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Diffstat (limited to 'railties/guides/source/active_record_querying.textile')
| -rw-r--r-- | railties/guides/source/active_record_querying.textile | 75 |
1 files changed, 68 insertions, 7 deletions
diff --git a/railties/guides/source/active_record_querying.textile b/railties/guides/source/active_record_querying.textile index 95a7bfebc3..7a853db813 100644 --- a/railties/guides/source/active_record_querying.textile +++ b/railties/guides/source/active_record_querying.textile @@ -1018,23 +1018,84 @@ If you want to find both by name and locked, you can chain these finders togethe WARNING: Up to and including Rails 3.1, when the number of arguments passed to a dynamic finder method is lesser than the number of fields, say <tt>Client.find_by_name_and_locked("Ryan")</tt>, the behavior is to pass +nil+ as the missing argument. This is *unintentional* and this behavior will be changed in Rails 3.2 to throw an +ArgumentError+. -There's another set of dynamic finders that let you find or create/initialize objects if they aren't found. These work in a similar fashion to the other finders and can be used like +find_or_create_by_first_name(params[:first_name])+. Using this will first perform a find and then create if the find returns +nil+. The SQL looks like this for +Client.find_or_create_by_first_name("Ryan")+: +h3. Find or build a new object + +It's common that you need to find a record or create it if it doesn't exist. You can do that with the +first_or_create+ and +first_or_create!+ methods. + +h4. +first_or_create+ + +The +first_or_create+ method checks whether +first+ returns +nil+ or not. If it does return +nil+, then +create+ is called. This is very powerful when coupled with the +where+ method. Let's see an example. + +Suppose you want to find a client named 'Andy', and if there's none, create one and additionally set his +locked+ attribute to false. You can do so by running: + +<ruby> +Client.where(:first_name => 'Andy').first_or_create(:locked => false) +# => <Client id: 1, first_name: "Andy", orders_count: 0, locked: false, created_at: "2011-08-30 06:09:27", updated_at: "2011-08-30 06:09:27"> +</ruby> + +The SQL generated by this method looks like this: <sql> -SELECT * FROM clients WHERE (clients.first_name = 'Ryan') LIMIT 1 +SELECT * FROM clients WHERE (clients.first_name = 'Andy') LIMIT 1 BEGIN -INSERT INTO clients (first_name, updated_at, created_at, orders_count, locked) - VALUES('Ryan', '2008-09-28 15:39:12', '2008-09-28 15:39:12', 0, '0') +INSERT INTO clients (created_at, first_name, locked, orders_count, updated_at) VALUES ('2011-08-30 05:22:57', 'Andy', 0, NULL, '2011-08-30 05:22:57') COMMIT </sql> -+find_or_create+'s sibling, +find_or_initialize+, will find an object and if it does not exist will act similarly to calling +new+ with the arguments you passed in. For example: ++first_or_create+ returns either the record that already existed or the new record. In our case, we didn't already have a client named Andy so the record was created an returned. + +The new record might not be saved to the database; that depends on whether validations passed or not (just like +create+). + +It's also worth noting that +first_or_create+ takes into account the arguments of the +where+ method. In the example above we didn't explicitly pass a +:first_name => 'Andy'+ argument to +first_or_create+. However, that was used when creating the new record because it was already passed before to the +where+ method. + +NOTE: On previous versions of Rails you could do a similar thing with the +find_or_create_by+ method. Following our example, you could also run something like +Client.find_or_create_by_first_name(:first_name => "Andy", :locked => false)+. This method still works, but it's encouraged to use +first_or_create+ because it's more explicit on what arguments are used to _find_ the record and what arguments are used to _create_ it, resulting in less confusion overall. + +h4. +first_or_create!+ + +You can also use +first_or_create!+ to raise an exception if the new record is invalid. Validations are not covered on this guide, but let's assume for a moment that you temporarily add + +<ruby> + validates :orders_count, :presence => true +</ruby> + +to your +Client+ model. If you try to create a new +Client+ without passing an +orders_count+, the record will be invalid and an exception will be raised: + +<ruby> +Client.where(:first_name => 'Andy').first_or_create!(:locked => false) +# => ActiveRecord::RecordInvalid: Validation failed: Orders count can't be blank +</ruby> + +NOTE: Be sure to check the extensive *Active Record Validations and Callbacks Guide* for more information about validations. + +h4. +first_or_new+ + +The +first_or_new+ method will work just like +first_or_create+ but it will not call +create+ but +new+. This means that a new model instance will be created in memory but won't be saved to the database. Continuing with the +first_or_create+ example, we now want the client named 'Nick': + +<ruby> +nick = Client.where(:first_name => 'Nick').first_or_new(:locked => false) +# => <Client id: nil, first_name: "Nick", orders_count: 0, locked: false, created_at: "2011-08-30 06:09:27", updated_at: "2011-08-30 06:09:27"> + +nick.persisted? +# => false + +nick.new_record? +# => true +</ruby> + +Because the object is not yet stored in the database, the SQL generated looks like this: + +<sql> +SELECT * FROM clients WHERE (clients.first_name = 'Nick') LIMIT 1 +</sql> + +When you want to save it to the database, just call +save+: <ruby> -client = Client.find_or_initialize_by_first_name('Ryan') +nick.save +# => true </ruby> -will either assign an existing client object with the name "Ryan" to the client local variable, or initialize a new object similar to calling +Client.new(:first_name => 'Ryan')+. From here, you can modify other fields in client by calling the attribute setters on it: +client.locked = true+ and when you want to write it to the database just call +save+ on it. +Just like you can use *+build+* instead of *+new+*, you can use *+first_or_build+* instead of *+first_or_new+*. h3. Finding by SQL |