473,698 Members | 2,923 Online
Bytes | Software Development & Data Engineering Community
+ Post

Home Posts Topics Members FAQ

Returning nulls

Whats the common/best practice for returning a "Does not exist/not
found" result from a function. Imagine I've got a function:

myObjectType GetById(long id);

where the object may or may not be found. Currently, I just return a
null. But this muddies up the calling code with null checks and stuff.
Example:
I've got an Appoinment class, that has a property Doctor of class
Doctor. This property is lazily loaded, so I only store the id of the
doctor in the Appointment class (doctor_id).

public property Doctor Doctor{
get{
if(doctor == null){doctor =
DoctorManager.G etById(doctor_i d)}
return doctor;
}
set{
doctor = value;
if(value != null){doctor_id = value.id;}
else{doctor_id = 0;}
}
}

Now, when using the Doctor property in Appointment class, I always have
to check if the Doctor is null. This can be ugly when doing something
like displaying the Appointment information.

private void showAppointment (Appointment apt){
txtTime.Text = ...
if(apt.Doctor != null){
txtRoom.Text = apt.Doctor.Offi ceNumber;
txtDoctorName.T ext = apt.Doctor.Name ;
}
etc...
}

I was thinking of creating a static Doctor instance in the Doctor class
that represents a Null Doctor like this:
public class Doctor{
public static readonly Doctor NullDoctor = new Doctor("Null
Doctor name", "Null Doctor Office",...);
...
}

and in the GetById() functions, returning the NullDoctor if none is
found. This of course, would cause me to change my Doctor Property to
something like this:
public property Doctor Doctor{
get{
if(doctor == null || doctor = Doctor.NullDoct or)
{doctor = DoctorManager.G etById(doctor_i d)}
return doctor;
}
set{
doctor = value;
if(value != null){doctor_id = value.id;}
else{doctor_id = 0;}
}
}

Pros/Cons for each approch?

Feb 16 '06 #1
1 1703
SP

<an************ *@gmail.com> wrote in message
news:11******** **************@ o13g2000cwo.goo glegroups.com.. .
Whats the common/best practice for returning a "Does not exist/not
found" result from a function. Imagine I've got a function:

myObjectType GetById(long id);

where the object may or may not be found. Currently, I just return a
null. But this muddies up the calling code with null checks and stuff.
Example:
I've got an Appoinment class, that has a property Doctor of class
Doctor. This property is lazily loaded, so I only store the id of the
doctor in the Appointment class (doctor_id).

public property Doctor Doctor{
get{
if(doctor == null){doctor =
DoctorManager.G etById(doctor_i d)}
return doctor;
}
set{
doctor = value;
if(value != null){doctor_id = value.id;}
else{doctor_id = 0;}
}
}

Now, when using the Doctor property in Appointment class, I always have
to check if the Doctor is null. This can be ugly when doing something
like displaying the Appointment information.

private void showAppointment (Appointment apt){
txtTime.Text = ...
if(apt.Doctor != null){
txtRoom.Text = apt.Doctor.Offi ceNumber;
txtDoctorName.T ext = apt.Doctor.Name ;
}
etc...
}

I was thinking of creating a static Doctor instance in the Doctor class
that represents a Null Doctor like this:
public class Doctor{
public static readonly Doctor NullDoctor = new Doctor("Null
Doctor name", "Null Doctor Office",...);
...
}

and in the GetById() functions, returning the NullDoctor if none is
found. This of course, would cause me to change my Doctor Property to
something like this:
public property Doctor Doctor{
get{
if(doctor == null || doctor = Doctor.NullDoct or)
{doctor = DoctorManager.G etById(doctor_i d)}
return doctor;
}
set{
doctor = value;
if(value != null){doctor_id = value.id;}
else{doctor_id = 0;}
}
}


Null Object is a common pattern. It encapsulates the behavior expected when
there is no object and eliminates special null handling code that is
scattered throughout your software. If implemented you would eliminate the
== null checks and either check the IsNull property or do no checking at
all. This is because the null object should act correctly, e.g. it's ID
would be 0 as that is the behavior you have decided you want with the
current "null". You will still use the == null checking for your lazy
loading as it is an indicator that no object has been created. However the
object that is created may be a real Doctor or a Null Doctor (there is no
Doctor with that ID). Therefore == null and myDoctor.IsNull are not the same
and mean very different things.

Refactoring by Martin Fowler has a few pages on this.

SP

Feb 16 '06 #2

This thread has been closed and replies have been disabled. Please start a new discussion.

Similar topics

0
1895
by: Dan Perlman | last post by:
From: "Dan Perlman" <dan@dpci.NOSPAM.us> Subject: ODBC creating nulls? Date: Friday, July 09, 2004 10:43 AM Hi, Below is my VB6 code that writes data from an Access 2000 table to a PG table. The " & "" " on the right of each line should prevent nulls from being
3
1877
by: adam | last post by:
Hello, I have a MySQL table that has (among other fields) an affiliate_id, affiliate_sub_id, and a response_code field. - affiliate_id stores the unique number of each of my affiliates. - affiliate_sub_id stores the affiliate ID of their affiliates. - response_code holds a number between 1 - 6.
3
2011
by: aaj | last post by:
Hi I am probably going to regret asking this because I'm sure you are going to tell me my design is bad 8-) ah well we all have to learn.... anyway I often use Nulls as a marker to see if certain tasks have been completed. A typical example would be a column say invoice_value
6
28292
by: mike | last post by:
I'm doing what I thought was a simple GROUP BY summary of fairly simple data and the my numbers aren't working out Some results are showing up <NULL> when I know the data is in the database I'm no SQL expert, but if I'm summing (SUM) multiple fields and adding them together in my SELECT how does SUM handle Null? In some situations a single column in a single row is Null but and it's part of a larger GROUP BY and SUM and from looking...
0
1582
by: Rhino | last post by:
I am working with SQL Functions in DB2 for Windows/Linux/UNIX (V8.2.1) and am having a problem setting input parameters for SQL Functions to null in the Development Center. My simple function, called Half, has a single integer input parameter and divides this value by two to produce its result. It also tests the input parameter to see if it is null; if it is null, it returns null. When I click the Run button and try to use the SET TO...
1
2071
by: PST | last post by:
Here's a problem I'm trying to deal with: I'm working on a Frontpage 2000 website for a boat handicapping system, built in Access 97. What I'm trying to accomplish is: The user enters a boat name in a text field OR a sail number in a text field, and gets the desired boat record back (an exact match).
6
2616
by: Josh Close | last post by:
I'm having a problem with a value coming out of a loop. CREATE OR REPLACE FUNCTION funmessagespermintotal() RETURNS int8 AS ' DECLARE this_rServer record; this_rSum record; this_iSum bigint;
0
282
by: anonymous.user0 | last post by:
Whats the common/best practice for returning a "Does not exist/not found" result from a function. Imagine I've got a function: myObjectType GetById(long id); where the object may or may not be found. Currently, I just return a null. But this muddies up the calling code with null checks and stuff. Example: I've got an Appoinment class, that has a property Doctor of class Doctor. This property is lazily loaded, so I only store the...
6
5450
by: Cliff72 | last post by:
I need to fill in the nulls in the batch field the value from the record immediately preceding the null one ie replace the nulls with the preceding value until I hit a record with a value in it--then hold the next value through the next set of nulls, and so on. See example below: I wanna copy down batch "IMR138" in record ID 1, all the way to ID 10. Then copy down batch "7138" all the way to ID 20 and so on....
0
8683
marktang
by: marktang | last post by:
ONU (Optical Network Unit) is one of the key components for providing high-speed Internet services. Its primary function is to act as an endpoint device located at the user's premises. However, people are often confused as to whether an ONU can Work As a Router. In this blog post, we’ll explore What is ONU, What Is Router, ONU & Router’s main usage, and What is the difference between ONU and Router. Let’s take a closer look ! Part I. Meaning of...
0
8610
by: Hystou | last post by:
Most computers default to English, but sometimes we require a different language, especially when relocating. Forgot to request a specific language before your computer shipped? No problem! You can effortlessly switch the default language on Windows 10 without reinstalling. I'll walk you through it. First, let's disable language synchronization. With a Microsoft account, language settings sync across devices. To prevent any complications,...
1
8902
by: Hystou | last post by:
Overview: Windows 11 and 10 have less user interface control over operating system update behaviour than previous versions of Windows. In Windows 11 and 10, there is no way to turn off the Windows Update option using the Control Panel or Settings app; it automatically checks for updates and installs any it finds, whether you like it or not. For most users, this new feature is actually very convenient. If you want to control the update process,...
0
8873
tracyyun
by: tracyyun | last post by:
Dear forum friends, With the development of smart home technology, a variety of wireless communication protocols have appeared on the market, such as Zigbee, Z-Wave, Wi-Fi, Bluetooth, etc. Each protocol has its own unique characteristics and advantages, but as a user who is planning to build a smart home system, I am a bit confused by the choice of these technologies. I'm particularly interested in Zigbee because I've heard it does some...
1
6528
isladogs
by: isladogs | last post by:
The next Access Europe User Group meeting will be on Wednesday 1 May 2024 starting at 18:00 UK time (6PM UTC+1) and finishing by 19:30 (7.30PM). In this session, we are pleased to welcome a new presenter, Adolph Dupré who will be discussing some powerful techniques for using class modules. He will explain when you may want to use classes instead of User Defined Types (UDT). For example, to manage the data in unbound forms. Adolph will...
0
5862
by: conductexam | last post by:
I have .net C# application in which I am extracting data from word file and save it in database particularly. To store word all data as it is I am converting the whole word file firstly in HTML and then checking html paragraph one by one. At the time of converting from word file to html my equations which are in the word document file was convert into image. Globals.ThisAddIn.Application.ActiveDocument.Select();...
0
4372
by: TSSRALBI | last post by:
Hello I'm a network technician in training and I need your help. I am currently learning how to create and manage the different types of VPNs and I have a question about LAN-to-LAN VPNs. The last exercise I practiced was to create a LAN-to-LAN VPN between two Pfsense firewalls, by using IPSEC protocols. I succeeded, with both firewalls in the same network. But I'm wondering if it's possible to do the same thing, with 2 Pfsense firewalls...
1
3052
by: 6302768590 | last post by:
Hai team i want code for transfer the data from one system to another through IP address by using C# our system has to for every 5mins then we have to update the data what the data is updated we have to send another system
2
2339
muto222
by: muto222 | last post by:
How can i add a mobile payment intergratation into php mysql website.

By using Bytes.com and it's services, you agree to our Privacy Policy and Terms of Use.

To disable or enable advertisements and analytics tracking please visit the manage ads & tracking page.