LHS

LHS uses LHC for http requests.

Very Short Introduction

Access data that is provided by an http json service with ease using a LHS::Record.

class Record < LHS::Record

  endpoint ':service/v2/records'
  endpoint ':service/v2/association/:association_id/records'

end

record = Record.find_by(email: '[email protected]') #<Record>
record.review # "Lunch was great"

Where to store LHS::Records

Please store all defined LHS::Records in app/models as they are not autoloaded by rails otherwise.

Endpoints

You setup a LHS::Record by configuring one or multiple endpoints. You can also add request options for an endpoint (see following example).

class Record < LHS::Record

  endpoint ':service/v2/association/:association_id/records'
  endpoint ':service/v2/association/:association_id/records/:id'
  endpoint ':service/v2/records', cache: true, cache_expires_in: 1.day
  endpoint ':service/v2/records/:id', cache: true, cache_expires_in: 1.day

end

Please use placeholders when configuring endpoints also for hosts. Otherwise LHS will match them strictly, which can result in problems when mixing URLs containing http, https or no protocol at all. https://github.com/local-ch/lhc/blob/master/docs/configuration.md#placeholders

If you try to setup a LHS::Record with clashing endpoints it will immediately raise an exception.

class Record < LHS::Record

  endpoint ':service/v2/records'
  endpoint ':service/v2/something_else'

end
# raises: Clashing endpoints.

Find multiple records

You can query a service for records by using where.

  Record.where(color: 'blue')

This uses the :service/v2/records endpoint, cause :association_id was not provided. In addition it would add ?color=blue to the get parameters.

  Record.where(association_id: 'fq-a81ngsl1d')

Uses the :service/v2/association/:association_id/records endpoint.

Chaining where statements

LHS supports chaining where statements. That allows you to chain multiple where-queries:

class Record < LHS::Record
  endpoint 'records/'
  endpoint 'records/:id'
end

records = Record.where(color: 'blue')
...
records.where(available: true).each do |record|
  ...
end

The example would fetch records with the following parameters: {color: blue, available: true}.

Where values hash

Returns a hash of where conditions. Common to use in tests, as where queries are not performing any HTTP-requests when no data is accessed.

records = Record.where(color: 'blue').where(available: true).where(color: 'red')

expect(
  records
).to have_requested(:get, %r{records/})
  .with(query: hash_including(color: 'blue', available: true))
# will fail as no http request is made (no data requested)

expect(
  records.where_values_hash
).to eq {color: 'red', available: true}

Scopes: Reuse where statements

In order to make common where statements reusable you can organise them in scopes:

class Record < LHS::Record
  endpoint 'records/'
  endpoint 'records/:id'
  scope :blue, -> { where(color: 'blue') }
  scope :available, ->(state) { where(available: state) }
end

records = Record.blue.available(true)
The example would fetch records with the following parameters: `{color: blue, visible: true}`.

Error handling with chains

One benefit of chains is lazy evaluation. This means they get resolved when data is accessed. This makes it hard to catch errors with normal rescue blocks.

To simplify error handling with chains, you can also chain error handlers to be resolved, as part of the chain.

In case no matchin error handler is found the error gets re-raised.

record = Record.where(color: 'blue')
  .handle(LHC::BadRequest, ->(error){ show_error })
  .handle(LHC::Unauthorized, ->(error){ authorize })

List of possible error classes

Find single records

find finds a unique record by uniqe identifier (usualy id).

If no record is found an error is raised.

find can also be used to find a single uniqe record with parameters:

  Record.find(association_id: 123, id: 456)

find_by finds the first record matching the specified conditions.

If no record is found, nil is returned.

find_by! raises LHC::NotFound if nothing was found.

  Record.find_by(id: 'z12f-3asm3ngals')
  Record.find_by(id: 'doesntexist') # nil

first is an alias for finding the first record without parameters.

  Record.first

If no record is found, nil is returned.

first! raises LHC::NotFound if nothing was found.

Find multiple single records in parallel

In case you want to fetch multiple records by id in parallel, you can also do this with find:

Record.find(1, 2, 3)

If you want to inject values for the failing records, that might not have been found, you can inject values for them with error handlers:

data = Record
  .handle(LHC::Unauthorized, ->(response) { Record.new(name: 'unknown') })
  .find(1, 2, 3)
data[1].name # 'unknown'

Navigate data

After fetching single or multiple records you can navigate the received data with ease.

  records = Record.where(color: 'blue')
  records.collection? # true
  record = records.first
  record.item? # true
  record.parent == records # true

Request based options

You can apply options to the request chain. Those options will be forwarded to the request perfomed by the chain/query.

  # Authenticate with OAuth
  options = { auth: { bearer: '123456' } }

  AuthenticatedRecord = Record.options(options)

  blue_records = AuthenticatedRecord.where(color: 'blue')
  active_records = AuthenticatedRecord.where(active: true)

  AuthenticatedRecord.create(color: 'red')

  record = AuthenticatedRecord.find(123)
  # Find resolves the current query and applies all options from the chain
  # All further requests are made from scratch and not based on the previous options
  record.name = 'Walter'

  authenticated_record = record.options(options)
  authenticated_record.valid?
  authenticated_record.save
  authenticated_record.destroy
  authenticated_record.update(name: 'Steve')

Batch processing

Be careful using methods for batch processing. They could result in a lot of HTTP requests!

all fetches all records from the service by doing multiple requests if necessary.

data = Record.all
data.count # 998
data.length # 998

Count vs. Length

find_each is a more fine grained way to process single records that are fetched in batches.

Record.find_each(start: 50, batch_size: 20, params: { has_reviews: true }) do |record|
  # Iterates over each record. Starts with record nr. 50 and fetches 20 records each batch.
  record
  break if record.some_attribute == some_value
end

find_in_batches is used by find_each and processes batches.

Record.find_in_batches(start: 50, batch_size: 20, params: { has_reviews: true }) do |records|
  # Iterates over multiple records (batch size is 20). Starts with record nr. 50 and fetches 20 records each batch.
  records
  break if records.first.name == some_value
end

Create records

  record = Record.create(
    recommended: true,
    source_id: 'aaa',
    content_ad_id: '1z-5r1fkaj'
  )

When creation fails, the object contains errors. It provides them through the errors attribute:

  record.errors #<LHS::Errors>
  record.errors.include?(:ratings) # true
  record.errors[:ratings] # ['REQUIRED_PROPERTY_VALUE']
  record.errors.messages # {:ratings=>["REQUIRED_PROPERTY_VALUE"], :recommended=>["REQUIRED_PROPERTY_VALUE"]}
  record.errors.message # ratings must be set when review or name or review_title is set | The property value is required; it cannot be null, empty, or blank."

Create records through associations (nested resources)

  class Review < LHS::Record
    endpoint ':service/reviews'
  end 

  class Comment < LHS::Record
    endpoint ':service/reviews/:review_id/comments'
  end

Item

  review = Review.find(1)
  # Review#1
  # :href => ':service/reviews/1
  # :text => 'Simply awesome'
  # :comment => { :href => ':service/reviews/1/comments }

  review.comment.create(text: 'Thank you!')
  # Comment#1
  # :href => ':service/reviews/1/comments
  # :text => 'Thank you!'

  review
  # Review#1
  # :href => ':service/reviews/1
  # :text => 'Simply awesome'
  # :comment => { :href => ':service/reviews/1/comments, :text => 'Thank you!' }

If the item already exists ArgumentError is raised.

Expanded collection

  review = Review.includes(:comments).find(1)
  # Review#1
  # :href => ':service/reviews/1'
  # :text => 'Simply awesome'
  # :comments => { :href => ':service/reviews/1/comments, :items => [] }

  review.comments.create(text: 'Thank you!')
  # Comment#1
  # :href => ':service/reviews/1/comments/1'
  # :text => 'Thank you!'

  review
  # Review#1
  # :href => ':service/reviews/1'
  # :text => 'Simply awesome'
  # :comments => { :href => ':service/reviews/1/comments, :items => [{ :href => ':service/reviews/1/comments/1', :text => 'Thank you!' }] }

Not expanded collection

  review = Review.find(1)
  # Review#1
  # :href => ':service/reviews/1'
  # :text => 'Simply awesome'
  # :comments => { :href => ':service/reviews/1/comments' }

  review.comments.create(text: 'Thank you!')
  # Comment#1
  # :href => ':service/reviews/1/comments/1'
  # :text => 'Thank you!'

  review
  # Review#1
  # :href => ':service/reviews/1
  # :text => 'Simply awesome'
  # :comments => { :href => ':service/reviews/1/comments', :items => [{ :href => ':service/reviews/1/comments/1', :text => 'Thank you!' }] }

Build new records

Build and persist new items from scratch are done either with new or it's alias build.

  record = Record.new(recommended: true)
  record.save

Custom setters and getters

Sometimes it is the case that you want to have your custom getters and setters and convert the data to a processable format behind the scenes. The initializer will now use custom setter if one is defined:


module RatingsConversions
  def ratings=(values)
    super(
      values.map { |k, v| { name: k, value: v } }
    )
  end
end

class Record < LHS::Record
  prepend RatingsConversions
end

record = Record.new(ratings: { quality: 3 })
record.ratings # [{ :name=>:quality, :value=>3 }]

If you have an accompanying getter the whole data manipulation would be internal only.

module RatingsConversions
  def ratings=(values)
    super(
      values.map { |k, v| { name: k, value: v } }
    )
  end

  def ratings
    super.map { |r| [r[:name], r[:value]] }]
  end
end

class Record < LHS::Record
  prepend RatingsConversions
end

record = Record.new(ratings: { quality: 3 }) # [{ :name=>:quality, :value=>3 }]
record.ratings # {:quality=>3}

Include linked resources

When fetching records, you can specify in advance all the linked resources that you want to include in the results. With includes, LHS ensures that all matching and explicitly linked resources are loaded and merged, if they're included in the server response.

The implementation is heavily influenced by http://guides.rubyonrails.org/active_record_class_querying and you should read it to understand this feature in all its glory.

One-Level `includes`

  # a claim has a localch_account
  claims = Claims.includes(:localch_account).where(place_id: 'huU90mB_6vAfUdVz_uDoyA')
  claims.first.localch_account.email # '[email protected]'

Before include:

{
  "href" : "http://datastore/v2/places/huU90mB_6vAfUdVz_uDoyA/claims",
  "items" : [
    {
      "href" : "http://datastore/v2/localch-accounts/6bSss0y93lK0MrVsgdNNdg/claims/huU90mB_6vAfUdVz_uDoyA",
      "localch_account" : {
        "href" : "http://datastore/v2/localch-accounts/6bSss0y93lK0MrVsgdNNdg"
      }
    }
  ]
}

After include:

{
  "href" : "http://datastore/v2/places/huU90mB_6vAfUdVz_uDoyA/claims",
  "items" : [
    {
      "href" : "http://datastore/v2/localch-accounts/6bSss0y93lK0MrVsgdNNdg/claims/huU90mB_6vAfUdVz_uDoyA",
      "localch_account" : {
        "href" : "http://datastore/v2/localch-accounts/6bSss0y93lK0MrVsgdNNdg",
        "id" : "6bSss0y93lK0MrVsgdNNdg",
        "name" : "Myriam",
        "phone" : "12345678",
        "email" : "[email protected]"
      }
    }
  ]
}

Two-Level `includes`

  # a record has a association, which has an entry
  records = Record.includes(association: :entry).where(has_reviews: true)
  records.first.association.entry.name # 'Casa Ferlin'

Multiple `includes`

  # list of includes
  claims = Claims.includes(:localch_account, :entry).where(place_id: 'huU90mB_6vAfUdVz_uDoyA')

  # array of includes
  claims = Claims.includes([:localch_account, :entry]).where(place_id: 'huU90mB_6vAfUdVz_uDoyA')

  # Two-level with array of includes
  records = Record.includes(campaign: [:entry, :user]).where(has_reviews: true)

Known LHS::Records are used to request linked resources

When including linked resources with includes, known/defined services and endpoints are used to make those requests. That also means that options for endpoints of linked resources are applied when requesting those in addition. This allows you to include protected resources (e.g. Basic auth) as endpoint options for oauth authentication get applied.

The Auth Inteceptor from lhc-core-interceptors is used to configure the following endpoints.

class Favorite < LHS::Record

  endpoint ':service/:user_id/favorites', auth: { basic: { username: 'steve', password: 'can' } }
  endpoint ':service/:user_id/favorites/:id', auth: { basic: { username: 'steve', password: 'can' } }

end

class Place < LHS::Record

  endpoint ':service/v2/places', auth: { basic: { username: 'steve', password: 'can' } }
  endpoint ':service/v2/places/:id', auth: { basic: { username: 'steve', password: 'can' } }

end

Favorite.includes(:place).where(user_id: current_user.id)
# Will include places and applies endpoint options to authenticate the request.

Forward options used for request made to include referenced resources

Provide options to the requests made to include referenced resources:


  Favorite.includes(:place).references(place: { auth: { bearer: '123' }})

Map data

To influence how data is accessed/provied, you can use mappings to either map deep nested data or to manipulate data when its accessed. Simply create methods inside the LHS::Record. They can access underlying data:

class LocalEntry < LHS::Record
  endpoint ':service/v2/local-entries'

  def name
    addresses.first.business.identities.first.name
  end

end

Nested records

Nested records (in nested data) are automaticaly casted when the href matches any defined endpoint of any LHS::Record.

class Place < LHS::Record
  endpoint ':service/v2/places'

  def name
    addresses.first.business.identities.first.name
  end
end

class Favorite < LHS::Record
  endpoint ':service/v2/favorites'
end

favorite = Favorite.includes(:place).find(1)
favorite.place.name # local.ch AG

If automatic-detection of nested records does not work, make sure your LHS::Records are stored in app/models!

Setters

You can change attributes of LHS::Records:

  record = Record.find(id: 'z12f-3asm3ngals')
  rcord.recommended = false

Save

You can persist changes with save. save will return false if persisting fails. save! instead will raise an exception.

  record = Record.find('1z-5r1fkaj')
  record.recommended = false
  record.save

Update

update will return false if persisting fails. update! instead will an raise exception.

update always updates the data of the local object first, before it tries to sync with an endpoint. So even if persisting fails, the local object is updated.

record = Record.find('1z-5r1fkaj')
record.update(recommended: false)

Destroy

You can delete records remotely by calling destroy on an LHS::Record.

  record = Record.find('1z-5r1fkaj')
  record.destroy

You can also destroy records directly without fetching them first:

  destroyed_record = Record.destroy('1z-5r1fkaj')

or with parameters:

  destroyed_records = Record.destroy(name: 'Steve')

Validation

In order to validate LHS::Records before persisting them, you can use the valid? (validate alias) method.

The specific endpoint has to support validations without peristance. An endpoint has to be enabled (opt-in) for validations in the service configuration.

class User < LHS::Record
  endpoint ':service/v2/users', validates: { params: { persist: false } }
end

user = User.build(email: 'im not an email address')
unless user.valid?
  fail(user.errors[:email])
end

The parameters passed to the validates endpoint option are used to perform the validation:

  endpoint ':service/v2/users', validates: { params: { persist: false } }  # will add ?persist=false to the request
  endpoint ':service/v2/users', validates: { params: { publish: false } }  # will add ?publish=false to the request
  endpoint ':service/v2/users', validates: { params: { validates: true } } # will add ?validates=true to the request
  endpoint ':service/v2/users', validates: { path: 'validate' }            # will perform a validation via :service/v2/users/validate

Custom validation errors

In case you want to add custom validation errors to an instance of LHS::Record:

user.errors.add(:name, 'The name you provided is not valid.')

Know issue with `ActiveModel::Validations`

If you are using ActiveModel::Validations and add errors to the LHS::Record instance - as described above - then those errors will be overwritten by the errors from ActiveModel::Validations when using save or valid?. Open issue

Pagination

LHS supports paginated APIs and it also supports various pagination strategies and by providing configuration possibilities.

LHS diffentiates between the pagination strategy (how items/pages are navigated) itself and pagination keys (how stuff is named).

Example 1 "offset"-strategy (default configuration)

# API response
{
  items: [{...}, ...]
  total: 300,
  limit: 100,
  offset: 0
}
# Next 'pages' are navigated with offset: 100, offset: 200, ...

# Nothing has to be configured in LHS because this is default pagination naming and strategy
class Results < LHS::Record
  endpoint 'results'
end

Example 2 "page"-strategy and some naming configuration

# API response
{
  docs: [{...}, ...]
  totalPages: 3,
  limit: 100,
  page: 1
}
# Next 'pages' are navigated with page: 1, offset: 2, ...

# How LHS has to be configured
class Results < LHS::Record
  configuration items_key: 'docs', total_key: 'totalPages', pagination_key: 'page', pagination_strategy: 'page'
  endpoint 'results'
end

Example 3 "start"-strategy and naming configuration

# API response
{
  results: [{...}, ...]
  total: 300,
  badgeSize: 100,
  startAt: 1
}
# Next 'pages' are navigated with startWith: 101, startWith: 201, ...

# How LHS has to be configured
class Results < LHS::Record
  configuration items_key: 'results', limit_key: 'badgeSize', pagination_key: 'startAt', pagination_strategy: 'start'
  endpoint 'results'
end

items_key key used to determine items of the current page (e.g. docs, items, etc.).

limit_key key used to work with page limits (e.g. size, limit, etc.)

pagination_key key used to paginate multiple pages (e.g. offset, page, startAt etc.).

pagination_strategy used to configure the strategy used for navigating (e.g. offset, page, start, etc.).

total_key key used to determine the total amount of items (e.g. total, totalResults, etc.).

In case of paginated resources it's important to know the difference between count vs. length

Pagination Chains

You can use chainable pagination in combination with query chains:

  class Record < LHS::Record
    endpoint ':service/records'
  end
  Record.page(3).per(20).where(color: 'blue')
  # /records?offset=40&limit=20&color=blue

The applied pagination strategy depends on the actual configured pagination, so the interface is the same for all strategies:

  class Record < LHS::Record
    endpoint ':service/records'
    configuration pagination_strategy: 'page'
  end
  Record.page(3).per(20).where(color: 'blue')
  # /records?page=3&limit=20&color=blue

  class Record < LHS::Record
    endpoint ':service/records'
    configuration pagination_strategy: 'start'
  end
  Record.page(3).per(20).where(color: 'blue')
  # /records?start=41&limit=20&color=blue

limit(argument) is an alias for per(argument). Take notice that limit without argument instead, makes the query resolve and provides the current limit from the responds.

Partial Kaminari support

LHS implements an interface that makes it partially working with Kaminari.

The kaminari’s page parameter is in params[:page]. For example, you can use kaminari to render paginations based on LHS Records. Typically, your code will look like this:

# controller
@items = Record.page(params[:page]).per(100)

# view
= paginate @items

Automatic Detection of Collections

How to configure endpoints for automatic collection detection?

LHS detects autmatically if the responded data is a single business object or a set of business objects (collection).

Conventionally, when the responds contains an items key { items: [] } it's treated as a collection, but also if the responds contains a plain raw array: [{ href: '' }] it's also treated as a collection.

In case the responds uses another key than items, you can configure it within an LHS::Record:

class Results < LHS::Record
  configuration items_key: 'docs'
end

form_for Helper

Rails form_for view-helper can be used in combination with instances of LHS::Record to autogenerate forms:

<%= form_for(@instance, url: '/create') do |f| %>
  <%= f.text_field :name %>
  <%= f.text_area :text %>
  <%= f.submit "Create" %>
<% end %>

Count vs. Length

The behaviour of count and length is based on ActiveRecord's behaviour.

count Determine the number of elements by taking the number of total elements that is provided by the endpoint/api.

length This returns the number of elements loaded from an endpoint/api. In case of paginated resources this can be different to count, as it depends on how many pages have been loaded.

Inheritance

You can inherit from previously defined records and also inherit endpoints that way:

class Base < LHS::Record
  endpoint 'records/:id'
end

class Example < Base
end

Example.find(1) # GET records/1

License

GNU Affero General Public License Version 3.

LHS

Very Short Introduction

Where to store LHS::Records

Endpoints

Find multiple records

Chaining where statements

Where values hash

Scopes: Reuse where statements

Error handling with chains

Find single records

Find multiple single records in parallel

Navigate data

Request based options

Batch processing

Create records

Create records through associations (nested resources)

Item

Expanded collection

Not expanded collection

Build new records

Custom setters and getters

Include linked resources

One-Level includes

Two-Level includes

Multiple includes

Known LHS::Records are used to request linked resources

Forward options used for request made to include referenced resources

Map data

Nested records

Setters

Save

Update

Destroy

Validation

Custom validation errors

Know issue with ActiveModel::Validations

Pagination

Pagination Chains

Partial Kaminari support

Automatic Detection of Collections

form_for Helper

Count vs. Length

Inheritance

License

One-Level `includes`

Two-Level `includes`

Multiple `includes`

Know issue with `ActiveModel::Validations`