Mongo DB聚合将数组转换为字符串

Question

有一个包含数据的集合

date_new:Array

使用mongodb聚合如何将其转换为这样的字符串，如果有空字符串，则将其转换为" "

date_new:Array
    0: " "

Answer 1

请尝试：

db.yourCollectionName.aggregate([{
    $addFields:
    {
        date_new: {
            $arrayToObject:
            {
                $map:
                {
                    input: "$date_new",
                    as: "each",
                    in: [{ $toString: { $indexOfArray: ["$date_new", '$$each'] } }, '$$each']
                }
            }
        }
    }
}])

收集数据：

/* 1 */
{
    "_id" : ObjectId("5e1e2a74d3c98f2a7100fd44"),
    "date_new" : [ 
        "abc", 
        "def", 
        ""
    ]
}

/* 2 */
{
    "_id" : ObjectId("5e1e2f25d3c98f2a7100fd45"),
    "date_new" : []
}

结果：

/* 1 */
{
    "_id" : ObjectId("5e1e2a74d3c98f2a7100fd44"),
    "date_new" : {
        "0" : "abc",
        "1" : "def",
        "2" : ""
    }
}

/* 2 */
{
    "_id" : ObjectId("5e1e2f25d3c98f2a7100fd45"),
    "date_new" : {}
}