operation
public java.lang.String operation()
Gets the operation.
Identifies what type of operation to perform.
**copy** - Copies the value of the **source_field** to the **destination_field** field. If the
**destination_field** already exists, then the value of the **source_field** overwrites the original value of the
**destination_field**.
**move** - Renames (moves) the **source_field** to the **destination_field**. If the **destination_field** already
exists, then the value of the **source_field** overwrites the original value of the **destination_field**. Rename
is identical to copy, except that the **source_field** is removed after the value has been copied to the
**destination_field** (it is the same as a _copy_ followed by a _remove_).
**merge** - Merges the value of the **source_field** with the value of the **destination_field**. The
**destination_field** is converted into an array if it is not already an array, and the value of the
**source_field** is appended to the array. This operation removes the **source_field** after the merge. If the
**source_field** does not exist in the current document, then the **destination_field** is still converted into an
array (if it is not an array already). This conversion ensures the type for **destination_field** is consistent
across all documents.
**remove** - Deletes the **source_field** field. The **destination_field** is ignored for this operation.
**remove_nulls** - Removes all nested null (blank) field values from the ingested document. **source_field** and
**destination_field** are ignored by this operation because _remove_nulls_ operates on the entire ingested
document. Typically, **remove_nulls** is invoked as the last normalization operation (if it is invoked at all, it
can be time-expensive).
- Returns:
- the operation