BSON Types

    BSONis a binary serialization format used to store documents and make remote procedure calls in MongoDB. The BSON specification is located at.

    Each BSON type has both integer and string identifiers as listed in the following table:

    You can use these values with theoperator to query documents by their BSON type. Theaggregation operator returns the type of anoperator expressionusing one of the listed BSON type strings.

    To determine a field’s type, see.

    If you convert BSON to JSON, see theExtended JSONreference.

    The following sections describe special considerations for particular BSON types.

    ObjectIds are small, likely unique, fast to generate, and ordered. ObjectId values consist of 12 bytes, where the first four bytes are a timestamp that reflect the ObjectId’s creation. Specifically:

    • a 4-byte value representing the seconds since the Unix epoch,
    • a 3-byte machine identifier,
    • a 2-byte process id, and
    • a 3-byte counter, starting with a random value.

    In MongoDB, each document stored in a collection requires a uniquefield that acts as aprimary key. If an inserted document omits the_idfield, the MongoDB driver automatically generates anfor the_idfield.

    This also applies to documents inserted through update operations withupsert: true.

    MongoDB clients should add an_idfield with a unique ObjectId. Using ObjectIds for the_idfield provides the following additional benefits:

    SEE ALSO

    BSON strings are UTF-8. In general, drivers for each programming language convert from the language’s string format to UTF-8 when serializing and deserializing BSON. This makes it possible to store most international characters in BSON strings with ease.[1]In addition, MongoDBqueries support UTF-8 in the regex string.

    [1] Given strings using UTF-8 character sets, usingon strings will be reasonably correct. However, because internallysort()uses the C++strcmpapi, the sort order may handle some characters incorrectly.

    BSON has a special timestamp type for_internal_MongoDB use and isnotassociated with the regulartype. Timestamp values are a 64 bit value where:

    • the first 32 bits are a
      time_t
      value (seconds since the Unix epoch)
    • the second 32 bits are an incrementing

      for operations within a given second.

    Within a singlemongodinstance, timestamp values are always unique.

    In replication, thehas atsfield. The values in this field reflect the operation time, which uses a BSON timestamp value.

    NOTE

    The BSON timestamp type is for_internal_MongoDB use. For most cases, in application development, you will want to use the BSON date type. SeeDatefor more information.

    If you insert a document containing an empty BSON timestamp in a top-level field, the MongoDB server will replace that empty timestamp with the current timestamp value. For example, if you create an insert a document with a timestamp value, as in the following operation:

    Then, theoperation will return a document that resembles the following:

    1. {
    2. "_id"
    3. :
    4. ObjectId
    5. (
    6. "542c2b97bac0595474108b48"
    7. ),
    8. "ts"
    9. :
    10. Timestamp
    11. (
    12. ,
    13. 1
    14. )
    15. }

    Ifwere a field in an embedded document, the server would have left it as an empty timestamp value.

    BSON Date is a 64-bit integer that represents the number of milliseconds since the Unix epoch (Jan 1, 1970). This results in a representable date range of about 290 million years into the past and future.

    Theofficial BSON specificationrefers to the BSON Date type as theUTC datetime.

    BSON Date type is signed.Negative values represent dates before 1970.

    EXAMPLE

    Construct a Date using thenewDate()constructor in themongoshell:

    EXAMPLE

    Construct a Date using theISODate()constructor in theshell:

    1. var
    2. mydate2
    3. =
    4. ISODate
    5. ()

    EXAMPLE

    Return theDatevalue as string:

    EXAMPLE

    Return the month portion of the Date value; months are zero-indexed, so that January is month0:

    1. mydate1
    2. .
    3. getMonth
    4. ()

    | [2] | Prior to version 2.0,Datevalues were incorrectly interpreted as_unsigned_integers, which affected sorts, range queries, and indexes onDatefields. Because indexes are not recreated when upgrading, please re-index if you created an index onDatevalues with an earlier version, and dates before 1970 are relevant to your application. |
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