existsQuery¶
Query entity data stored in storage ( e.g. RDBMS, cache etc ).
This function is meant for relatively simple existence queries. For complex multi-stage queries
a service with its custom implementation will be more suitable.
Given entity types are stored based on a key, a existsQuery function will interrogate a store containing
entity type objects and apply a filter.
The existsQuery function is almost identical to the filter function, apart from the 1st argument being an
entity type instead of a vector type. The 2nd argument applies a lambda expression returning a boolean
that is used as the filter criteria.
Parameters:
| No. | Type | Comments |
|---|---|---|
| 1 | entity | The entity type being queried |
| 2 | A lambda that accepts an entity and returns a boolean | The input entity type is that of the 1st argument |
Returns:
A boolean result if the query found any objects.
Usages:
existsQuery( T, e => boolean-expression ) : boolean