code: public OQueryContextNative contains(final Object iKey) {
  		if (finalResult != null && finalResult.booleanValue())
  			return this;
  
  		if (iKey == null)
  			// ERROR: BREAK CHAIN
  			return error();
  
  		if (currentValue != null)
  			if (currentValue instanceof Map)
  				currentValue = ((Map<Object, Object>) currentValue).containsKey(iKey);
  			else if (currentValue instanceof Collection)
  				currentValue = ((Collection<Object>) currentValue).contains(iKey);
  			else if (currentValue instanceof ODocument)
  				currentValue = ((ODocument) currentValue).containsField(iKey.toString());
  
  		return this;
  	}
docs: Sets as current value TRUE if the key exists, otherwise FALSE. For Maps and Collections the contains() method is called.
  Against Documents containsField() is invoked.
  
  
  @param iKey
  Key to use for the lookup
  @return This object to allow fluent expressions in chain.