Unable to a build an apex query string

Question

I have a string where object names are enclosed in <>. Something like this->

         String source = 'I have <name> and <id>'; 

Object name is stored in another String ->

          String objectName = 'Contact'; 

I need to get the fields like this->

          String fields = 'name,id';    

How to achieve this?

So that I can use it in query ->

           String query = 'Select '+fields+' from '+objectName;
           List<sObject> myList= Database.Query(query);

Answer 1

There may be more efficient ways of doing this, but how about something like:

String source = 'I have <name> and <id>';     
Matcher m = Pattern.compile('(?m)<.*?>').matcher(source);
while (m.find()) 
{
    System.debug( source.substring(m.start()+1, m.end()-1 ) );
}

Answer 2

You could use a regular expression to realize the list of fields:

Matcher m = Pattern.compile('<([a-zA-Z0-9_]+?)>').matcher(source);
Set<String> fields = new Set<String>();
for(Integer groupNum = 1; groupNum < m.groupCount(); groupNum++) {
    fields.add(m.group(groupNum));
}
fields.retainAll(Schema.getGlobalDescribe().get(objectName).getDescribe().fields.getMap().keySEt());
String queryFields = String.join(new List<String>(fields), ',');