jump()

`jump()`

The jump() method is a convenient interface to inner_join(), for times when the left-hand query's contribution to the output is not required.

For any queries l, r, you can call l.jump(r, condition) provided that:

condition is an abstract_mapper<bool> (in practice it will be a predicate).

l and r's value mappers will both be visible to condition.

l.jump(r, condition) returns a query with the following characteristics:

Its value type is the same as r's.
Its value mapper is identical to r's.
Its output is as if formed by the following process: take the sequence of l's outputs, and replace each item lo by all of r's outputs ro such that condition evaluates to true using the values lo and ro.

l.jump(r, condition) is interchangeable with l.inner_join(r, condition).select(*r), which has exactly the same characteristics.

Example

const query<movie> movies_being_screened =
    screens.jump(movies, screens->current_movie_id == movies->id);