Class SystemVariables


  • public final class SystemVariables
    extends Object
    Defines helper fields for referencing system variables
    • Field Detail

      • CLUSTER_TIME

        public static final Expression CLUSTER_TIME
        A variable that returns the current timestamp value. CLUSTER_TIME is only available on replica sets and sharded clusters.

        CLUSTER_TIME returns the same value for all members of the deployment and remains the same throughout all stages of the pipeline.

      • CURRENT

        public static final Expression CURRENT
        References the start of the field path being processed in the aggregation pipeline stage. Unless documented otherwise, all stages start with CURRENT the same as ROOT.

        CURRENT is modifiable. However, since $ is equivalent to $$CURRENT., rebinding CURRENT changes the meaning of $ accesses.

      • DESCEND

        public static final Expression DESCEND
        One of the allowed results of a $redact expression.
      • KEEP

        public static final Expression KEEP
        One of the allowed results of a $redact expression.
      • NOW

        public static final Expression NOW
        A variable that returns the current datetime value. NOW returns the same value for all members of the deployment and remains the same throughout all stages of the aggregation pipeline.
      • PRUNE

        public static final Expression PRUNE
        One of the allowed results of a $redact expression.
      • REMOVE

        public static final Expression REMOVE
        A variable which evaluates to the missing value. Allows for the conditional exclusion of fields. In a $projection, a field set to the variable REMOVE is excluded from the output.

        For an example of its usage, see Conditionally Exclude Fields.

      • ROOT

        public static final Expression ROOT
        References the root document, i.e. the top-level document, currently being processed in the aggregation pipeline stage.