CODEWITHSUNDEEP
javascriptdatabasemongodbmongoose
billy.Lin
billy.Lin

Reputation: 13

how to sorting according to the value of a field? mongo

I have a set of data. When I select the filter conditions, I want to query all the data and put the values that conform to the screening conditions to display in front of the query results.

for example

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

when i choose color:red, and limit 4, I want to get the data

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

and when i choose color:blue, and limit 4, I want to get the data

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

Have some function to achieve this？

My english is so poor, I hope the meaning is clear.

anyway, thanks!

Upvotes: 0

Views: 377

Answers (2)

dnickless
dnickless

Reputation: 10918

In your specific example you can write this:

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
}])

If you are using an older version of MongoDB (<3.4) that does not support $addFields yet you can instead resort to using $project instead like so:

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
}])

Upvotes: 0

Neodan
Neodan

Reputation: 5252

If you are using the find function, then you can use the sort function. If the aggregation framework, then the pipeline $sort stage.

Upvotes: 1

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