Calculating Results On-The-Fly with Virtual Fields

Virtual fields allow you to compute values from many elements of the Exalead CloudView index. The main purpose of a virtual field is to access stored index fields.

For example, a virtual field called revenue with expression price * quantity accesses the two fields and calculate the total price.

This page discusses:

See Also
Calculate Distances in Virtual Fields
Reusing Ranking Elements in Virtual Fields

When to Use Virtual Fields

You can use virtual fields for multiple areas within your search application. For example, for a given hit, virtual fields can calculate:

  • A meta to display in the search client.

  • The value for the hit in a dynamic numerical facet (see below).

  • The value for the hit in a facet aggregation (see below).

  • Ranking elements (see below).

  • A value to use for filtering queries.

    For example, you can define a numerical prefix handler, total_price, allowing a user to queries directly on the total price, such as. total_price: > 500.

Performance Considerations

Virtual fields have a significant overhead at query time, because of the evaluation that must take place for each hit.

In some cases, this evaluation must absolutely be performed at query time.

For example, if your geographic expression calculates the distance between a hit and the current position of the user, then it is fully contextual to the query. However, if you find yourself using a large number of virtual fields with totally static expressions that are always used, it can be a good compromise to precompute them using processors in the analysis pipeline.