MongoDB 让变量在管道聚合中不起作用

Question

Hi I am trying to use a variable that I defined in let to be used in the match lookup, but it returns no results when regex is used:

It works like this:

db.MSP_Prosper.aggregate([
    { $match: {Cleavage_score: {$gte:0.7}}},
    { $lookup: {
      from:"Uniprot_New_Entries",
      let: { order_item: new RegExp('.*' + "P62258" + '.*')},
      pipeline: [{
        $match: { Uniprot_AC : new RegExp('.*' + "P62258" + '.*')                                      
      }},
      { $project: { _id: 0,
        test: "$$order_item",
        date: { name: "$Uniprot_ID",
        date: "$Min_Max_Of_the_Ft_chain"} 
      }
    }],
       as:"cleavage_sites"
    }   
 }

])

but not when I try to use same variable defined in let function:

db.MSP_Prosper.aggregate([
    {$match: {Cleavage_score: {$gte:0.7}}},
    {
    $lookup: { from:"Uniprot_New_Entries",
           let: { order_item: new RegExp('.*' + "P62258" + '.*')},
           pipeline: [
             { $match: 
               { Uniprot_AC : "$$order_item" }
             },
             { $project: { _id: 0,
                  test: "$$order_item",
                  date: { name: "$Uniprot_ID",
                          date: "$Min_Max_Of_the_Ft_chain"} 
             }},    
           ],
           as:"cleavage_sites"
    }   
  }
])

Ultimatelly I want to replcae the "P62258" with a local variable $Protein_ID

Hope you can help, Have tried out everything with no success.

Answer 1

The new RegExp is evaluated in the client and included in the query as an absolute value, so you cannot include a document-dependent variable that way.

To use a document field as a regular expression inside of a lookup pipeline, you will need to use a $expr clause with the $regexMatch aggregation operator. Note that the .* before and after the search string are implied, and therefore unnecessary.

Something like:

db.MSP_Prosper.aggregate([
  { $match: { Cleavage_score: { $gte: 0.7 } } },
  { $lookup: {
      from: "Uniprot_New_Entries",
      let: { "order_item": "$Protein_ID" },
      pipeline: [
        {$match: {
            $expr: {
              $regexMatch: {
                input: "$Uniprot_AC",
                regex: "$$order_item"
        }}}},
        {$project: {
            _id: 0,
            test: "$$order_item",
            date: {
              name: "$Uniprot_ID",
              date: "$Min_Max_Of_the_Ft_chain"
        }}},
      ],
      as: "cleavage_sites"
  }}
])

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