MongoDB：如何对仅在$project中出现的字段进行乘法操作？

huangapple
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英文:

MongoDB : How to multiply a field that appears only in $project?

问题

我正在使用以下方式连接两个集合（$lookup）：

  1. const LEAD_PRICE = ....; // 不重要
  2. Client.aggregate(
  3.     [
  4.         {
  5.             $lookup: {
  6.                 from: "clientboughtleads",
  7.                 localField: "_id",
  8.                 foreignField: "Client",
  9.                 as: "ClientLeads"
  10.             }
  11.         },
  13.         {
  14.             $project: {
  15.                 ClientId: "$_id",
  16.                 RegistrationDate: "$date",
  17.                 TotalPurchasedLeads: {
  18.                     $size: "$ClientLeads"
  19.                 },
  20.                 IncomeFromClient: { // 这个总是未定义
  21.                     $multiply: [LEAD_PRICE / 2, "$TotalPurchasedLeads"]
  22.                 }
  23.             }
  24.         }
  25.     ]
  26. )

我想通过常量和一个已计算的字段TotalPurchasedLeads的乘积来计算IncomeFromClient，但它返回了NULL：

  1. [
  2.     {
  3.         _id: 5e0e43ae82a71e0017dccb20,
  4.         ClientId: 5e0e43ae82a71e0017dccb20,
  5.         RegistrationDate: 2020-01-02T21:25:34.000Z,
  6.         TotalPurchasedLeads: 4,
  7.         IncomeFromClient: null // 这个未计算
  8.     }
  9. ]

在计算一个被$project的字段时，如何获取$lookup集合的大小？

英文:

I'm joining ($lookup) two collection the following way :

  1.   const LEAD_PRICE  = ....; // doesn't matter 
  2.   Client.aggregate(
  3.       [
  4.         {
  5.           $lookup: {
  6.             from: "clientboughtleads",
  7.             localField: "_id",
  8.             foreignField: "Client",
  9.             as: "ClientLeads"
  10.           }
  11.         },
  13.         {
  14.           $project: {
  15.             ClientId: "$_id",
  16.             RegistrationDate: "$date",
  17.             TotalPurchasedLeads: {
  18.               $size: "$ClientLeads"
  19.             },
  20.             IncomeFromClient: {     // This one is always undefined
  21.               $multiply: [LEAD_PRICE / 2, "$TotalPurchasedLeads"]
  22.             }
  23.           }
  24.         }
  25.       ]

I want to calculate IncomeFromClient by the mul of a const and a field that is been also calculated - TotalPurchasedLeads , however it returns NULL :

  1.  [
  2. [0]   {
  3. [0]     _id: 5e0e43ae82a71e0017dccb20,
  4. [0]     ClientId: 5e0e43ae82a71e0017dccb20,
  5. [0]     RegistrationDate: 2020-01-02T21:25:34.000Z,
  6. [0]     TotalPurchasedLeads: 4,
  7. [0]     IncomeFromClient: null      // This one is not calculated 
  8. [0]   }
  9. [0] ]

How can I get the size of the $lookup collection when calculating a field that is being $projected ?

答案1

得分: 1

请在我们可以在项目中使用关键字"addFields"之后使用"key"。

  1. const LEAD_PRICE = ....; // doesn't matter 
  2. Client.aggregate(
  3.     [
  4.         {
  5.             $lookup: {
  6.                 from: "clientboughtleads",
  7.                 localField: "_id",
  8.                 foreignField: "Client",
  9.                 as: "ClientLeads"
  10.             }
  11.         },
  12.         {
  13.             $addFields: {
  14.                 TotalPurchasedLeads: {
  15.                     $size: "$ClientLeads"
  16.                 }
  17.             }
  18.         },
  19.         {
  20.             $project: {
  21.                 ClientId: "$_id",
  22.                 RegistrationDate: "$date",
  23.                 TotalPurchasedLeads: 1,
  24.                 IncomeFromClient: { // This one is always undefined
  25.                     $multiply: [LEAD_PRICE / 2, "$TotalPurchasedLeads"]
  26.                 }
  27.             }
  28.         }
  29.     ]
  30. )
英文:

Please use addFields keyword after we can use key in project .

  1.  const LEAD_PRICE  = ....; // doesn't matter 
  2.   Client.aggregate(
  3.       [
  4.         {
  5.           $lookup: {
  6.             from: "clientboughtleads",
  7.             localField: "_id",
  8.             foreignField: "Client",
  9.             as: "ClientLeads"
  10.           }
  11.         },
  12.    {
  13.      $addFields: {
  14.        TotalPurchasedLeads: {
  15.               $size: "$ClientLeads"
  16.           }
  17.      }
  18.    },
  19.         {
  20.           $project: {
  21.             ClientId: "$_id",
  22.             RegistrationDate: "$date",
  23.             TotalPurchasedLeads:1,
  24.             IncomeFromClient: {     // This one is always undefined
  25.               $multiply: [LEAD_PRICE / 2, "$TotalPurchasedLeads"]
  26.             }
  27.           }
  28.         }
  29.       ]

答案2

得分: 1

你不能在相同的 $project 阶段中使用 $project 的值。所以，改为使用其值

  1. {
  2.   "$project": {
  3.     "ClientId": "$_id",
  4.     "RegistrationDate": "$date",
  5.     "TotalPurchasedLeads": {
  6.       "$size": "$ClientLeads"
  7.     },
  8.     "IncomeFromClient": {
  9.       "$multiply": [LEAD_PRICE / 2, { "$size": "$ClientLeads" }]
  10.     }
  11.   }
  12. }
英文:

You cannot use the $projected value in the same $projection stage. So instead use its value

  1. {
  2.   "$project": {
  3.     "ClientId": "$_id",
  4.     "RegistrationDate": "$date",
  5.     "TotalPurchasedLeads": {
  6.       "$size": "$ClientLeads"
  7.     },
  8.     "IncomeFromClient": {
  9.       "$multiply": [LEAD_PRICE / 2, { "$size": "$ClientLeads" }]
  10.     }
  11.   }
  12. }

huangapple
  • 本文由 发表于 2020年1月3日 18:06:07
  • 转载请务必保留本文链接：https://go.coder-hub.com/59576585.html
  • aggregation-framework
  • mongodb
  • mongoose
  • mongoose-schema
  • node.js
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