如何动态构建mongodb查询 [英] How to dynamically build mongodb query

问题描述

我在mongodb聚合中有一个match表达式.比赛中包含3个字段，但它们并不总是包含数据.如果字段不为空，我只想在比赛中包括这些字段.

I have a match expression in a mongodb aggregation. There are 3 fields that are included in the match but they don't all always contain data. I only want to include the fields in the match if the field isn't empty.

如果所有字段都有数据，但是例如，如果用于studentGradeLevels的数组为空，则匹配看起来是这样，那么我不想包含它，或者我希望查询仍然返回数据而忽略空参数.

This is what the match looks like if all fields have data but for example, if the array used for studentGradeLevels is empty, then I don't want to include it or I want the query to still return data ignoring the empty parameter.

$match: {
    "school._id": "7011",
    "studentGradeLevels": { $in: ["09", "10", "11", "12"] },
    "contentArea": {
        $in: [
            "English 1"
        ]
    }
}

有没有一种方法可以动态构建匹配项，以便仅包含我要基于的字段是否为空，或者在查询中执行某些操作以忽略空的参数.

Is there a way to either dynamically build the match so that I only include the fields I want based on if they are empty or not or do something in the query so that parameters that are empty are ignored.

推荐答案

您可以使用 $nin 当数组为空时，这样将不考虑匹配字段($nin : []):

function buildMatch(arr) {
    var matcher = {};
    if (arr.length == 0)
        matcher["$nin"] = arr;
    else
        matcher["$in"] = arr;
    return matcher;
}

var grades = ["09", "10", "11", "12"];
var areas = [ "English 2" ];

var gradeMatch = buildMatch(grades);
var areaMatch = buildMatch(areas);

db.students.aggregate([{
    $match: {
        "school._id": "7011",
        "studentGradeLevels": gradeMatch,
        "contentArea": areaMatch
    }
}])

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