刚接触 mongo，还不知道如何执行查询。

我有一个 accounts 集合，如下所示:

{
    "_id" : ObjectId("1"),
    "time" : ISODate("2018-10-20T05:57:15.372Z"),
    "profileId" : "1",
    "totalUSD" : "1015.5513030613",
    "accounts" : [
        {
            "_id" : ObjectId("2"),
            "accountId" : "1",
            "currency" : "USD",
            "balance" : "530.7934159683763000",
            "available" : "530.7934159683763",
            "hold" : "0.0000000000000000",
            "exchangeRateUSD" : "1"
        },
        {
            "_id" : ObjectId("5"),
            "accountId" : "4",
            "currency" : "BTC",
            "balance" : "0.0759214200000000",
            "available" : "0.07592142",
            "hold" : "0.0000000000000000",
            "exchangeRateUSD" : "6384.995"
        },
    ],
}

我只存储每种货币的 exchangeRateUSD，而不存储 exchangeRateXXX，其中 XXX 是货币名称，因为可以有任意数量的货币和货币对。但是当我查询账户集合时，它总是会被货币对查询，例如:BTC-USD。现在保持简单，我可以假设货币对始终是 XXX-USD。

当我查询帐户集合时，我想为每个帐户对象添加一个“虚拟”字段:exchangeRateCrypto 然后在顶级帐户文档上我想添加 totalCrypto 这只是给定加密中的总账户值(value)。例如:美元账户余额 * exchangeRateCrypto + 加密账户余额 * exchangeRateCrypto(等于 1)。

没有 exchangeRateCrypto 和 totalCrypto 的当前查询如下所示:

db.accounts.aggregate([
  { $unwind: '$accounts' },
  { $match: { 'accounts.currency': { $in: [ 'USD', 'BTC' ] }}},
  {
    $group: {
      _id: '$_id',
      time: { $first: '$time' },
      profileId: { $first: '$profileId' },
      accounts:  { $push: '$accounts' },
      totalUSD: { $sum: { $multiply: [ { $toDouble: '$accounts.balance' }, { $toDouble: '$accounts.exchangeRateUSD' } ] } }
    }
  }
]);

我试图弄清楚如何通过简单地执行 1/exchangeRateUSD 然后投影/返回帐户来“到达”BTC 行并计算 exchangeRateCrypto文档和子文档为:

{
    "_id" : ObjectId("1"),
    "time" : ISODate("2018-10-20T05:57:15.372Z"),
    "profileId" : "1",
    "totalUSD" : "1015.5513030613",
    "totalCrypto" : "0.1590527953",   // 530.7934159683763 * 0.0001566171939 + 0.07592142 * 1
    "accounts" : [
        {
            "_id" : ObjectId("2"),
            "accountId" : "1",
            "currency" : "USD",
            "balance" : "530.7934159683763000",
            "available" : "530.7934159683763",
            "hold" : "0.0000000000000000",
            "exchangeRateUSD" : "1",
            "exchangeRateCrypto" : "0.0001566171939",   //  1 / 6384.995
        },
        {
            "_id" : ObjectId("5"),
            "accountId" : "4",
            "currency" : "BTC",
            "balance" : "0.0759214200000000",
            "available" : "0.07592142",
            "hold" : "0.0000000000000000",
            "exchangeRateUSD" : "6384.995",
            "exchangeRateCrypto" : "1"
        },
    ],
}

但还没有找到一个好的方法。

看起来应该很简单，但是还是在学习Mongo。

有什么建议吗？

谢谢!

最佳答案

解决方案可能有点长，可能会缩短，但我希望您逐步理解建议的思维方式。

var secondCurrency = "BTC";
var secondCurrencyFieldName = "exchangeRate" + secondCurrency;
var secondCurrencyFieldNameRef = "$" + secondCurrencyFieldName;
var totalFieldName = "total" + secondCurrency;

db.accounts.aggregate([
    { $unwind: "$accounts" },
    { $match: { "accounts.currency": { $in: [ "USD", secondCurrency ] }}},
    {
        $group: {
            _id: "$_id",
            time: { $first: "$time" },
            profileId: { $first: "$profileId" },
            accounts:  { $push: "$accounts" },
            totalUSD: { $sum: { $multiply: [ { $toDouble: "$accounts.balance" }, { $toDouble: "$accounts.exchangeRateUSD" } ] } }
        }
},
{
    $addFields: {
        [secondCurrencyFieldName]: {
            $filter: {
                input: "$accounts",
                as: "account",
                cond: { $eq: [  "$$account.currency", secondCurrency ] }
            }
        }
    }
},
{
    $addFields: {
        [secondCurrencyFieldName]: {
            $let: {
                vars: { first: { $arrayElemAt: [ secondCurrencyFieldNameRef, 0 ] } },
                in: { $toDouble: "$$first.exchangeRateUSD" }
            }
        }
    }
},
{
    $addFields: {
        accounts: {
            $map: {
                input: "$accounts",
                as: "account",
                in: {
                    $mergeObjects: [
                        "$$account",
                            { 
                            [secondCurrencyFieldName]: {
                                $cond: [ { $eq: [ "$$account.currency", secondCurrency ] }, 1, { $divide: [ 1, secondCurrencyFieldNameRef ] } ]
                                } 
                            }
                    ]
                }
            }
        }
    }
},
{
    $addFields: {
        [totalFieldName]: {
            $reduce: {
                input: "$accounts",
                initialValue: 0,
                in: {
                    $add: [
                        "$$value",
                        { $multiply: [ { $toDouble: "$$this.balance" }, "$$this." + secondCurrencyFieldName ] }
                    ]
                }
            }
        }
    }
}
]).pretty()

所以我们可以从$addFields开始它可以向现有文档添加新字段或替换现有字段。在 $group 阶段之后，您必须找到 USD-XXX 汇率(在下一个管道阶段使用 $filter 和 $let + $arrayElemAt)。有了这个值，您可以再次结合使用 $addFields 和 $map和 $mergeObjects向嵌套数组添加新字段，该字段将表示 USD 和 XXX 货币之间的比率。然后你可以再次使用 $addFields $reduce获取 XXX 货币的所有账户总数。

输出:

{
    "_id" : ObjectId("5beeec9fef99bb86541abf7f"),
    "time" : ISODate("2018-10-20T05:57:15.372Z"),
    "profileId" : "1",
    "accounts" : [
            {
                    "_id" : ObjectId("5beeec9fef99bb86541abf7d"),
                    "accountId" : "1",
                    "currency" : "USD",
                    "balance" : "530.7934159683763000",
                    "available" : "530.7934159683763",
                    "hold" : "0.0000000000000000",
                    "exchangeRateUSD" : "1",
                    "exchangeRateBTC" : 0.00015661719390539853
            },
            {
                    "_id" : ObjectId("5beeec9fef99bb86541abf7e"),
                    "accountId" : "4",
                    "currency" : "BTC",
                    "balance" : "0.0759214200000000",
                    "available" : "0.07592142",
                    "hold" : "0.0000000000000000",
                    "exchangeRateUSD" : "6384.995",
                    "exchangeRateBTC" : 1
            }
    ],
    "totalUSD" : 1015.5513030612763,
    "exchangeRateBTC" : 6384.995,
    "totalexchangeRateBTC" : 0.15905279535242806
}

关于mongodb - 是否可以将展开的数组的一个字段连接到展开的数组上？，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/53330969/