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diff --git a/guides/source/association_basics.md b/guides/source/association_basics.md index 16a5241319..df38bd7321 100644 --- a/guides/source/association_basics.md +++ b/guides/source/association_basics.md @@ -40,7 +40,7 @@ end @customer.destroy ``` -With Active Record associations, we can streamline these — and other — operations by declaratively telling Rails that there is a connection between the two models. Here's the revised code for setting up customers and orders: +With Active Record associations, we can streamline these - and other - operations by declaratively telling Rails that there is a connection between the two models. Here's the revised code for setting up customers and orders: ```ruby class Customer < ActiveRecord::Base @@ -69,7 +69,7 @@ To learn more about the different types of associations, read the next section o The Types of Associations ------------------------- -In Rails, an _association_ is a connection between two Active Record models. Associations are implemented using macro-style calls, so that you can declaratively add features to your models. For example, by declaring that one model `belongs_to` another, you instruct Rails to maintain Primary Key–Foreign Key information between instances of the two models, and you also get a number of utility methods added to your model. Rails supports six types of associations: +In Rails, an _association_ is a connection between two Active Record models. Associations are implemented using macro-style calls, so that you can declaratively add features to your models. For example, by declaring that one model `belongs_to` another, you instruct Rails to maintain Primary Key-Foreign Key information between instances of the two models, and you also get a number of utility methods added to your model. Rails supports six types of associations: * `belongs_to` * `has_one` @@ -261,7 +261,10 @@ With `through: :sections` specified, Rails will now understand: ### The `has_one :through` Association -A `has_one :through` association sets up a one-to-one connection with another model. This association indicates that the declaring model can be matched with one instance of another model by proceeding _through_ a third model. For example, if each supplier has one account, and each account is associated with one account history, then the customer model could look like this: +A `has_one :through` association sets up a one-to-one connection with another model. This association indicates +that the declaring model can be matched with one instance of another model by proceeding _through_ a third model. +For example, if each supplier has one account, and each account is associated with one account history, then the +supplier model could look like this: ```ruby class Supplier < ActiveRecord::Base @@ -337,7 +340,7 @@ class CreateAssembliesAndParts < ActiveRecord::Migration t.timestamps end - create_table :assemblies_parts do |t| + create_table :assemblies_parts, id: false do |t| t.belongs_to :assembly t.belongs_to :part end @@ -487,6 +490,19 @@ end With this setup, you can retrieve `@employee.subordinates` and `@employee.manager`. +In your migrations/schema, you will add a references column to the model itself. + +```ruby +class CreateEmployees < ActiveRecord::Migration + def change + create_table :employees do |t| + t.references :manager + t.timestamps + end + end +end +``` + Tips, Tricks, and Warnings -------------------------- @@ -555,7 +571,7 @@ If you create an association some time after you build the underlying model, you If you create a `has_and_belongs_to_many` association, you need to explicitly create the joining table. Unless the name of the join table is explicitly specified by using the `:join_table` option, Active Record creates the name by using the lexical order of the class names. So a join between customer and order models will give the default join table name of "customers_orders" because "c" outranks "o" in lexical ordering. -WARNING: The precedence between model names is calculated using the `<` operator for `String`. This means that if the strings are of different lengths, and the strings are equal when compared up to the shortest length, then the longer string is considered of higher lexical precedence than the shorter one. For example, one would expect the tables "paper\_boxes" and "papers" to generate a join table name of "papers\_paper\_boxes" because of the length of the name "paper\_boxes", but it in fact generates a join table name of "paper\_boxes\_papers" (because the underscore '\_' is lexicographically _less_ than 's' in common encodings). +WARNING: The precedence between model names is calculated using the `<` operator for `String`. This means that if the strings are of different lengths, and the strings are equal when compared up to the shortest length, then the longer string is considered of higher lexical precedence than the shorter one. For example, one would expect the tables "paper_boxes" and "papers" to generate a join table name of "papers_paper_boxes" because of the length of the name "paper_boxes", but it in fact generates a join table name of "paper_boxes_papers" (because the underscore '_' is lexicographically _less_ than 's' in common encodings). Whatever the name, you must manually generate the join table with an appropriate migration. For example, consider these associations: @@ -715,12 +731,13 @@ The `belongs_to` association creates a one-to-one match with another model. In d #### Methods Added by `belongs_to` -When you declare a `belongs_to` association, the declaring class automatically gains four methods related to the association: +When you declare a `belongs_to` association, the declaring class automatically gains five methods related to the association: * `association(force_reload = false)` * `association=(associate)` * `build_association(attributes = {})` * `create_association(attributes = {})` +* `create_association!(attributes = {})` In all of these methods, `association` is replaced with the symbol passed as the first argument to `belongs_to`. For example, given the declaration: @@ -737,6 +754,7 @@ customer customer= build_customer create_customer +create_customer! ``` NOTE: When initializing a new `has_one` or `belongs_to` association you must use the `build_` prefix to build the association, rather than the `association.build` method that would be used for `has_many` or `has_and_belongs_to_many` associations. To create one, use the `create_` prefix. @@ -777,6 +795,10 @@ The `create_association` method returns a new object of the associated type. Thi customer_name: "John Doe") ``` +##### `create_association!(attributes = {})` + +Does the same as `create_association` above, but raises `ActiveRecord::RecordInvalid` if the record is invalid. + #### Options for `belongs_to` @@ -855,8 +877,12 @@ end Counter cache columns are added to the containing model's list of read-only attributes through `attr_readonly`. ##### `:dependent` +If you set the `:dependent` option to: -If you set the `:dependent` option to `:destroy`, then deleting this object will call the `destroy` method on the associated object to delete that object. If you set the `:dependent` option to `:delete`, then deleting this object will delete the associated object _without_ calling its `destroy` method. If you set the `:dependent` option to `:restrict`, then attempting to delete this object will result in a `ActiveRecord::DeleteRestrictionError` if there are any associated objects. +* `:destroy`, when the object is destroyed, `destroy` will be called on its +associated objects. +* `:delete`, when the object is destroyed, all its associated objects will be +deleted directly from the database without calling their `destroy` method. WARNING: You should not specify this option on a `belongs_to` association that is connected with a `has_many` association on the other class. Doing so can lead to orphaned records in your database. @@ -947,7 +973,7 @@ end ##### `includes` -You can use the `includes` method let you specify second-order associations that should be eager-loaded when this association is used. For example, consider these models: +You can use the `includes` method to specify second-order associations that should be eager-loaded when this association is used. For example, consider these models: ```ruby class LineItem < ActiveRecord::Base @@ -1013,12 +1039,13 @@ The `has_one` association creates a one-to-one match with another model. In data #### Methods Added by `has_one` -When you declare a `has_one` association, the declaring class automatically gains four methods related to the association: +When you declare a `has_one` association, the declaring class automatically gains five methods related to the association: * `association(force_reload = false)` * `association=(associate)` * `build_association(attributes = {})` * `create_association(attributes = {})` +* `create_association!(attributes = {})` In all of these methods, `association` is replaced with the symbol passed as the first argument to `has_one`. For example, given the declaration: @@ -1035,6 +1062,7 @@ account account= build_account create_account +create_account! ``` NOTE: When initializing a new `has_one` or `belongs_to` association you must use the `build_` prefix to build the association, rather than the `association.build` method that would be used for `has_many` or `has_and_belongs_to_many` associations. To create one, use the `create_` prefix. @@ -1073,6 +1101,10 @@ The `create_association` method returns a new object of the associated type. Thi @account = @supplier.create_account(terms: "Net 30") ``` +##### `create_association!(attributes = {})` + +Does the same as `create_association` above, but raises `ActiveRecord::RecordInvalid` if the record is invalid. + #### Options for `has_one` While Rails uses intelligent defaults that will work well in most situations, there may be times when you want to customize the behavior of the `has_one` association reference. Such customizations can easily be accomplished by passing options when you create the association. For example, this association uses two such options: @@ -1125,6 +1157,12 @@ Controls what happens to the associated object when its owner is destroyed: * `:restrict_with_exception` causes an exception to be raised if there is an associated record * `:restrict_with_error` causes an error to be added to the owner if there is an associated object +It's necessary not to set or leave `:nullify` option for those associations +that have `NOT NULL` database constraints. If you don't set `dependent` to +destroy such associations you won't be able to change the associated object +because initial associated object foreign key will be set to unallowed `NULL` +value. + ##### `:foreign_key` By convention, Rails assumes that the column used to hold the foreign key on the other model is the name of this model with the suffix `_id` added. The `:foreign_key` option lets you set the name of the foreign key directly: @@ -1268,7 +1306,7 @@ The `has_many` association creates a one-to-many relationship with another model #### Methods Added by `has_many` -When you declare a `has_many` association, the declaring class automatically gains 13 methods related to the association: +When you declare a `has_many` association, the declaring class automatically gains 16 methods related to the association: * `collection(force_reload = false)` * `collection<<(object, ...)` @@ -1285,6 +1323,7 @@ When you declare a `has_many` association, the declaring class automatically gai * `collection.exists?(...)` * `collection.build(attributes = {}, ...)` * `collection.create(attributes = {})` +* `collection.create!(attributes = {})` In all of these methods, `collection` is replaced with the symbol passed as the first argument to `has_many`, and `collection_singular` is replaced with the singularized version of that symbol. For example, given the declaration: @@ -1312,6 +1351,7 @@ orders.where(...) orders.exists?(...) orders.build(attributes = {}, ...) orders.create(attributes = {}) +orders.create!(attributes = {}) ``` ##### `collection(force_reload = false)` @@ -1427,6 +1467,10 @@ The `collection.create` method returns a new object of the associated type. This order_number: "A12345") ``` +##### `collection.create!(attributes = {})` + +Does the same as `collection.create` above, but raises `ActiveRecord::RecordInvalid` if the record is invalid. + #### Options for `has_many` While Rails uses intelligent defaults that will work well in most situations, there may be times when you want to customize the behavior of the `has_many` association reference. Such customizations can easily be accomplished by passing options when you create the association. For example, this association uses two such options: @@ -1511,6 +1555,20 @@ end By convention, Rails assumes that the column used to hold the primary key of the association is `id`. You can override this and explicitly specify the primary key with the `:primary_key` option. +Let's say that `users` table has `id` as the primary_key but it also has +`guid` column. And the requirement is that `todos` table should hold +`guid` column value and not `id` value. This can be achieved like this + +```ruby +class User < ActiveRecord::Base + has_many :todos, primary_key: :guid +end +``` + +Now if we execute `@user.todos.create` then `@todo` record will have +`user_id` value as the `guid` value of `@user`. + + ##### `:source` The `:source` option specifies the source association name for a `has_many :through` association. You only need to use this option if the name of the source association cannot be automatically inferred from the association name. @@ -1678,7 +1736,7 @@ person.posts.inspect # => [#<Post id: 5, name: "a1">, #<Post id: 5, name: "a1">] Reading.all.inspect # => [#<Reading id: 12, person_id: 5, post_id: 5>, #<Reading id: 13, person_id: 5, post_id: 5>] ``` -In the above case there are two readings and `person.posts` brings out both of +In the above case there are two readings and `person.posts` brings out both of them even though these records are pointing to the same post. Now let's set `distinct`: @@ -1697,24 +1755,24 @@ person.posts.inspect # => [#<Post id: 7, name: "a1">] Reading.all.inspect # => [#<Reading id: 16, person_id: 7, post_id: 7>, #<Reading id: 17, person_id: 7, post_id: 7>] ``` -In the above case there are still two readings. However `person.posts` shows +In the above case there are still two readings. However `person.posts` shows only one post because the collection loads only unique records. -If you want to make sure that, upon insertion, all of the records in the -persisted association are distinct (so that you can be sure that when you -inspect the association that you will never find duplicate records), you should -add a unique index on the table itself. For example, if you have a table named -``person_posts`` and you want to make sure all the posts are unique, you could +If you want to make sure that, upon insertion, all of the records in the +persisted association are distinct (so that you can be sure that when you +inspect the association that you will never find duplicate records), you should +add a unique index on the table itself. For example, if you have a table named +`person_posts` and you want to make sure all the posts are unique, you could add the following in a migration: ```ruby -add_index :person_posts, :post, :unique => true +add_index :person_posts, :post, unique: true ``` -Note that checking for uniqueness using something like ``include?`` is subject -to race conditions. Do not attempt to use ``include?`` to enforce distinctness -in an association. For instance, using the post example from above, the -following code would be racy because multiple users could be attempting this +Note that checking for uniqueness using something like `include?` is subject +to race conditions. Do not attempt to use `include?` to enforce distinctness +in an association. For instance, using the post example from above, the +following code would be racy because multiple users could be attempting this at the same time: ```ruby @@ -1737,7 +1795,7 @@ The `has_and_belongs_to_many` association creates a many-to-many relationship wi #### Methods Added by `has_and_belongs_to_many` -When you declare a `has_and_belongs_to_many` association, the declaring class automatically gains 13 methods related to the association: +When you declare a `has_and_belongs_to_many` association, the declaring class automatically gains 16 methods related to the association: * `collection(force_reload = false)` * `collection<<(object, ...)` @@ -1754,6 +1812,7 @@ When you declare a `has_and_belongs_to_many` association, the declaring class au * `collection.exists?(...)` * `collection.build(attributes = {})` * `collection.create(attributes = {})` +* `collection.create!(attributes = {})` In all of these methods, `collection` is replaced with the symbol passed as the first argument to `has_and_belongs_to_many`, and `collection_singular` is replaced with the singularized version of that symbol. For example, given the declaration: @@ -1781,6 +1840,7 @@ assemblies.where(...) assemblies.exists?(...) assemblies.build(attributes = {}, ...) assemblies.create(attributes = {}) +assemblies.create!(attributes = {}) ``` ##### Additional Column Methods @@ -1900,14 +1960,18 @@ The `collection.create` method returns a new object of the associated type. This @assembly = @part.assemblies.create({assembly_name: "Transmission housing"}) ``` +##### `collection.create!(attributes = {})` + +Does the same as `collection.create`, but raises `ActiveRecord::RecordInvalid` if the record is invalid. + #### Options for `has_and_belongs_to_many` While Rails uses intelligent defaults that will work well in most situations, there may be times when you want to customize the behavior of the `has_and_belongs_to_many` association reference. Such customizations can easily be accomplished by passing options when you create the association. For example, this association uses two such options: ```ruby class Parts < ActiveRecord::Base - has_and_belongs_to_many :assemblies, uniq: true, - read_only: true + has_and_belongs_to_many :assemblies, autosave: true, + readonly: true end ``` @@ -1919,6 +1983,7 @@ The `has_and_belongs_to_many` association supports these options: * `:foreign_key` * `:join_table` * `:validate` +* `:readonly` ##### `:association_foreign_key` @@ -1928,7 +1993,7 @@ TIP: The `:foreign_key` and `:association_foreign_key` options are useful when s ```ruby class User < ActiveRecord::Base - has_and_belongs_to_many :friends, + has_and_belongs_to_many :friends, class_name: "User", foreign_key: "this_user_id", association_foreign_key: "other_user_id" @@ -2133,7 +2198,7 @@ You're not limited to the functionality that Rails automatically builds into ass class Customer < ActiveRecord::Base has_many :orders do def find_by_order_prefix(order_number) - find_by_region_id(order_number[0..2]) + find_by(region_id: order_number[0..2]) end end end |