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Diffstat (limited to 'guides/source/active_record_querying.md')
| -rw-r--r-- | guides/source/active_record_querying.md | 97 |
1 files changed, 48 insertions, 49 deletions
diff --git a/guides/source/active_record_querying.md b/guides/source/active_record_querying.md index 4725e2c8a2..2a76df156c 100644 --- a/guides/source/active_record_querying.md +++ b/guides/source/active_record_querying.md @@ -707,7 +707,7 @@ You can additionally unscope specific where clauses. For example: ```ruby Post.where(id: 10, trashed: false).unscope(where: :id) -# => SELECT "posts".* FROM "posts" WHERE trashed = 0 +# SELECT "posts".* FROM "posts" WHERE trashed = 0 ``` A relation which has used `unscope` will affect any relation it is @@ -715,7 +715,7 @@ merged in to: ```ruby Post.order('id asc').merge(Post.unscope(:order)) -# => SELECT "posts".* FROM "posts" +# SELECT "posts".* FROM "posts" ``` ### `only` @@ -961,7 +961,7 @@ SELECT clients.* FROM clients LEFT OUTER JOIN addresses ON addresses.client_id = WARNING: This method only works with `INNER JOIN`. -Active Record lets you use the names of the [associations](association_basics.html) defined on the model as a shortcut for specifying `JOIN` clause for those associations when using the `joins` method. +Active Record lets you use the names of the [associations](association_basics.html) defined on the model as a shortcut for specifying `JOIN` clauses for those associations when using the `joins` method. For example, consider the following `Category`, `Post`, `Comment`, `Guest` and `Tag` models: @@ -1231,6 +1231,35 @@ Using a class method is the preferred way to accept arguments for scopes. These category.posts.created_before(time) ``` +### Applying a default scope + +If we wish for a scope to be applied across all queries to the model we can use the +`default_scope` method within the model itself. + +```ruby +class Client < ActiveRecord::Base + default_scope { where("removed_at IS NULL") } +end +``` + +When queries are executed on this model, the SQL query will now look something like +this: + +```sql +SELECT * FROM clients WHERE removed_at IS NULL +``` + +If you need to do more complex things with a default scope, you can alternatively +define it as a class method: + +```ruby +class Client < ActiveRecord::Base + def self.default_scope + # Should return an ActiveRecord::Relation. + end +end +``` + ### Merging of scopes Just like `where` clauses scopes are merged using `AND` conditions. @@ -1242,26 +1271,26 @@ class User < ActiveRecord::Base end User.active.inactive -# => SELECT "users".* FROM "users" WHERE "users"."state" = 'active' AND "users"."state" = 'inactive' +# SELECT "users".* FROM "users" WHERE "users"."state" = 'active' AND "users"."state" = 'inactive' ``` We can mix and match `scope` and `where` conditions and the final sql -will have all conditions joined with `AND` . +will have all conditions joined with `AND`. ```ruby User.active.where(state: 'finished') -# => SELECT "users".* FROM "users" WHERE "users"."state" = 'active' AND "users"."state" = 'finished' +# SELECT "users".* FROM "users" WHERE "users"."state" = 'active' AND "users"."state" = 'finished' ``` If we do want the `last where clause` to win then `Relation#merge` can -be used . +be used. ```ruby User.active.merge(User.inactive) -# => SELECT "users".* FROM "users" WHERE "users"."state" = 'inactive' +# SELECT "users".* FROM "users" WHERE "users"."state" = 'inactive' ``` -One important caveat is that `default_scope` will be overridden by +One important caveat is that `default_scope` will be prepended in `scope` and `where` conditions. ```ruby @@ -1272,48 +1301,18 @@ class User < ActiveRecord::Base end User.all -# => SELECT "users".* FROM "users" WHERE "users"."state" = 'pending' +# SELECT "users".* FROM "users" WHERE "users"."state" = 'pending' User.active -# => SELECT "users".* FROM "users" WHERE "users"."state" = 'active' +# SELECT "users".* FROM "users" WHERE "users"."state" = 'pending' AND "users"."state" = 'active' User.where(state: 'inactive') -# => SELECT "users".* FROM "users" WHERE "users"."state" = 'inactive' +# SELECT "users".* FROM "users" WHERE "users"."state" = 'pending' AND "users"."state" = 'inactive' ``` -As you can see above the `default_scope` is being overridden by both +As you can see above the `default_scope` is being merged in both `scope` and `where` conditions. - -### Applying a default scope - -If we wish for a scope to be applied across all queries to the model we can use the -`default_scope` method within the model itself. - -```ruby -class Client < ActiveRecord::Base - default_scope { where("removed_at IS NULL") } -end -``` - -When queries are executed on this model, the SQL query will now look something like -this: - -```sql -SELECT * FROM clients WHERE removed_at IS NULL -``` - -If you need to do more complex things with a default scope, you can alternatively -define it as a class method: - -```ruby -class Client < ActiveRecord::Base - def self.default_scope - # Should return an ActiveRecord::Relation. - end -end -``` - ### Removing All Scoping If we wish to remove scoping for any reason we can use the `unscoped` method. This is @@ -1338,11 +1337,6 @@ Client.unscoped { Dynamic Finders --------------- -NOTE: Dynamic finders have been deprecated in Rails 4.0 and will be -removed in Rails 4.1. The best practice is to use Active Record scopes -instead. You can find the deprecation gem at -https://github.com/rails/activerecord-deprecated_finders - For every field (also known as an attribute) you define in your table, Active Record provides a finder method. If you have a field called `first_name` on your `Client` model for example, you get `find_by_first_name` for free from Active Record. If you have a `locked` field on the `Client` model, you also get `find_by_locked` and methods. You can specify 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 `Client.find_by_name!("Ryan")` @@ -1352,6 +1346,11 @@ If you want to find both by name and locked, you can chain these finders togethe Find or Build a New Object -------------------------- +NOTE: Some dynamic finders have been deprecated in Rails 4.0 and will be +removed in Rails 4.1. The best practice is to use Active Record scopes +instead. You can find the deprecation gem at +https://github.com/rails/activerecord-deprecated_finders + It's common that you need to find a record or create it if it doesn't exist. You can do that with the `find_or_create_by` and `find_or_create_by!` methods. ### `find_or_create_by` @@ -1455,7 +1454,7 @@ If you'd like to use your own SQL to find records in a table you can use `find_b ```ruby Client.find_by_sql("SELECT * FROM clients INNER JOIN orders ON clients.id = orders.client_id - ORDER clients.created_at desc") + ORDER BY clients.created_at desc") ``` `find_by_sql` provides you with a simple way of making custom calls to the database and retrieving instantiated objects. |