Ruby syntax in ActiveRecord-CodePudding

I am currently doing the ruby on rails beginner tutorials and I do not understand the specific syntax of migrations.

class CreateArticles < ActiveRecord::Migration[7.0]
  def change
    create_table :articles do |t|
      t.string :title
      t.text :body

      t.timestamps
    end
  end
end

Specifically, I do not understand the syntax within the method change on line 3.

What does create_table refers to?

What does :articles means? Is it a symbol?

What is the |t| in this case referring to. To a new table?

Any context and deeper explanations of this code would be appreciated.

CodePudding user response：

Ruby libraries often use "DSLs" (domain specific languages). This is an example of one, however once you understand Ruby syntax you can see that it is , in fact, just regular Ruby.

You are right that create_table is a method call, and :articles is a symbol.

Also remember that functions in ruby can take block arguments, which have two possible syntaxes:

[1,2,3].each { |num| <block content> }

# or ..
[1,2,3].each do |num|
  <block content>
end

In here |num| is a block argument. Under the hood, each will take the input and pass each element one-by-one to the block. We refer to the current element by this block argument.

So, taking all this into consideration, we can rewrite this function call like so:

create_table(:articles) do |table|
  <do stuff with table>
end

Remember that the parenthesis are usually optional in Ruby, which is why it can be written as create_table :articles

In more plain language, what this is saying is "create a table with the name articles, and then customize that table with the block". It's inside the block that individual columns are added to the table.

I would recommnend reading up more on Ruby blocks since it's a very valuable and important concept.

If you want to write a method that takes a regular argument and a block, it might look like so:

def my_function(symbol)
  yield(symbol)
end

And then calling it:

my_function :some_symbol do |symbol|
  puts "the value is #{symbol}"
end