Relationship Counts
One common type of subselect field is the count of related entites. For instance, you may want to load a Post or a list of Posts with the count of Comments on each Post. You can reuse your existing relationship definitions and add this count using the withCount method.
Adds a count of related entities as a subselect property. Relationships can be constrained at runtime by passing a struct where the key is the relationship name and the value is a function to constrain the query.
By default, you will access the returned count using the relationship name appended with Count, i.e. comments will be available under commentsCount.
You can alias the count attribute using the AS syntax as follows:
This is especially useful as you can dynamically constrain counts at runtime using the same struct syntax as eager loading with the with function.