MongoDB has encountered an error while attempting to combine two disparate conditions

Question

MongoDB has encountered an error while attempting to combine two disparate conditions

I need to run a MongoDB query using JavaScript. Specifically, I am looking to retrieve documents based on two different criteria.

The first condition is as follows:

        $or: [
          { "users.username": user.username },
          { buyer: user.username }
        ]

The second condition is:

$or: [
          { description: { $regex: req.query.q } },
          { buyer: { $regex: req.query.q } },
          { category: { $regex: req.query.q } }
        ]

To combine these two conditions into a single query, the code snippet used is:

const expenses = await db
    .collection("expenses")
    .find({
      $expr: {
        $or: [
          { "users.username": user.username },
          { buyer: user.username }
        ]
      },
      $expr: {
        $or: [
          { description: { $regex: req.query.q } },
          { buyer: { $regex: req.query.q } },
          { category: { $regex: req.query.q } }
        ],
      },
    })

However, running this query results in the following error message:

MongoServerError: Unrecognized expression '$regex'

Can anyone provide guidance on how to resolve this error? Your assistance is greatly appreciated.

javascript mongodb

Answer 1

Answer №1

It seems there may be some confusion between the mongo query language and the aggregation pipeline operators. Additionally, there appears to be an error in building the JavaScript object.

Distinguishing MQL from Aggregation Pipeline Operators

The $expr operator serves the purpose of allowing aggregation expressions within the query language, as mentioned in the documentation.

This operator permits the utilization of aggregation expressions in the query language context.

$expr is not merely a subcategory of query operators; it introduces an entirely distinct set of operators.

Illustrative examples include:

The $eq operator is specifically applicable within $expr.
References to another field's value (using $) are only valid inside $expr.
Various operators exhibit different behavior as part of aggregation than query operators do, for instance $in versus $in

While the mongo query language includes a $regex operator, no equivalent aggregation pipeline operator exists.

Aggregation employs operations like $regexFind, $regexMatch, and $regexFindAll; refer to https://www.mongodb.com/docs/manual/reference/operator/aggregation

Constructing Javascript Objects Properly

The initial argument required by the find method is a javascript object. In your code snippet, you have provided:

    {
      $expr: {$or: [
          { "users.username": user.username },
          { buyer: user.username }
      ]},
      $expr: {$or: [
          { description: { $regex: req.query.q } },
          { buyer: { $regex: req.query.q } },
          { category: { $regex: req.query.q } }
      ]}
    }

It's worth noting that this object features 2 fields bearing identical names, '$expr'. While BSON technically allows this, JavaScript/JSON prohibit such duplicate names, thereby causing the second declaration to overwrite the first.
Thus, the actual query being transmitted becomes:

    {
      $expr: {$or: [
          { description: { $regex: req.query.q } },
          { buyer: { $regex: req.query.q } },
          { category: { $regex: req.query.q } }
      ]}
    }

If you need to incorporate multiple $or clauses, they must be amalgamated using a superior-level operator, akin to:

{$and: [
      {$or: [
          { "users.username": user.username },
          { buyer: user.username }
      ]},
      {$or: [
          { description: { $regex: req.query.q } },
          { buyer: { $regex: req.query.q } },
          { category: { $regex: req.query.q } }
      ]}
]}

Answer 2

It seems there may be some confusion between the mongo query language and the aggregation pipeline operators. Additionally, there appears to be an error in building the JavaScript object.

Distinguishing MQL from Aggregation Pipeline Operators

The $expr operator serves the purpose of allowing aggregation expressions within the query language, as mentioned in the documentation.

This operator permits the utilization of aggregation expressions in the query language context.

$expr is not merely a subcategory of query operators; it introduces an entirely distinct set of operators.

Illustrative examples include:

The $eq operator is specifically applicable within $expr.
References to another field's value (using $) are only valid inside $expr.
Various operators exhibit different behavior as part of aggregation than query operators do, for instance $in versus $in

While the mongo query language includes a $regex operator, no equivalent aggregation pipeline operator exists.

Aggregation employs operations like $regexFind, $regexMatch, and $regexFindAll; refer to https://www.mongodb.com/docs/manual/reference/operator/aggregation

Constructing Javascript Objects Properly

The initial argument required by the find method is a javascript object. In your code snippet, you have provided:

    {
      $expr: {$or: [
          { "users.username": user.username },
          { buyer: user.username }
      ]},
      $expr: {$or: [
          { description: { $regex: req.query.q } },
          { buyer: { $regex: req.query.q } },
          { category: { $regex: req.query.q } }
      ]}
    }

It's worth noting that this object features 2 fields bearing identical names, '$expr'. While BSON technically allows this, JavaScript/JSON prohibit such duplicate names, thereby causing the second declaration to overwrite the first.
Thus, the actual query being transmitted becomes:

    {
      $expr: {$or: [
          { description: { $regex: req.query.q } },
          { buyer: { $regex: req.query.q } },
          { category: { $regex: req.query.q } }
      ]}
    }

If you need to incorporate multiple $or clauses, they must be amalgamated using a superior-level operator, akin to:

{$and: [
      {$or: [
          { "users.username": user.username },
          { buyer: user.username }
      ]},
      {$or: [
          { description: { $regex: req.query.q } },
          { buyer: { $regex: req.query.q } },
          { category: { $regex: req.query.q } }
      ]}
]}

MongoDB has encountered an error while attempting to combine two disparate conditions

Answer №1

Distinguishing MQL from Aggregation Pipeline Operators

Constructing Javascript Objects Properly

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