Package org.apache.druid.segment.transform

Interface Transform

All Known Implementing Classes:
ExpressionTransform
public interface Transform
A row transform that is part of a TransformSpec. Transforms allow adding new fields to input rows. Each one has a "name" (the name of the new field) which can be referred to by DimensionSpecs, AggregatorFactories, etc. Each also has a "row function", which produces values for this new field based on looking at the entire input row. If a transform has the same name as a field in an input row, then it will shadow the original field. Transforms that shadow fields may still refer to the fields they shadow. This can be used to transform a field "in-place". Transforms do have some limitations. They can only refer to fields present in the actual input rows; in particular, they cannot refer to other transforms. And they cannot remove fields, only add them. However, they can shadow a field with another field containing all nulls, which will act similarly to removing the field.

  • Method Summary

    Modifier and Type
    Method
    Description
    String
    getName()
    Returns the field name for this transform.
    Set<String>
    getRequiredColumns()
    Returns the names of all columns that this transform is going to read.
    RowFunction
    getRowFunction()
    Returns the function for this transform.

  • Method Details

    • getName

      String getName()
      Returns the field name for this transform.

    • getRowFunction

      RowFunction getRowFunction()
      Returns the function for this transform. The RowFunction takes an entire row as input and returns a column value as output.

    • getRequiredColumns

      Set<String> getRequiredColumns()
      Returns the names of all columns that this transform is going to read.