how to work with $lookup and $regex search in mongodb

问题

  var query = req.params.query;

    const messages = await Message.aggregate([
      {
        $lookup: {
          from: 'users',
          localField: 'reference_id',
          foreignField: '_id',
          as: 'users'
        }
      },
      {'text': {'$regex': `.*${query}.*`}}
    ])

$lookup is providing me right information but $regex is not properly working When add {'text': {'$regex': .*${query}.*}} tells me Arguments must be aggregate pipeline operators after $lookup i have data

{
    "response": {
        "messages": [
            {
                "_id": "5e4a8e640b92852e110af62f",
                "text": "Gsshha",
                "reference_id": null,
                "date": 1581944420262,
                "users": [
                    {
                        "_id": "5e4a8d2d3952132a08ae5764",
                        "phone": "1111111111",
                        "first_name": "Test1",
                        "last_name": "Test1",
                        "timestamp": 1581944109860
                    }
                ]
            },
            {
                "_id": "5e4ce3a4f55dd93292cbe149",
                "unreads": [
                "text": "Hi",
                "reference_id": null,
                "date": 1582097316013,
                "users": [
                    {
                        "_id": "5e4a8d2d3952132a08ae5764",
                        "phone": "1111111111",
                        "first_name": "Test1",
                        "last_name": "Test1",
                        "timestamp": 1581944109860
                    }
                ]
            }
        ]
    }
}

What I want to achieve get all the value from $lookup and the search string from text field, first_name field and last_name field how to achieve this

回答1:

You've syntax error in query, Try as like given below :

var query = req.params.query;

const messages = await Message.aggregate([
    {
        $lookup: {
            from: 'users',
            localField: 'reference_id',
            foreignField: '_id',
            as: 'users'
        }
    }, { $match: { 'text': { '$regex': `.*${query}.*` } } }
])

So the issue is when you get this error : Arguments must be aggregate pipeline operators, As you can see there are certain stages or operators in aggregation like Ex:- $lookup, $match, $project etc.. so if aggregate finds anything other it would throw an error. Since you need to filter data you need to wrap you piece of code 'text': { '$regex':.${query}.} in $match.

Ref : aggregation-pipeline

来源：https://stackoverflow.com/questions/60314196/how-to-work-with-lookup-and-regex-search-in-mongodb