如何将数组中存在的值与mongo中的字段进行匹配

Question

I have this data set in mongo

{
  _id: {
    question_id: 3
  },
  data: {
    answer: 11,
    count: 114,
    result: [
      {
        _id: 3,
        question: "What is your age group?",
        options: [
          {
            id: 10,
            option: "<18"
          },
          {
            id: 11,
            option: "18-24"
          },
          {
            id: 12,
            option: "24-35"
          },
          {
            id: 13,
            option: ">35"
          }
        ],
        type: "Radio"
      }
    ]
  }
},

Here i would like to perform an equals to check between answer and result.options.id and if the value matches it should return result.options.option

So that the desired result is

{
  _id: {
    question_id: 3
  },
  data: {
    answer:'18-24',
    count: 114,
    
  }
},

So far i have tried this

'$project'=>[
  'res'=>[
    '$map'=>[
      'input'=>'$data.result.options',
      'as'=>'dt',
      'in'=>[
        '$cond'=>[
          'if'=>[
            '$eq'=>[
              '$$dt.id',
              '$data.answer'
            ]
          ],
          'then'=>'$$dt.option',
          'else'=>'$$dt.id'
        ]
      ]
    ]
  ]
]

Any clue as to what i am doing wrong . My code always returns the else statement

</div>

Answer 1

You were close, but there are a couple of things not quite right:

[ '$project'=> [
  'data' => [
    'answer' => [
      '$let' => [
        'vars' => [
          'res' => [
            '$reduce' => [
              'input' => '$data.result.options',
              'initialValue' => [],
              'in' => [ '$concatArrays': [ '$$value', '$$this' ] ]
            ]
          ]
        ],
        'in' => [
          '$arrayElemAt' => [
            '$$res.option',
            [ '$indexOfArray': [ '$$res.id', '$data.answer' ] ]
          ]
        ]
      ]
    ],
    'count' => '$data.count'
  ]
]]

The path to '$data.result.options' is actually within nested arrays, so in order for any "array operations" to work in the inner value of the 'options' you need to "flatten" that array structure into a singular array.

In order to do that you would use $reduce along with $concatArrays. This is also demonstrated in a $let block, since you want to use this "result array" in some later operations.

That being the most simple way to extract a single value is to find the matching index of the array via $indexOfArray to 'data.answer' and then extract the 'option' value from your "result array" processed earlier for that value using $arrayElemAt of course pointing at that matched "index".

The $indexOfArray operator is reliable here as long as you will always have an answer matching the 'data.answer' value present within the document array.