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Specify Allowed Field Values

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Context

Steps

When you create a JSON Schema, you can specify what values are allowed in a particular field. Use this functionality to ensure that your field values belong to an expected set of values, such as a list of countries. Similarly, you can use this functionality to prevent human error, such as typos, when inserting data into a collection.

Context

To specify a list of allowed values, use the enum keyword in your JSON schema. The enum keyword means "enumerate", and is used to list possible values of a field.

Steps

Consider a clothing company that only ships products to France, the United Kingdom, and the United States. In the validator, you can list the allowed country values and reject documents that specify a different country.

Create a collection with validation containing `enum`.

Create a shipping collection and use the $jsonSchema operator to set schema validation rules:

db.createCollection("shipping", {
   validator: {
      $jsonSchema: {
         bsonType: "object",
         title: "Shipping Country Validation",
         properties: {
            country: {
               enum: [ "France", "United Kingdom", "United States" ],
               description: "Must be either France, United Kingdom, or United States"
            }
         }
      }
   }
} )

The enum field in the country object only allows documents where the country field is either France, United Kingdom, or United States.

Confirm that the validation prevents invalid documents.

The following insert operation fails because country is Germany, which isn't in the list of allowed values.

db.shipping.insertOne( {
   item: "sweater",
   size: "medium",
   country: "Germany"
} )

The operation returns this error:

MongoServerError: Document failed validation
Additional information: {
  failingDocumentId: ObjectId("630d1057931191850b40d0aa"),
  details: {
    operatorName: '$jsonSchema',
    title: 'Shipping Country Validation',
    schemaRulesNotSatisfied: [
      {
        operatorName: 'properties',
        propertiesNotSatisfied: [
          {
            propertyName: 'country',
            description: 'Must be either France, United Kingdom, or United States',
            details: [
              {
                operatorName: 'enum',
                specifiedAs: {
                  enum: [ 'France', 'United Kingdom', 'United States' ]
                },
                reason: 'value was not found in enum',
                consideredValue: 'Germany'
              }
            ]
          }
        ]
      }
    ]
  }
}

Insert a valid document.

The insert succeeds after you change the country field to one of the allowed values:

db.shipping.insertOne( {
   item: "sweater",
   size: "medium",
   country: "France"
} )

Query for the valid document.

To confirm that the document was successfully inserted, query the shipping collection:

db.shipping.find()

MongoDB returns the document:

[
  {
    _id: ObjectId("630d10d5931191850b40d0ab"),
    item: 'sweater',
    size: 'medium',
    country: 'France'
  }
]

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