Why not merge :joins in with_scope?

macournoyer · May 26, 2008, 5:25pm

Hi,

We’re chaining several named_scope calls like this:

Post.something_with_a_join.another_with_a_join

And we found out the :joins in the scope aren’t merged.

I’m wondering if there’s any reason why :joins aren’t merged
but :conditions and :include are, see:

rails/rails/blob/main/activerecord/lib/active_record/base.rb#L1823


      
          # frozen_string_literal: true
          
          
require "active_support/benchmarkable"
          require "active_support/dependencies"
          require "active_support/descendants_tracker"
          require "active_support/time"
          require "active_support/core_ext/class/subclasses"
          require "active_record/log_subscriber"
          require "active_record/explain_subscriber"
          require "active_record/relation/delegation"
          require "active_record/attributes"
          require "active_record/type_caster"
          require "active_record/database_configurations"
          
          
module ActiveRecord # :nodoc:
            # = Active Record
            #
            # Active Record objects don't specify their attributes directly, but rather infer them from
            # the table definition with which they're linked. Adding, removing, and changing attributes
            # and their type is done directly in the database. Any change is instantly reflected in the
            # Active Record objects. The mapping that binds a given Active Record class to a certain
            # database table will happen automatically in most common cases, but can be overwritten for the uncommon ones.
            #
            # See the mapping rules in table_name and the full example in link:files/activerecord/README_rdoc.html for more insight.
            #
            # == Creation
            #
            # Active Records accept constructor parameters either in a hash or as a block. The hash
            # method is especially useful when you're receiving the data from somewhere else, like an
            # HTTP request. It works like this:
            #
            #   user = User.new(name: "David", occupation: "Code Artist")
            #   user.name # => "David"
            #
            # You can also use block initialization:
            #
            #   user = User.new do |u|
            #     u.name = "David"
            #     u.occupation = "Code Artist"
            #   end
            #
            # And of course you can just create a bare object and specify the attributes after the fact:
            #
            #   user = User.new
            #   user.name = "David"
            #   user.occupation = "Code Artist"
            #
            # == Conditions
            #
            # Conditions can either be specified as a string, array, or hash representing the WHERE-part of an SQL statement.
            # The array form is to be used when the condition input is tainted and requires sanitization. The string form can
            # be used for statements that don't involve tainted data. The hash form works much like the array form, except
            # only equality and range is possible. Examples:
            #
            #   class User < ActiveRecord::Base
            #     def self.authenticate_unsafely(user_name, password)
            #       where("user_name = '#{user_name}' AND password = '#{password}'").first
            #     end
            #
            #     def self.authenticate_safely(user_name, password)
            #       where("user_name = ? AND password = ?", user_name, password).first
            #     end
            #
            #     def self.authenticate_safely_simply(user_name, password)
            #       where(user_name: user_name, password: password).first
            #     end
            #   end
            #
            # The <tt>authenticate_unsafely</tt> method inserts the parameters directly into the query
            # and is thus susceptible to SQL-injection attacks if the <tt>user_name</tt> and +password+
            # parameters come directly from an HTTP request. The <tt>authenticate_safely</tt> and
            # <tt>authenticate_safely_simply</tt> both will sanitize the <tt>user_name</tt> and +password+
            # before inserting them in the query, which will ensure that an attacker can't escape the
            # query and fake the login (or worse).
            #
            # When using multiple parameters in the conditions, it can easily become hard to read exactly
            # what the fourth or fifth question mark is supposed to represent. In those cases, you can
            # resort to named bind variables instead. That's done by replacing the question marks with
            # symbols and supplying a hash with values for the matching symbol keys:
            #
            #   Company.where(
            #     "id = :id AND name = :name AND division = :division AND created_at > :accounting_date",
            #     { id: 3, name: "37signals", division: "First", accounting_date: '2005-01-01' }
            #   ).first
            #
            # Similarly, a simple hash without a statement will generate conditions based on equality with the SQL AND
            # operator. For instance:
            #
            #   Student.where(first_name: "Harvey", status: 1)
            #   Student.where(params[:student])
            #
            # A range may be used in the hash to use the SQL BETWEEN operator:
            #
            #   Student.where(grade: 9..12)
            #
            # An array may be used in the hash to use the SQL IN operator:
            #
            #   Student.where(grade: [9,11,12])
            #
            # When joining tables, nested hashes or keys written in the form 'table_name.column_name'
            # can be used to qualify the table name of a particular condition. For instance:
            #
            #   Student.joins(:schools).where(schools: { category: 'public' })
            #   Student.joins(:schools).where('schools.category' => 'public' )
            #
            # == Overwriting default accessors
            #
            # All column values are automatically available through basic accessors on the Active Record
            # object, but sometimes you want to specialize this behavior. This can be done by overwriting
            # the default accessors (using the same name as the attribute) and calling
            # +super+ to actually change things.
            #
            #   class Song < ActiveRecord::Base
            #     # Uses an integer of seconds to hold the length of the song
            #
            #     def length=(minutes)
            #       super(minutes.to_i * 60)
            #     end
            #
            #     def length
            #       super / 60
            #     end
            #   end
            #
            # == Attribute query methods
            #
            # In addition to the basic accessors, query methods are also automatically available on the Active Record object.
            # Query methods allow you to test whether an attribute value is present.
            # Additionally, when dealing with numeric values, a query method will return false if the value is zero.
            #
            # For example, an Active Record User with the <tt>name</tt> attribute has a <tt>name?</tt> method that you can call
            # to determine whether the user has a name:
            #
            #   user = User.new(name: "David")
            #   user.name? # => true
            #
            #   anonymous = User.new(name: "")
            #   anonymous.name? # => false
            #
            # Query methods will also respect any overrides of default accessors:
            #
            #   class User
            #     # Has admin boolean column
            #     def admin
            #       false
            #     end
            #   end
            #
            #   user.update(admin: true)
            #
            #   user.read_attribute(:admin)  # => true, gets the column value
            #   user[:admin] # => true, also gets the column value
            #
            #   user.admin   # => false, due to the getter override
            #   user.admin?  # => false, due to the getter override
            #
            # == Accessing attributes before they have been typecasted
            #
            # Sometimes you want to be able to read the raw attribute data without having the column-determined
            # typecast run its course first. That can be done by using the <tt><attribute>_before_type_cast</tt>
            # accessors that all attributes have. For example, if your Account model has a <tt>balance</tt> attribute,
            # you can call <tt>account.balance_before_type_cast</tt> or <tt>account.id_before_type_cast</tt>.
            #
            # This is especially useful in validation situations where the user might supply a string for an
            # integer field and you want to display the original string back in an error message. Accessing the
            # attribute normally would typecast the string to 0, which isn't what you want.
            #
            # == Dynamic attribute-based finders
            #
            # Dynamic attribute-based finders are a mildly deprecated way of getting (and/or creating) objects
            # by simple queries without turning to SQL. They work by appending the name of an attribute
            # to <tt>find_by_</tt> like <tt>Person.find_by_user_name</tt>.
            # Instead of writing <tt>Person.find_by(user_name: user_name)</tt>, you can use
            # <tt>Person.find_by_user_name(user_name)</tt>.
            #
            # It's possible to add an exclamation point (!) on the end of the dynamic finders to get them to raise an
            # ActiveRecord::RecordNotFound error if they do not return any records,
            # like <tt>Person.find_by_last_name!</tt>.
            #
            # It's also possible to use multiple attributes in the same <tt>find_by_</tt> by separating them with
            # "_and_".
            #
            #  Person.find_by(user_name: user_name, password: password)
            #  Person.find_by_user_name_and_password(user_name, password) # with dynamic finder
            #
            # It's even possible to call these dynamic finder methods on relations and named scopes.
            #
            #   Payment.order("created_on").find_by_amount(50)
            #
            # == Saving arrays, hashes, and other non-mappable objects in text columns
            #
            # Active Record can serialize any object in text columns using YAML. To do so, you must
            # specify this with a call to the class method
            # {serialize}[rdoc-ref:AttributeMethods::Serialization::ClassMethods#serialize].
            # This makes it possible to store arrays, hashes, and other non-mappable objects without doing
            # any additional work.
            #
            #   class User < ActiveRecord::Base
            #     serialize :preferences
            #   end
            #
            #   user = User.create(preferences: { "background" => "black", "display" => large })
            #   User.find(user.id).preferences # => { "background" => "black", "display" => large }
            #
            # You can also specify a class option as the second parameter that'll raise an exception
            # if a serialized object is retrieved as a descendant of a class not in the hierarchy.
            #
            #   class User < ActiveRecord::Base
            #     serialize :preferences, Hash
            #   end
            #
            #   user = User.create(preferences: %w( one two three ))
            #   User.find(user.id).preferences    # raises SerializationTypeMismatch
            #
            # When you specify a class option, the default value for that attribute will be a new
            # instance of that class.
            #
            #   class User < ActiveRecord::Base
            #     serialize :preferences, OpenStruct
            #   end
            #
            #   user = User.new
            #   user.preferences.theme_color = "red"
            #
            #
            # == Single table inheritance
            #
            # Active Record allows inheritance by storing the name of the class in a
            # column that is named "type" by default. See ActiveRecord::Inheritance for
            # more details.
            #
            # == Connection to multiple databases in different models
            #
            # Connections are usually created through
            # {ActiveRecord::Base.establish_connection}[rdoc-ref:ConnectionHandling#establish_connection] and retrieved
            # by ActiveRecord::Base.connection. All classes inheriting from ActiveRecord::Base will use this
            # connection. But you can also set a class-specific connection. For example, if Course is an
            # ActiveRecord::Base, but resides in a different database, you can just say <tt>Course.establish_connection</tt>
            # and Course and all of its subclasses will use this connection instead.
            #
            # This feature is implemented by keeping a connection pool in ActiveRecord::Base that is
            # a hash indexed by the class. If a connection is requested, the
            # {ActiveRecord::Base.retrieve_connection}[rdoc-ref:ConnectionHandling#retrieve_connection] method
            # will go up the class-hierarchy until a connection is found in the connection pool.
            #
            # == Exceptions
            #
            # * ActiveRecordError - Generic error class and superclass of all other errors raised by Active Record.
            # * AdapterNotSpecified - The configuration hash used in
            #   {ActiveRecord::Base.establish_connection}[rdoc-ref:ConnectionHandling#establish_connection]
            #   didn't include an <tt>:adapter</tt> key.
            # * AdapterNotFound - The <tt>:adapter</tt> key used in
            #   {ActiveRecord::Base.establish_connection}[rdoc-ref:ConnectionHandling#establish_connection]
            #   specified a non-existent adapter
            #   (or a bad spelling of an existing one).
            # * AssociationTypeMismatch - The object assigned to the association wasn't of the type
            #   specified in the association definition.
            # * AttributeAssignmentError - An error occurred while doing a mass assignment through the
            #   {ActiveRecord::Base#attributes=}[rdoc-ref:AttributeAssignment#attributes=] method.
            #   You can inspect the +attribute+ property of the exception object to determine which attribute
            #   triggered the error.
            # * ConnectionNotEstablished - No connection has been established.
            #   Use {ActiveRecord::Base.establish_connection}[rdoc-ref:ConnectionHandling#establish_connection] before querying.
            # * MultiparameterAssignmentErrors - Collection of errors that occurred during a mass assignment using the
            #   {ActiveRecord::Base#attributes=}[rdoc-ref:AttributeAssignment#attributes=] method.
            #   The +errors+ property of this exception contains an array of
            #   AttributeAssignmentError
            #   objects that should be inspected to determine which attributes triggered the errors.
            # * RecordInvalid - raised by {ActiveRecord::Base#save!}[rdoc-ref:Persistence#save!] and
            #   {ActiveRecord::Base.create!}[rdoc-ref:Persistence::ClassMethods#create!]
            #   when the record is invalid.
            # * RecordNotFound - No record responded to the {ActiveRecord::Base.find}[rdoc-ref:FinderMethods#find] method.
            #   Either the row with the given ID doesn't exist or the row didn't meet the additional restrictions.
            #   Some {ActiveRecord::Base.find}[rdoc-ref:FinderMethods#find] calls do not raise this exception to signal
            #   nothing was found, please check its documentation for further details.
            # * SerializationTypeMismatch - The serialized object wasn't of the class specified as the second parameter.
            # * StatementInvalid - The database server rejected the SQL statement. The precise error is added in the message.
            #
            # *Note*: The attributes listed are class-level attributes (accessible from both the class and instance level).
            # So it's possible to assign a logger to the class through <tt>Base.logger=</tt> which will then be used by all
            # instances in the current object space.
            class Base
              extend ActiveModel::Naming
          
          
    extend ActiveSupport::Benchmarkable
              extend ActiveSupport::DescendantsTracker
          
          
    extend ConnectionHandling
              extend QueryCache::ClassMethods
              extend Querying
              extend Translation
              extend DynamicMatchers
              extend DelegatedType
              extend Explain
              extend Enum
              extend Delegation::DelegateCache
              extend Aggregations::ClassMethods
          
          
    include Core
              include Persistence
              include ReadonlyAttributes
              include ModelSchema
              include Inheritance
              include Scoping
              include Sanitization
              include AttributeAssignment
              include ActiveModel::Conversion
              include Integration
              include Validations
              include CounterCache
              include Attributes
              include Locking::Optimistic
              include Locking::Pessimistic
              include Encryption::EncryptableRecord
              include AttributeMethods
              include Callbacks
              include Timestamp
              include Associations
              include SecurePassword
              include AutosaveAssociation
              include NestedAttributes
              include Transactions
              include TouchLater
              include NoTouching
              include Reflection
              include Serialization
              include Store
              include SecureToken
              include TokenFor
              include SignedId
              include Suppressor
              include Normalization
              include Marshalling::Methods
            end
          
          
  ActiveSupport.run_load_hooks(:active_record, Base)
          end

This file has been truncated. show original

I know some join could be contradictory but they can also be required
by the conditions.

I have a patch ready for this but I’m waiting for some feedback before
writing some tests and submitting it, maybe I’m missing something.

Thanks,
Marc

macournoyer · May 26, 2008, 5:30pm

On 26 May 2008, at 16:24, macournoyer wrote:

but :conditions and :include are, see:
http://github.com/rails/rails/tree/master/activerecord/lib/active_record/base.rb#L1823

:joins comes in 2 forms. When :joins is like :include (ie an array of
(possibly nested) association names, i don’t see why it couldn’t
behave like :include. That usage is newish (last autumn?) so it could
jus be an omission. In the other usage where :joins is an sql fragment
then it’s rather more problematic (for doing things like removing
duplicates etc…)

Fred

macournoyer · May 26, 2008, 5:38pm

You’re right, but by not merging :joins it fails in both cases: when
it’s like include and as an sql fragment

If we merge the :joins like described here:
http://blog.teksol.info/2008/5/26/why-are-activerecord-scopes-not-merged
, it will only fail in the later case, when it’s used a an sql
fragment and both conflict.

On May 26, 11:29 am, Frederick C. [email protected]

macournoyer · May 26, 2008, 5:41pm

On 26 May 2008, at 16:34, francois.beausoleil wrote:

Shouldn’t the DB server intelligent enough to filter out duplicates in
that case ?

Doesn’t sound like the sort of thing you could rely on across the board.

macournoyer · May 26, 2008, 5:39pm

On 26 mai, 11:29, Frederick C. [email protected] wrote:

:joins comes in 2 forms. When :joins is like :include (ie an array of
(possibly nested) association names, i don’t see why it couldn’t
behave like :include. That usage is newish (last autumn?) so it could
jus be an omission. In the other usage where :joins is an sql fragment
then it’s rather more problematic (for doing things like removing
duplicates etc…)

Shouldn’t the DB server intelligent enough to filter out duplicates in
that case ?

Thanks!
François

macournoyer · May 26, 2008, 5:44pm

On 26 May 2008, at 16:37, macournoyer wrote:

You’re right, but by not merging :joins it fails in both cases: when
it’s like include and as an sql fragment

If we merge the :joins like described here:
http://blog.teksol.info/2008/5/26/why-are-activerecord-scopes-not-merged
, it will only fail in the later case, when it’s used a an sql
fragment and both conflict.

I think you’d probably want to base yourself on what :include does (in
fact you could probably reuse the merge_includes code), as you need to
handle the fact that you can say :joins => :foo or :joins => [:foo]
and things like that

Fred

macournoyer · May 26, 2008, 7:24pm

Hey,

I’m probably the last person to touch the :joins => :association style
syntax so I’d like to chime in with a warning here. The change
proposed in:

http://blog.teksol.info/2008/5/26/why-are-activerecord-scopes-not-merged

sets off alarm bells for me. See the following line:

github.com

rails/rails/blob/main/activerecord/lib/active_record/base.rb#L1552


      
          # frozen_string_literal: true
          
          
require "active_support/benchmarkable"
          require "active_support/dependencies"
          require "active_support/descendants_tracker"
          require "active_support/time"
          require "active_support/core_ext/class/subclasses"
          require "active_record/log_subscriber"
          require "active_record/explain_subscriber"
          require "active_record/relation/delegation"
          require "active_record/attributes"
          require "active_record/type_caster"
          require "active_record/database_configurations"
          
          
module ActiveRecord # :nodoc:
            # = Active Record
            #
            # Active Record objects don't specify their attributes directly, but rather infer them from
            # the table definition with which they're linked. Adding, removing, and changing attributes
            # and their type is done directly in the database. Any change is instantly reflected in the
            # Active Record objects. The mapping that binds a given Active Record class to a certain
            # database table will happen automatically in most common cases, but can be overwritten for the uncommon ones.
            #
            # See the mapping rules in table_name and the full example in link:files/activerecord/README_rdoc.html for more insight.
            #
            # == Creation
            #
            # Active Records accept constructor parameters either in a hash or as a block. The hash
            # method is especially useful when you're receiving the data from somewhere else, like an
            # HTTP request. It works like this:
            #
            #   user = User.new(name: "David", occupation: "Code Artist")
            #   user.name # => "David"
            #
            # You can also use block initialization:
            #
            #   user = User.new do |u|
            #     u.name = "David"
            #     u.occupation = "Code Artist"
            #   end
            #
            # And of course you can just create a bare object and specify the attributes after the fact:
            #
            #   user = User.new
            #   user.name = "David"
            #   user.occupation = "Code Artist"
            #
            # == Conditions
            #
            # Conditions can either be specified as a string, array, or hash representing the WHERE-part of an SQL statement.
            # The array form is to be used when the condition input is tainted and requires sanitization. The string form can
            # be used for statements that don't involve tainted data. The hash form works much like the array form, except
            # only equality and range is possible. Examples:
            #
            #   class User < ActiveRecord::Base
            #     def self.authenticate_unsafely(user_name, password)
            #       where("user_name = '#{user_name}' AND password = '#{password}'").first
            #     end
            #
            #     def self.authenticate_safely(user_name, password)
            #       where("user_name = ? AND password = ?", user_name, password).first
            #     end
            #
            #     def self.authenticate_safely_simply(user_name, password)
            #       where(user_name: user_name, password: password).first
            #     end
            #   end
            #
            # The <tt>authenticate_unsafely</tt> method inserts the parameters directly into the query
            # and is thus susceptible to SQL-injection attacks if the <tt>user_name</tt> and +password+
            # parameters come directly from an HTTP request. The <tt>authenticate_safely</tt> and
            # <tt>authenticate_safely_simply</tt> both will sanitize the <tt>user_name</tt> and +password+
            # before inserting them in the query, which will ensure that an attacker can't escape the
            # query and fake the login (or worse).
            #
            # When using multiple parameters in the conditions, it can easily become hard to read exactly
            # what the fourth or fifth question mark is supposed to represent. In those cases, you can
            # resort to named bind variables instead. That's done by replacing the question marks with
            # symbols and supplying a hash with values for the matching symbol keys:
            #
            #   Company.where(
            #     "id = :id AND name = :name AND division = :division AND created_at > :accounting_date",
            #     { id: 3, name: "37signals", division: "First", accounting_date: '2005-01-01' }
            #   ).first
            #
            # Similarly, a simple hash without a statement will generate conditions based on equality with the SQL AND
            # operator. For instance:
            #
            #   Student.where(first_name: "Harvey", status: 1)
            #   Student.where(params[:student])
            #
            # A range may be used in the hash to use the SQL BETWEEN operator:
            #
            #   Student.where(grade: 9..12)
            #
            # An array may be used in the hash to use the SQL IN operator:
            #
            #   Student.where(grade: [9,11,12])
            #
            # When joining tables, nested hashes or keys written in the form 'table_name.column_name'
            # can be used to qualify the table name of a particular condition. For instance:
            #
            #   Student.joins(:schools).where(schools: { category: 'public' })
            #   Student.joins(:schools).where('schools.category' => 'public' )
            #
            # == Overwriting default accessors
            #
            # All column values are automatically available through basic accessors on the Active Record
            # object, but sometimes you want to specialize this behavior. This can be done by overwriting
            # the default accessors (using the same name as the attribute) and calling
            # +super+ to actually change things.
            #
            #   class Song < ActiveRecord::Base
            #     # Uses an integer of seconds to hold the length of the song
            #
            #     def length=(minutes)
            #       super(minutes.to_i * 60)
            #     end
            #
            #     def length
            #       super / 60
            #     end
            #   end
            #
            # == Attribute query methods
            #
            # In addition to the basic accessors, query methods are also automatically available on the Active Record object.
            # Query methods allow you to test whether an attribute value is present.
            # Additionally, when dealing with numeric values, a query method will return false if the value is zero.
            #
            # For example, an Active Record User with the <tt>name</tt> attribute has a <tt>name?</tt> method that you can call
            # to determine whether the user has a name:
            #
            #   user = User.new(name: "David")
            #   user.name? # => true
            #
            #   anonymous = User.new(name: "")
            #   anonymous.name? # => false
            #
            # Query methods will also respect any overrides of default accessors:
            #
            #   class User
            #     # Has admin boolean column
            #     def admin
            #       false
            #     end
            #   end
            #
            #   user.update(admin: true)
            #
            #   user.read_attribute(:admin)  # => true, gets the column value
            #   user[:admin] # => true, also gets the column value
            #
            #   user.admin   # => false, due to the getter override
            #   user.admin?  # => false, due to the getter override
            #
            # == Accessing attributes before they have been typecasted
            #
            # Sometimes you want to be able to read the raw attribute data without having the column-determined
            # typecast run its course first. That can be done by using the <tt><attribute>_before_type_cast</tt>
            # accessors that all attributes have. For example, if your Account model has a <tt>balance</tt> attribute,
            # you can call <tt>account.balance_before_type_cast</tt> or <tt>account.id_before_type_cast</tt>.
            #
            # This is especially useful in validation situations where the user might supply a string for an
            # integer field and you want to display the original string back in an error message. Accessing the
            # attribute normally would typecast the string to 0, which isn't what you want.
            #
            # == Dynamic attribute-based finders
            #
            # Dynamic attribute-based finders are a mildly deprecated way of getting (and/or creating) objects
            # by simple queries without turning to SQL. They work by appending the name of an attribute
            # to <tt>find_by_</tt> like <tt>Person.find_by_user_name</tt>.
            # Instead of writing <tt>Person.find_by(user_name: user_name)</tt>, you can use
            # <tt>Person.find_by_user_name(user_name)</tt>.
            #
            # It's possible to add an exclamation point (!) on the end of the dynamic finders to get them to raise an
            # ActiveRecord::RecordNotFound error if they do not return any records,
            # like <tt>Person.find_by_last_name!</tt>.
            #
            # It's also possible to use multiple attributes in the same <tt>find_by_</tt> by separating them with
            # "_and_".
            #
            #  Person.find_by(user_name: user_name, password: password)
            #  Person.find_by_user_name_and_password(user_name, password) # with dynamic finder
            #
            # It's even possible to call these dynamic finder methods on relations and named scopes.
            #
            #   Payment.order("created_on").find_by_amount(50)
            #
            # == Saving arrays, hashes, and other non-mappable objects in text columns
            #
            # Active Record can serialize any object in text columns using YAML. To do so, you must
            # specify this with a call to the class method
            # {serialize}[rdoc-ref:AttributeMethods::Serialization::ClassMethods#serialize].
            # This makes it possible to store arrays, hashes, and other non-mappable objects without doing
            # any additional work.
            #
            #   class User < ActiveRecord::Base
            #     serialize :preferences
            #   end
            #
            #   user = User.create(preferences: { "background" => "black", "display" => large })
            #   User.find(user.id).preferences # => { "background" => "black", "display" => large }
            #
            # You can also specify a class option as the second parameter that'll raise an exception
            # if a serialized object is retrieved as a descendant of a class not in the hierarchy.
            #
            #   class User < ActiveRecord::Base
            #     serialize :preferences, Hash
            #   end
            #
            #   user = User.create(preferences: %w( one two three ))
            #   User.find(user.id).preferences    # raises SerializationTypeMismatch
            #
            # When you specify a class option, the default value for that attribute will be a new
            # instance of that class.
            #
            #   class User < ActiveRecord::Base
            #     serialize :preferences, OpenStruct
            #   end
            #
            #   user = User.new
            #   user.preferences.theme_color = "red"
            #
            #
            # == Single table inheritance
            #
            # Active Record allows inheritance by storing the name of the class in a
            # column that is named "type" by default. See ActiveRecord::Inheritance for
            # more details.
            #
            # == Connection to multiple databases in different models
            #
            # Connections are usually created through
            # {ActiveRecord::Base.establish_connection}[rdoc-ref:ConnectionHandling#establish_connection] and retrieved
            # by ActiveRecord::Base.connection. All classes inheriting from ActiveRecord::Base will use this
            # connection. But you can also set a class-specific connection. For example, if Course is an
            # ActiveRecord::Base, but resides in a different database, you can just say <tt>Course.establish_connection</tt>
            # and Course and all of its subclasses will use this connection instead.
            #
            # This feature is implemented by keeping a connection pool in ActiveRecord::Base that is
            # a hash indexed by the class. If a connection is requested, the
            # {ActiveRecord::Base.retrieve_connection}[rdoc-ref:ConnectionHandling#retrieve_connection] method
            # will go up the class-hierarchy until a connection is found in the connection pool.
            #
            # == Exceptions
            #
            # * ActiveRecordError - Generic error class and superclass of all other errors raised by Active Record.
            # * AdapterNotSpecified - The configuration hash used in
            #   {ActiveRecord::Base.establish_connection}[rdoc-ref:ConnectionHandling#establish_connection]
            #   didn't include an <tt>:adapter</tt> key.
            # * AdapterNotFound - The <tt>:adapter</tt> key used in
            #   {ActiveRecord::Base.establish_connection}[rdoc-ref:ConnectionHandling#establish_connection]
            #   specified a non-existent adapter
            #   (or a bad spelling of an existing one).
            # * AssociationTypeMismatch - The object assigned to the association wasn't of the type
            #   specified in the association definition.
            # * AttributeAssignmentError - An error occurred while doing a mass assignment through the
            #   {ActiveRecord::Base#attributes=}[rdoc-ref:AttributeAssignment#attributes=] method.
            #   You can inspect the +attribute+ property of the exception object to determine which attribute
            #   triggered the error.
            # * ConnectionNotEstablished - No connection has been established.
            #   Use {ActiveRecord::Base.establish_connection}[rdoc-ref:ConnectionHandling#establish_connection] before querying.
            # * MultiparameterAssignmentErrors - Collection of errors that occurred during a mass assignment using the
            #   {ActiveRecord::Base#attributes=}[rdoc-ref:AttributeAssignment#attributes=] method.
            #   The +errors+ property of this exception contains an array of
            #   AttributeAssignmentError
            #   objects that should be inspected to determine which attributes triggered the errors.
            # * RecordInvalid - raised by {ActiveRecord::Base#save!}[rdoc-ref:Persistence#save!] and
            #   {ActiveRecord::Base.create!}[rdoc-ref:Persistence::ClassMethods#create!]
            #   when the record is invalid.
            # * RecordNotFound - No record responded to the {ActiveRecord::Base.find}[rdoc-ref:FinderMethods#find] method.
            #   Either the row with the given ID doesn't exist or the row didn't meet the additional restrictions.
            #   Some {ActiveRecord::Base.find}[rdoc-ref:FinderMethods#find] calls do not raise this exception to signal
            #   nothing was found, please check its documentation for further details.
            # * SerializationTypeMismatch - The serialized object wasn't of the class specified as the second parameter.
            # * StatementInvalid - The database server rejected the SQL statement. The precise error is added in the message.
            #
            # *Note*: The attributes listed are class-level attributes (accessible from both the class and instance level).
            # So it's possible to assign a logger to the class through <tt>Base.logger=</tt> which will then be used by all
            # instances in the current object space.
            class Base
              extend ActiveModel::Naming
          
          
    extend ActiveSupport::Benchmarkable
              extend ActiveSupport::DescendantsTracker
          
          
    extend ConnectionHandling
              extend QueryCache::ClassMethods
              extend Querying
              extend Translation
              extend DynamicMatchers
              extend DelegatedType
              extend Explain
              extend Enum
              extend Delegation::DelegateCache
              extend Aggregations::ClassMethods
          
          
    include Core
              include Persistence
              include ReadonlyAttributes
              include ModelSchema
              include Inheritance
              include Scoping
              include Sanitization
              include AttributeAssignment
              include ActiveModel::Conversion
              include Integration
              include Validations
              include CounterCache
              include Attributes
              include Locking::Optimistic
              include Locking::Pessimistic
              include Encryption::EncryptableRecord
              include AttributeMethods
              include Callbacks
              include Timestamp
              include Associations
              include SecurePassword
              include AutosaveAssociation
              include NestedAttributes
              include Transactions
              include TouchLater
              include NoTouching
              include Reflection
              include Serialization
              include Store
              include SecureToken
              include TokenFor
              include SignedId
              include Suppressor
              include Normalization
              include Marshalling::Methods
            end
          
          
  ActiveSupport.run_load_hooks(:active_record, Base)
          end

This file has been truncated. show original

What that line does is ensure that your joins {:like => :this}, :or,
[:like, :this] will be treated as an inner join. If you just
concatenate the :joins together into a string you’ll break those
semantics.

I know Fred has already brought it to your attention that you should
base your code off the way that :includes are handled (merge_includes)
but I just wanted to add some weight to that.

And as for “why doesn’t it already do what it ought to?”… I’m pretty
sure that when I reworked that stuff I didn’t actually remove
anything so I kind of hope it never merged joins in scopes in the
first place… if I did remove something critical then I shall quietly
flog myself

Regards,
Trevor

On 5/26/08, Frederick C. [email protected] wrote:

, it will only fail in the later case, when it’s used a an sql

(possibly nested) association names, i don’t see why it couldn’t

by the conditions.

–

Trevor S.
http://somethinglearned.com