Question

我具有以下数据库结构：

String sql = " "
        + "SET NOCOUNT ON; "
        + "DECLARE @cols AS NVARCHAR(MAX), @query  AS NVARCHAR(MAX); "
        + " "
        + "SET @cols =  "
        + "    STUFF( "
        + "        ( "
        + "            SELECT distinct ',' + QUOTENAME([case owner])  "
        + "            FROM StatusTable c "
        + "            FOR XML PATH(''), TYPE "
        + "        ).value('.', 'NVARCHAR(MAX)'), "
        + "        1, "
        + "        1, "
        + "        ''); "
        + " "
        + "set @query = 'select * "
        + "from "
        + "( "
        + "    select [case owner], [time taken(minutes)] from StatusTable "
        + ") as pivotdata "
        + "pivot( "
        + "    sum([time taken(minutes)]) for [CASE OWNER] in ('+@cols+') "
        + ") as pivoting'; "
        +" "
        + "execute(@query); ";
Statement st = conn.createStatement();
ResultSet rs = st.executeQuery(sql);
ResultSetMetaData rsmd = rs.getMetaData();
// print column headings
for (int i = 1; i <= rsmd.getColumnCount(); i++) {
    System.out.printf("%5s", rsmd.getColumnLabel(i));
}
System.out.println();
rs.next();
// print column values
for (int i = 1; i <= rsmd.getColumnCount(); i++) {
    System.out.printf("%5s", rs.getString(i));
}
System.out.println();
/* console output:

   AAA  BBB  XXX
     2   13    1

 */

现在，我要查找所有没有将特定属性设置为true的孩子的父母。

示例：

Parent
 -> child 1
 -> child 2
 ->..

目前，我有以下内容：

Should not be found: 
Parent: 
 -> child 1 (selected: true)
 -> child 2 (selected: false)

Should be found
Parent: 
 -> child 1 (selected: nil)
 -> child 2 (selected: false)

这很好用，但似乎效率低下。我相信应该有一个更简便，更快捷的方法。

Answer 1

    parents = Parent.joins(:children).where('children.selected = FALSE or children.selected is NULL')

此查询从父子内部联接表中选择行，且所选属性未设置为true。

如果想要父对象甚至没有关联的子代，则必须保留外部联接子代。

Parent.joins('left join children on parents.id = childrenparent_id')..where('children.selected = FALSE or children.selected is NULL')

Answer 2

您只能使用where.not解决它。

请参阅 https://api.rubyonrails.org/classes/ActiveRecord/QueryMethods/WhereChain.html#method-i-not

Project.joins(:project_images).where.not(project_images: { selected: true })

Answer 3

Project.joins（：project_images）.where（“ project_images.selected NOT IN（TRUE）”）;

活动记录：如何基于与指定属性没有关联的父项来查找父项

3 个答案: