I need to convert a number field of a queried record to a string and then use that
string in a dynamic SOQL query.   If the number has a large number of digits, the
converted-to string contains an exponent (e.g.  1.321135422343E10).   If I then
do a dynamic query for records that contain that number I get an exception.

I need a way to convert the internal number to a string that never returns
an exponent in the resulting string.

Example SOQL query:
  select Name,Id,OwnerId  from Lead WHERE (mynumberfield__c = 6.9935297349E10)
 
Resulting exception:
    System.QueryException: unexpected token: 'E10'
   
Here is a simplified example othe code that converts a record field value
to a string and then uses that converted string to do a dynamic SOQL query:

  String fieldname = 'mynumberfield__c';
  sObject dRecord = [select :fieldname FROM someObject limit 1];
  Map<String, Schema.SObjectField> schemafieldmap = SSDupeCatcherutility.getSchema(objectType);        
  Schema.sObjectField sof = schemafieldmap.get(fieldname);       
  Schema.Describefieldresult dfr =   sof.getDescribe();
  Object thevalue = foundrecord.get(fieldname);
  String convertedstring = '';
  
  // convert field value to a string
  if (fieldtype == Schema.DisplayType.Double)
  {
    Decimal converted = ((Decimal) thevalue);
    convertedstring = String.valueOf(converted);
  } 
  else if (fieldtype == Schema.DisplayType.Double) 
     ..
     ..
     
  // build query that uses the converted field 
  String querystring =  'select Name,Id,OwnerId  from ' + objectType + ' WHERE (' + fieldname + ' = ' + convertedstring + ')';

Any ideas on how to convert the record value to a string that can be used in a dynamic SOQL query?

Any help would be greatly appreciated.

Thanks,

TomDJ