Rails and Ajax

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Rails and Ajax
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HTML Forms

• The ltform argumentsgt ... lt/formgt tag encloses
  form elements (and usually includes other HTML as
  well)
• The arguments to form tell what to do with the
  user input
• actionURL" (required)
• Specifies where to send the data when the Submit
  button is clicked
• method"get" (default)
• Form data is sent as a URL with ?form_data info
  appended to the end
• Can be used only if data is all ASCII and not
  more than 100 characters
• method"post"
• Form data is sent in the body of the URL request
• Cannot be bookmarked by most browsers
• target"target"
• Tells where to open the page sent as a result of
  the request
• target _blank means open in a new window
• target _top means use the same window

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Ruby forms

• In a template, you should use form_tag() instead
  of ltformgt
• The first argument is a hash that tells which
  action to invoke
• This takes the same options as url_for() see
  next slide
• The optional second argument is another hash for
  setting HTML form attributes
• Example lt form_tag actiongtsave ,
  classgt"compact" gt lt end_form_tag gt

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url_for()

• The purpose of url_for is to avoid the need to
  write hardcoded URLs
• url_for takes a hash of options as its parameter
• Options include controller, action, and
  possibly id
• Reasonable defaults are used
• You can define other options with a map.connect
  call in config/routes.rb (see your textbook for
  details)
• Example url_for(controller gt "store",
  action gt "list")translates to
  http//your_application/store/list

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Field helpers (for models)

• Rails provides support (in the app/helpers
  directory) for HTML fields
• text_field(variable, attribute, options)
• hidden_field(variable, attribute, options)
• password_field(variable, attribute, options)
• text_area(variable, attribute, options)
• radio_button(variable, attribute, tag_value,
  options)
• check_box(variable, attribute, options,
  on_value, off_value)
• select(variable, attribute, choices, options,
  html_options)
• The first argument to a helper method is the name
  of an instance variable (typically a model
  object)
• The second argument is an attribute of that
  object
• The first and second arguments are combined (with
  an underscore) to form the id of the generated
  field
• Other arguments depend on the field type
• For text fields, the third argument is a hash of
  options, for example, size

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Field helpers (for nonmodels)

• Rails can also support fields that have no
  corresponding models
• Names end in _tag
• First argument is a simple name, not an object
• Example syntax text_field_tag(name, value
  nil, options )
• Example text_field_tag(arg1, _at_paramsarg1,
  size gt 12)
• Values will be stored in the params hash when the
  form is submitted to the controller

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Links

• The basic HTML link is lta href"URL"gt
• The basic RHTML link is lt link_to("Link
  text", action gt "method_name") gtwhere
  method_name uses the url_for() format
• The basic Ajax/RHTML link is lt
  link_to_remote( "Link text",
  update gt id_of_element_to_update,
  url gt action gt method_name ) gtwhich
  refers to ltdiv id" id_of_element_to_update
  "gtOriginal textlt/divgt

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Responding to an Ajax link

• The method_name in the link_to_remote is the name
  of a method in the controller
• Since we do not want to return a complete HTML
  page, the named method should contain at least
  the following render(layout gt false)
• Whatever is in the corresponding .rhtml will
  replace the original contents of the ltdivgt
  element

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form_remote_tag()

• To use Ajax for any form, replace form_tag and
  end_form_tag with form_remote_tag and
  end_form_tag
• All form elements will be serialized and sent to
  the server
• They can be read from the params hash

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Observers

• Observers let you call Ajax actions when the user
  changed data on a form
• Example (p. 392 in textbook)
• ltlabel for"search"gtSearch termlt/labelgtlt
  text_field_tag search gtlt observe_field(searc
  h, frequency gt 0.5,
  update gt results,
  url gt action gt
  search ) gtltdiv id"results"gtlt/divgt

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CRUD

• Basic database operations are Create, Read,
  Update, and Delete
• The scaffold method does a lot of the database
  work for you
• Scaffolds are intended to be replaced
• ActiveRecordBase provides all your basic needs
• An ActiveRecord wraps a database changes to the
  ActiveRecord result in changes to the database
• Each ActiveRecord object corresponds to a row in
  the database
• The attributes of the object correspond to the
  column in the database

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Some database methods

• new(attributes nil)
• Creates a record with the given attributes
• find(args)
• find by id
• Person.find(1) returns the object for ID 1
• find first
• Person.find(first) returns the first object
  fetched by SELECT FROM people
• find all
• Person.find(all) returns an array of objects
  for all the rows
  fetched by SELECT FROM people
• update(id, attributes)
• Creates a record with the given attributes
• destroy(id)

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References

• Agile Web Development with Rails, by Dave Thomas
  and David Hansson
• The Ajax material is from chapter 18, The Web,
  V2.0
• Some of the forms information is from chapters 16
  and 17
• Database material from chapter 14, especially
  14.5
• api.rubyonrails.com
• Database examples from ActiveRecordBase
• Some other examples from individual methods

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The End