Question

在我的模型中，我做了这个自定义的SQL查询：

SELECT
    training_courses.id,
    training_courses.training_id,
    training_courses.course_id,
    training_courses.is_pre_test, 
    training_courses.order_by,
    training_course_histories.id AS training_course_history_id, 
    training_course_histories.finished_at,
    training_course_histories.score,
    CAST(coalesce(user_training_courses.id, 0) as BOOLEAN) as purchased
FROM
    training_courses
    LEFT OUTER JOIN training_course_histories
        ON training_course_histories.training_course_id = training_courses.id AND training_course_histories.id = (
            SELECT th1.id
            FROM training_course_histories th1      
            WHERE th1.training_course_id = training_courses.id
              AND th1.finished_at IS NOT NULL
              AND th1.user_id = 1
            ORDER BY th1.finished_at DESC LIMIT 1
        )
    LEFT OUTER JOIN user_training_courses
        ON user_training_courses.training_course_id = training_courses.id AND user_training_courses.id = (
            SELECT th2.id
            FROM user_training_courses th2          
            WHERE th2.training_course_id = training_courses.id 
              AND th2.user_id = 1
        )
WHERE (training_courses.training_id = 1)
GROUP BY
    training_courses.id,
    training_courses.id,
    training_courses.training_id,
    training_courses.course_id,
    training_courses.is_pre_test, 
    training_courses.order_by,
    training_course_histories.id,
    training_course_histories.finished_at,
    training_course_histories.score, 
    user_training_courses.id
ORDER BY 
    order_by ASC, 
    id ASC, 
    training_courses.order_by ASC, 
    training_courses.id ASC

以前，我使用的是Mysql数据库，所以没问题，查询就像：ISNULL(user_training_courses.id) as purchased

但现在，我正在使用Postgres，我必须拥有CAST(coalesce(user_training_courses.id, 0) as BOOLEAN) as purchased

问题：对于Rails，购买='t'或'f'（字符串）

我想要的：购买=真或假（布尔）

有可能吗？

THX。

Answer 1

最后，我宁愿在我的模型中使用一个访问器来处理这种情况。

def purchased
  ![false, 'false', 'f', 'FALSE', 'F', 0, '0'].include?(self[:purchased])
end

Answer 2

Rails PostgreSQL驱动程序理解PostgreSQL布尔值是't'和'f'，通常可以正确翻译它们。您的CAST：

CAST(coalesce(user_training_courses.id, 0) as BOOLEAN)

也应该没问题：

psql=> select cast(11 as boolean), cast(1 as boolean), cast(0 as boolean);
 bool | bool | bool 
------+------+------
 t    | t    | f

所以我猜Rails只是不知道你的CAST的列类型。例如：

rails > ActiveRecord::Base.connection.select_rows('select cast(1 as boolean), 11 = 11')
 => [["t", "t"]]

您可以使用't'中的设置常量将'f'和ActiveRecord::ConnectionAdapters::Column转换为布尔值：

TRUE_VALUES = [true, 1, '1', 't', 'T', 'true', 'TRUE'].to_set
FALSE_VALUES = [false, 0, '0', 'f', 'F', 'false', 'FALSE'].to_set

或者您可以使用ActiveRecord::ConnectionAdapters::Column.value_to_boolean：

rails > ActiveRecord::Base.connection.select_rows('select cast(1 as boolean), 11 = 11').map { |r| r.map { |b| ActiveRecord::ConnectionAdapters::Column.value_to_boolean(b) } }
 => [[true, true]]

但是如果您要使用低级SQL接口，您仍然需要知道所有列的类型并手动排序。类似的问题适用于整数，日期以及您获得的任何其他非字符串类型。

如何在Rails 3 + Postgres中使用自定义sql查询检索BOOLEANS？

2 个答案: