Question

我有一组数据。当我选择过滤条件时，我想查询所有数据并将符合筛选条件的值显示在查询结果的前面。

例如

[
    {color: 'blue', name: 'four'},
    {color: 'green', name: 'five'},
    {color: 'red', name: 'one'},
    {color: 'red', name: 'two'},
    {color: 'red', name: 'three'}
]

当我选择color:red并限制4时，我想获取数据

[
    {color: 'red', name: 'one'},
    {color: 'red', name: 'two'},
    {color: 'red', name: 'three'},
    {color .........}// the fourth of data are not concerned for now
]

当我选择color:blue并限制4时，我想获取数据

[
    {color: 'blue', name: 'four'},
    {color  ........},
    {color  ........},
    {color .........}// now just care the first data
]

有一些功能来实现这个目标吗？

我的英语太差了，我希望意思很清楚。

无论如何，谢谢！

Answer 1

如果您使用find功能，则可以使用sort功能。如果是聚合框架，那么管道$sort阶段。

Answer 2

在您的具体示例中，您可以写下：

db.color.aggregate([{
    $addFields : {
        "rank" : { // add a field called rank to all our documents
            $cond: {
                if: { $eq: [ "$color", "blue" ] }, // if the color value matches "blue"
                then: 0, // then we want items to be on the top
                else: 1 // else we want them to be in the second part
            }
        }
    }
}, {
    $sort : {"rank" : 1} // sort ascending by our newly created "rank" field
}])

如果您使用的旧版MongoDB（<3.4）不支持$addFields，您可以改为使用$project，而不是这样：

db.color.aggregate([{
    $project : {
        "color": 1, // we want to retain the value of the color field
        "name": 1, // the same goes for the name field
        "rank" : { // add a field called rank to all our documents
            $cond: {
                if: { $eq: [ "$color", "blue" ] }, // if the color value matches "blue"
                then: 0, // then we want items to be on the top
                else: 1 // else we want them to be in the second part
            }
        }
    }
}, {
    $sort : {"rank" : 1} // sort ascending by our newly created "rank" field
}])

如何根据字段的值进行排序？蒙戈

2 个答案: