> To revert migrations to different version:

rake db:migrate version=19

> Task to delete all migration during deployment:

The delete command is just a convenience for executing rm via run. It just attempts to do an rm -f (note the -f! Use with caution!) on the remote server(s), for the named file. To do a recursive delete, pass :recursive => true:

Demonstrating delete [ruby]

delete “#{release_path}/db/migrate“, :recursive => true

Difference between Mocks and Stubs

• Many developers confuse the ideas behind stubbing and mocking. Stubbing simply replaces a real-world implementation with a simpler implementation. A stub can replace full login system with a simple substitute. A stub’s job is to simulate the real world. Mocks are not stubs. A mock object, instead, is like a gauge that measures the way your application uses an interface.
• Stubs provide canned answers to calls made during the test, usually not responding at all to anything outside what’s programmed in for the test. Stubs may also record information about calls, such as an email gateway stub that remembers the messages it ‘sent’, or maybe only how many messages it ‘sent’.
• Mocks are what we are talking about here: objects pre-programmed with expectations which form a specification of the calls they are expected to receive.

Rspec Definitions for Mock and Stubs:Mocks are objects that allow you to set and verify expectations. They are very useful for specifying how the subject of the spec interacts with its collaborators. This approach is widely known as “interaction testing”.Mocks are also very powerful (though less widely understood) as a design tool. As you are driving the implementation of a given class, Mocks provide an amorphous collaborator that can change in behaviour as quickly as you can write an expectation in your spec. These changes are tantamount to designing the interface to a collaborator that often does not yet exist. As the shape of the class being specified becomes more clear, so do the requirements for its collaborators – often leading to the discovery of new types that are needed in your system.
Stubs are objects that allow you to set “stub” responses to messages. Stubs provide canned responses to messages they might receive in a test, while mocks allow you to specify and, subsquently, verify that certain messages should be received during the execution of a test.