@Experimental public interface ProjectionProducer<T>
Typically this interface will be implemented by a reader
PTransform or some component thereof that is capable of pushing
down a projection to an external source.
|Modifier and Type||Method and Description|
Actuate a projection pushdown.
thissupports projection pushdown.
T actuateProjectionPushdown(java.util.Map<TupleTag<?>,FieldAccessDescriptor> outputFields)
outputFields- Map keyed by the
TupleTagfor each output on which pushdown is requested. The value is the
FieldAccessDescriptorcontaining the list of fields needed for that output; fields not present in the descriptor should be dropped.
Tthat implements the projection pushdown. The return value is assumed to be a drop-in replacement for
this; it must have all the same functionality. For this reason,
Tis usually the same class as