Supported Operations for Queryable Encryption

Operations Using BinData

MongoDB stores Queryable Encryption encrypted fields as a BinData blob. Read and write operations issued against the encrypted BinData value may have unexpected or incorrect behavior as compared to issuing that same operation against the decrypted value. Certain operations have strict BSON type support where issuing them against a BinData value returns an error. Official drivers compatible with Queryable Encryption parse read and write operations for operators or expressions that do not support BinData values or that have abnormal behavior when issued against BinData values.

Applications using explicit encryption may use this page as guidance for issuing read and write operations against encrypted fields.

Supported Read and Write Commands

Queryable Encryption compatible drivers support automatic encryption with the following commands:

• aggregate

• count

• delete

• explain

• find

• findAndModify

• insert

• update

For any supported command, the drivers return an error if the command uses an unsupported operator, aggregation stage, or aggregation expression. For a complete list of the supported operators, stages, and expressions, see the following sections:

• Supported Query Operators

• Supported Update Operators

• Supported Aggregation Stages

• Supported Aggregation Expressions

The following commands do not require automatic encryption. Official drivers configured for Automatic Encryption pass these commands directly to the mongod:

• getMore [1]

• authenticate

• hello

• logout

• abortTransaction

• commitTransaction

• endSessions

• startSession

• create

• createIndexes

• drop

• dropDatabase

• dropIndexes

• killCursors

• listCollections

• listDatabases

• listIndexes

• renameCollection

• ping

Issuing any other command through a compatible driver configured for automatic encryption returns an error.

Supported Query Operators

Drivers configured for automatic encryption support the following query operators when issued against an encrypted queryable field:

• $eq

• $ne

• $in

• $nin

• $and

• $or

• $not

• $nor

{$expr: {$eq: ["$encrypted1", "$encrypted2"]}}

{$expr: {$eq: ["$encrypted1", "plaintext_value"]}}

Queries that compare an encrypted field to null or a regular expression always throw an error, even if using a supported query operator.

The $exists operator has normal behavior when issued against encrypted fields.

Queries specifying any other query operator against an encrypted field return an error. The following query operators throw an error even if not issued against an encrypted field when using a MongoClient configured for Queryable Encryption:

• $text

• $where

• $jsonSchema

Supported Update Operators

Drivers configured for automatic encryption support the following update operators when issued against encrypted fields:

• $set

• $unset

Updates specifying any other update operator against an encrypted field return an error.

Update operations with the following behavior throw an error even if using a supported operator:

• The update operation produces an array inside of an encrypted path.

• The update operation uses aggregation expression syntax.

For update operations specifying a query filter on encrypted fields, the query filter must use only supported operators on those fields.

Replacement-style Updates

Replacement-style updates are supported, however, if the replacement document contains a Timestamp(0,0) inside a top-level encrypted field, Queryable Encryption will error. The (0,0) value indicates that the mongod should generate the Timestamp. mongod cannot generate encrypted fields.

Unsupported Insert Operations

Compatible drivers configured for automatic encryption do not support insert commands with the following behavior:

• Inserting a document with Timestamp(0,0) associated to an encrypted field. The (0,0) value indicates that the mongod should generate the Timestamp. Since the mongod cannot generate encrypted fields, the resulting timestamp would be unencrypted.

• Inserting a document without an encrypted _id if the configured automatic schema specifies an encrypted _id field. Since the mongod autogenerates an unencrypted ObjectId, omitting _id from documents results in documents that do not conform to the automatic encryption rules.

Unsupported Aggregation Stages

Automatic encryption will not support aggregation stages that read from or write to additional collections. These stages are:

• $out

• $merge

Supported Aggregation Stages

Compatible drivers configured for automatic encryption support the following aggregation pipeline stages:

• $addFields

• $bucket

• $bucketAuto

• $collStats

• $count

• $geoNear

• $group on unencrypted fields

• $indexStats

• $limit

• $lookup and $graphLookup (For usage requirements, see $lookup and $graphLookup Behavior)

• $match

• $project

• $redact

• $replaceRoot

• $sample

• $skip

• $sort

• $sortByCount

• $unwind

Aggregation pipelines operating on collections configured for automatic encryption that specify any other stage return an error.

For each supported pipeline stage, MongoDB tracks fields that must be encrypted as they pass through the supported pipelines and marks them for encryption.

Each supported stage must specify only supported query operators and aggregation expressions.

Supported Aggregation Expressions

Compatible drivers configured for automatic encryption support the following expressions against any equality query type encrypted fields:

• $cond

• $eq

• $ifNull

• $in

• $let

• $literal

• $ne

• $switch

All other aggregation expressions return an error if issued against encrypted fields.

Aggregation stages with the following behavior return an error even if using a supported aggregation expression:

$addFields : {
  "valueWithUnknownEncryption" : {
    $cond : {
      if : { "$encryptedField" : "value" },
      then : "$encryptedField",
      else: "unencryptedValue"
    }
  }
},
{
  $match : {
    "valueWithUnknownEncryption" : "someNewValue"
  }
}

{
  $eq : [
    {"newField" : "$encryptedField"},
    {"newField" : "value"
  ]
}

{ $eq : [ "$prefixOfEncryptedField" , "value"] }

{
  $eq : [
      "$encryptedField" ,
      { $ne : [ "field", "value" ] }
  ]
}

{
  $let: {
    "vars" : {
      "newVariable" : "$encryptedField"
    }
  }
}

{
  $in : [
    "$encryptedField" ,
    "$otherEncryptedField"
  ]
}

Unsupported Field Types

Drivers configured for automatic encryption do not support any read or write operation that requires encrypting the following value types:

• MaxKey

• MinKey

• null

• undefined

Queryable Encryption does not adequately hide the type information for these values.

Queryable Encryption does not support read or write operations on an encrypted field where the operation compares the encrypted field to the following value types:

• array

• decimal128

• double

• object