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.

withCount

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.

var post = getInstance( "Post" )
	.withCount( "comments" )
	.findOrFail( 1 );
	
post.getCommentsCount();

You can alias the count attribute using the AS syntax as follows:

var post = getInstance( "Post" )
	.withCount( "comments AS myCommentsCount" )
	.findOrFail( 1 );
	
post.getMyCommentsCount();

This is especially useful as you can dynamically constrain counts at runtime using the same struct syntax as eager loading with the with function.

var post = getInstance( "Post" )
	.withCount( [
	    "comments AS allCommentsCount",
	    { "comments AS pendingCommentsCount": function( q ) {
	        q.where( "approved", 0 );
	    } },
	    { "comments AS approvedCommentsCount": function( q ) {
	        q.where( "approved", 1 );
	    } }
	] )
	.findOrFail( 1 );
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post.getAllCommentsCount();	
post.getPendingCommentsCount();
post.getApprovedCommentsCount();

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