diff options
Diffstat (limited to 'guides/source/active_record_querying.textile')
| -rw-r--r-- | guides/source/active_record_querying.textile | 31 |
1 files changed, 11 insertions, 20 deletions
diff --git a/guides/source/active_record_querying.textile b/guides/source/active_record_querying.textile index de55401c1f..f9dbaa1125 100644 --- a/guides/source/active_record_querying.textile +++ b/guides/source/active_record_querying.textile @@ -356,20 +356,6 @@ Client.where("created_at >= :start_date AND created_at <= :end_date", This makes for clearer readability if you have a large number of variable conditions. -h5(#array-range_conditions). Range Conditions - -If you're looking for a range inside of a table (for example, users created in a certain timeframe) you can use the conditions option coupled with the +IN+ SQL statement for this. If you had two dates coming in from a controller you could do something like this to look for a range: - -<ruby> -Client.where(:created_at => (params[:start_date].to_date)..(params[:end_date].to_date)) -</ruby> - -This query will generate something similar to the following SQL: - -<sql> - SELECT "clients".* FROM "clients" WHERE ("clients"."created_at" BETWEEN '2010-09-29' AND '2010-11-30') -</sql> - h4. Hash Conditions Active Record also allows you to pass in hash conditions which can increase the readability of your conditions syntax. With hash conditions, you pass in a hash with keys of the fields you want conditionalised and the values of how you want to conditionalise them: @@ -388,9 +374,9 @@ The field name can also be a string: Client.where('locked' => true) </ruby> -h5(#hash-range_conditions). Range Conditions +NOTE: The values cannot be symbols. For example, you cannot do +Client.where(:status => :active)+. -The good thing about this is that we can pass in a range for our fields without it generating a large query as shown in the preamble of this section. +h5(#hash-range_conditions). Range Conditions <ruby> Client.where(:created_at => (Time.now.midnight - 1.day)..Time.now.midnight) @@ -539,7 +525,9 @@ And this will give you a single +Order+ object for each date where there are ord The SQL that would be executed would be something like this: <sql> -SELECT date(created_at) as ordered_date, sum(price) as total_price FROM orders GROUP BY date(created_at) +SELECT date(created_at) as ordered_date, sum(price) as total_price +FROM orders +GROUP BY date(created_at) </sql> h3. Having @@ -555,7 +543,10 @@ Order.select("date(created_at) as ordered_date, sum(price) as total_price").grou The SQL that would be executed would be something like this: <sql> -SELECT date(created_at) as ordered_date, sum(price) as total_price FROM orders GROUP BY date(created_at) HAVING sum(price) > 100 +SELECT date(created_at) as ordered_date, sum(price) as total_price +FROM orders +GROUP BY date(created_at) +HAVING sum(price) > 100 </sql> This will return single order objects for each day, but only those that are ordered more than $100 in a day. @@ -829,7 +820,7 @@ SELECT categories.* FROM categories INNER JOIN posts ON posts.category_id = categories.id </sql> -Or, in English: "return a Category object for all categories with posts". Note that you will see duplicate categories if more than one post has the same category. If you want unique categories, you can use Category.joins(:post).select("distinct(categories.id)"). +Or, in English: "return a Category object for all categories with posts". Note that you will see duplicate categories if more than one post has the same category. If you want unique categories, you can use Category.joins(:posts).select("distinct(categories.id)"). h5. Joining Multiple Associations @@ -919,7 +910,7 @@ This code looks fine at the first sight. But the problem lies within the total n Active Record lets you specify in advance all the associations that are going to be loaded. This is possible by specifying the +includes+ method of the +Model.find+ call. With +includes+, Active Record ensures that all of the specified associations are loaded using the minimum possible number of queries. -Revisiting the above case, we could rewrite +Client.all+ to use eager load addresses: +Revisiting the above case, we could rewrite +Client.limit(10)+ to use eager load addresses: <ruby> clients = Client.includes(:address).limit(10) |