Or with If and In mongodb

Question

{
  $cond: {
    if: { $in: [`$$${field.fieldName}`, ['', null]] },
    then: [],
    else: `$$${field.fieldName}`,
  },
},

In this condition, I also want to check the field.fieldName exits.

$exists: true,

then it will something like

if ( !filed.fieldName || field.fieldName === null || field.fieldName === '') then []

I am not finding any way to add $exits: true or false in this. Please help if can add something to this. Or any alternate way to achieve ?

Answer 1

You just need to put $ifNull in else part, if it's not exists it will return [],

{
  $cond: {
    if: {
      $in: [`$$${field.fieldName}`, ["", null]]
    },
    then: [],
    else: { $ifNull: [`$$${field.fieldName}`, []] }
  }
}

Playground

Input:

[
  { "key": null },
  { "key": "" },
  { "A": "a" }
]

Result:

[
  {
    "key": null,
    "status": []
  },
  {
    "key": "",
    "status": []
  },
  {
    "status": []
  }
]

---

Second approach, if you want to add an existing condition in if part you can try condition with $or,

• $type will return the field's data type the missing field type is "missing"

{
  $cond: {
    if: {
      $or: [
        { $eq: [{ $type: `$$${field.fieldName}` }, "missing"] },
        { $in: [`$$${field.fieldName}`, ["", null]] }
      ]
    },
    then: [],
    else: `$$${field.fieldName}`
  }
}

Playground