MongoDB聚合查询：将数组字段转换为布尔值（依据指定值是否存在）

Absolutely! You can do this with MongoDB's aggregation framework without filtering out any documents—we'll just replace the tags array with a boolean flag based on whether it contains your target value. Here's the query you need:

db.yourCollection.aggregate([
  {
    $addFields: {
      tags: { $in: ['tag that matters', '$tags'] }
    }
  }
])

Let's break down what's happening here: #

• $addFields stage: This lets us either add new fields or replace existing ones (which is exactly what we want for tags) while keeping all other document fields intact.
• $in operator: This checks if the first value ('tag that matters') exists in the array specified by the second value ($tags, our original array field). It returns true if the value is found, false otherwise—perfect for your use case.

Example Output: #

For your sample document:

{
  _id: ObjectId('604edf91571e7ab19cc2c238'),
  timestamp: 1616164767.773929,
  name: 'some name',
  metric1: 1,
  metric2: 2,
  metric3: 3,
  tags: ['tag1', 'tag2', 'tag3', 'tag that matters']
}

The result will be:

{
  _id: ObjectId('604edf91571e7ab19cc2c238'),
  timestamp: 1616164767.773929,
  name: 'some name',
  metric1: 1,
  metric2: 2,
  metric3: 3,
  tags: true
}

And for a document where tags doesn't contain 'tag that matters' (e.g., tags: ['tag1', 'tag2']), the tags field will be set to false instead—no documents are excluded from the results.

内容的提问来源于stack exchange，提问作者unltd_J