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$exists (requête d’élément)

S’APPLIQUE À : MongoDB vCore

L’opérateur $exists correspond aux documents qui ont le champ spécifié. Quand $exists c’est truele cas, il sélectionne les documents qui contiennent le champ, y compris les documents où la valeur du champ est null. Quand $exists c’est falsele cas, la requête retourne uniquement les documents qui ne contiennent pas le champ.

Syntaxe

La syntaxe de l’opérateur $exists est la suivante :

{
  <field>: { $exists: <boolean> }
}

Paramètres

Descriptif
field Champ à vérifier l’existence.
boolean true pour faire correspondre les documents qui contiennent le champ (y compris les valeurs Null), false pour faire correspondre les documents qui ne contiennent pas le champ.

Exemple :

Comprenons l’utilisation avec l’exemple JSON du jeu de stores données.

{
  "_id": "905d1939-e03a-413e-a9c4-221f74055aac",
  "name": "Trey Research | Home Office Depot - Lake Freeda",
  "location": { "lat": -48.9752, "lon": -141.6816 },
  "staff": { "employeeCount": { "fullTime": 12, "partTime": 19 } },
  "sales": {
    "salesByCategory": [ { "categoryName": "Desk Lamps", "totalSales": 37978 } ],
    "revenue": 37978
  },
  "promotionEvents": [
    {
      "eventName": "Crazy Deal Days",
      "promotionalDates": {
        "startDate": { "Year": 2023, "Month": 9, "Day": 27 },
        "endDate": { "Year": 2023, "Month": 10, "Day": 4 }
      },
      "discounts": [
        { "categoryName": "Desks", "discountPercentage": 22 },
        { "categoryName": "Filing Cabinets", "discountPercentage": 23 }
      ]
    }
  ],
  "company": "Trey Research",
  "city": "Lake Freeda",
  "storeOpeningDate": "2024-09-26T22:55:25.779Z",
  "lastUpdated": "Timestamp({ t: 1729983325, i: 1 })"
}

Exemple 1 : Rechercher des magasins avec des événements de promotion

L’exemple recherche tous les magasins qui ont des événements de promotion définis.

db.stores.find(
  { "promotionEvents": { $exists: true }},
  { "_id": 1, "promotionEvents": { $slice: 1 }}
).limit(2)

La requête retourne tous les documents où le promotionEvents champ existe, que le tableau soit vide ou contient des éléments.

  {
    "_id": "a715ab0f-4c6e-4e9d-a812-f2fab11ce0b6",
    "name": "Lakeshore Retail | Holiday Supply Hub - Marvinfort",
    "location": { "lat": -74.0427, "lon": 160.8154 },
    "staff": { "employeeCount": { "fullTime": 9, "partTime": 18 } },
    "sales": {
      "salesByCategory": [
        { "categoryName": "Stockings", "totalSales": 25731 }
      ],
      "revenue": 25731
    },
    "promotionEvents": [
      {
        "eventName": "Mega Savings Extravaganza",
        "promotionalDates": {
          "startDate": { "Year": 2023, "Month": 6, "Day": 29 },
          "endDate": { "Year": 2023, "Month": 7, "Day": 7 }
        },
        "discounts": [
          { "categoryName": "Stockings", "discountPercentage": 16 },
          { "categoryName": "Tree Ornaments", "discountPercentage": 8 }
        ]
      }
    ],
    "company": "Lakeshore Retail",
    "city": "Marvinfort",
    "storeOpeningDate": "2024-10-01T18:24:02.586Z",
    "lastUpdated": "2024-10-02T18:24:02.000Z"
  },
  {
    "_id": "923d2228-6a28-4856-ac9d-77c39eaf1800",
    "name": "Lakeshore Retail | Home Decor Hub - Franciscoton",
    "location": { "lat": 61.3945, "lon": -3.6196 },
    "staff": { "employeeCount": { "fullTime": 7, "partTime": 6 } },
    "sales": {
      "salesByCategory": [
        { "categoryName": "Lamps", "totalSales": 19880 },
        { "categoryName": "Rugs", "totalSales": 20055 }
      ],
      "revenue": 39935
    },
    "promotionEvents": [
      {
        "eventName": "Unbeatable Markdown Mania",
        "promotionalDates": {
          "startDate": { "Year": 2024, "Month": 3, "Day": 25 },
          "endDate": { "Year": 2024, "Month": 4, "Day": 1 }
        },
        "discounts": [
          { "categoryName": "Vases", "discountPercentage": 8 },
          { "categoryName": "Lamps", "discountPercentage": 5 }
        ]
      }
    ],
    "company": "Lakeshore Retail",
    "city": "Franciscoton",
    "lastUpdated": "2024-12-02T12:01:46.000Z",
    "storeOpeningDate": "2024-09-03T07:21:46.045Z"
  }

Exemple 2 : Rechercher l’existence d’un champ imbriqué

Cet exemple recherche les magasins qui ont des informations sur le nombre d’employés à temps plein.

db.stores.find(
 { "staff.employeeCount.fullTime": { $exists: true }},
 { "_id": 1, "staff.employeeCount": 1 }).limit(2)

La requête retourne les magasins où existe le champ staff.employeeCount.fullTime imbriqué.

  {
    "_id": "a715ab0f-4c6e-4e9d-a812-f2fab11ce0b6",
    "staff": {
      "employeeCount": {
        "fullTime": 9,
        "partTime": 18
      }
    }
  },
  {
    "_id": "923d2228-6a28-4856-ac9d-77c39eaf1800",
    "staff": {
      "employeeCount": {
        "fullTime": 7,
        "partTime": 6
      }
    }
  }

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