%JSON.Adaptor does not construct an intermediate dynamic object. You can use %ObjectToAET to convert normal object into dynamic object:

set dynObj = ##class(%ZEN.Auxiliary.altJSONProvider).%ObjectToAET(obj)

There are two approaches:

1. Create a "result set" class to hold the results (interestingly, InterSystems provides %XML.DataSet and other tools for this specific use case with XML/SOAP. Docs):

Class Test.JSONRS Extends (%RegisteredObject, %JSON.Adaptor)
{
Property count As %Integer;
Property results As list Of Book;
}

2. Simple approach:

• Output header {"results": 3, "items": [
• Call %JSONExport on each book (don't forget the comma at the end)
• Output footer ]}

Despite being hacky, the second approach is better:

• If JSON export on each individual object is successful it works every time and if some object fails we won't get valid a JSON anyways
• It can be easily generalized to use with any type of result
• It does not hold a large structure in memory as each object is loaded/displayed individually.

That said, I generally recommend against supplying count in query results because of many reasons:

• Users do not care for thousands of results
• It's slow - we need to know how much results there are
• Use pagination instead - if a current page has a max number of results, display the link to the next page

You'll need a Custom Function.

If the lookup field is indexed (Location in your case) you can use this function for all Lookup checks:

ClassMethod Exists(class As %Dictionary.CacheClassname, index As %String, value As %String) As %Boolean [ CodeMode = expression]
{
$classmethod(class, index _ "Exists", value)
}

You need to write an Alert Processor. Monitoring Alerts.

Does ensemble can limit request speed at Business Service?  too many requests slowdown my service.

InterSystems IRIS comes with InterSystems API Manager which is designed for these kind of tasks.

But at the message trace page. I can't found any source address .  

You can use $$$TRACE to capture additional information. Also CSP Gateway has additional request tracing facilities. Here's how you can enable tracing there.

But most importantly as I said in your previous post it looks like you're running Ensemble service on a custom port. First thing you need to do is:

• Install public web server
• Adjust web server configuration for better performance
• Connect it to Ensemble
• Switch Ensemble Business Service to use public web server