CODEWITHSUNDEEP
ruby
Casey Clayton
Casey Clayton

Reputation: 70

Writing hash information to file and reloading it automatically on program startup?

I wrote a little program that creates a hash called movies. Then I can add, update, delete, and display all current movies in the hash by typing the title.

Instead of having it start a new hash each time and save anything added to a file, and, when updated or deleted, update or delete the key, value pair from the file, I want the program to auto-load the file on startup and create it if it doesn't exist.

I have no idea how to go about doing this.

After reading a lot of the comments I have decided that maybe I should do this with SQL instead, seems like a much better approach!

Upvotes: 0

Views: 130

Answers (2)

vgoff
vgoff

Reputation: 11313

You have the ability to marshal your code in a few ways.

YAML if you would like to use a gem, or JSON. There is also a built in Marshal

RI tells us:

Marshal

(from ruby site) ----------------------------------------------------------------------------- The marshaling library converts collections of Ruby objects into a byte stream, allowing them to be stored outside the currently active script. This data may subsequently be read and the original objects reconstituted.

Marshaled data has major and minor version numbers stored along with the object information. In normal use, marshaling can only load data written with the same major version number and an equal or lower minor version number. If Ruby's ``verbose'' flag is set (normally using -d, -v, -w, or --verbose) the major and minor numbers must match exactly. Marshal versioning is independent of Ruby's version numbers. You can extract the version by reading the first two bytes of marshaled data.

And I will leave it at that for Marshal. But there is a bit more documentation there.

You can also use IO#puts to write to a file, and then modify that file to load later, which I use sometimes for config settings. Why use YAML or another external source, when Ruby is easy enough to have a user modify? You use YAML when it needs to be more generally accessible, as the Tin Man points out.

For example this file is the sample file, but is intended for interactive editing (with constraints, of course) but it is simply valid Ruby. And it gets read by a Ruby program, and is a valid object (in this case a Hash stored in a constant.)

Upvotes: 0

David Grayson
David Grayson

Reputation: 87386

You can't store Ruby objects directly on the disk; you will first need to convert them to some sequence of bytes (i.e. a string). This is called serialization, and there are several different ways to do it and several different formats the data could be in. I think I would recommend JSON, but you might also want to try YAML or Marshal.

Any of those libraries will allow you to convert your hash into a string and allow you to convert that same string back into a hash. Then you can use Ruby's File class to save and load that string from the disk.

This should get you pointed in the right direction. From here you can search for more specific things like "how do I convert a hash to JSON" or "how do I write a string to a file".

Upvotes: 1

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