Shahzad Bhatti

June 15, 2009

My plan B for being a programmer

Filed under: Computing — admin @ 11:29 am

I came across an interesting blog on Programmers: Before you turn 40, get a plan B, where the author sites age discrimination in programming career. The author shows how in IT industry, technology shift every 10 years levels the plainfield so there is a little difference between junior and senior programmer. The author also asserts that more experienced programmer will have a lot of irrelevent experience that employer may not be willing to consider when hiring or may not pay higher salary for those skills. I have been programming for over twenty two years and working professionally for over seventeen years and I certainly have seen effects of technology shift. In early 90s, I worked for a physics lab that had plenty of VAX computers using FORTRAN, and they were migrating most of the system to UNIX so people with VMS skills had to adopt to UNIX. I then had to work on mainframe system for another company and used COBOL and CICS. I saw plenty of people who worked on mainframe system for over 10-15 years and knew a little outside mainframe technology. When that company also migrated to NT and UNIX platform, it was quite stressful to many people. Though, there are still companies who are willing to pay top dollars for mainframe experience but opportunities are very few. I myself had to adopt and learn C++ and object-oriented design and found other opportunties that used those skills. I was young and unmarried so switching to another technology was not hard. In mid 90s I switched to Java, CORBA and Web development and there was some learning and adopting involved. In late 90s and early 2000s, I started using Java Enterprise Beans (EJBs) and SOAP based Web services. From 2003-onward, I started using more open source technologies like Spring, Hibernate, Tomcat, REST, etc and I had to abandoned my past CORBA or EJB expertise. This was followed by rise of dynamic languages and I started using Ruby on Rails and built a couple of sites using it. After that I became interested functional programming such as Erlang. These days, I have been spending my spare time in iPhone development.

I completely agree that in programming career, the past experience becomes irrelevant and most companies won’t pay me for the irrelevant experience such as VMS, mainframe, CORBA or EJBs. Also, as I became older and started family, switching jobs just for technology became a lot harder. I believe experienced programmers who have worked with varied technologies bring useful perspective and a bit of pessimism that is often needed. I also believe most experienced programmers have better design skills and pay more attention to writing maintainable or scalable code, but it probably doesn’t matter in may places that just want to get shit done.

Another aspect that differentiates programming career from other professions is lack of predictability. I have found that in our industry, project scope, requirements and estimates are poorly defined and most companies expect programmers to be heros or martyrs who will abandoned their life and dedicate completely to the work. IT people also have to pay for the global culture of 24×7 service and have to be oncall when things break. This becomes a lot harder with the family so many companies prefer young and unmarried folks who are more willing to be heros and those young programmers like the extra attention.

So what is my plan B? It is to continually learn new skills and be a little better than the competition. Many of my past colleagues have moved to the dark site and now are directors or senior managers at other companies. And truth is that in most companies managers carry more respect and authority so no wonder most programmers aspire to become one. I on the other hand, just can’t give up programming and usually spend my spare time on a number of small projects. So I will continue to be a lowly code monkey for the rest of my life.

June 13, 2009

ActiveObject based O/R Mapping library for iPhone development

Filed under: iPhone development — admin @ 6:38 pm

I have been learning iPhone development lately and needed to add some persistence capability to my application. There are varied options available for persistence such as using “User Defaults” for small user specific settings, serialization similar to serialization or pickle features of other languages and builtin support of embeded Sqlite. I found Sqlite more performant, memory efficient and flexible than other options so I chose it. Using Sqlite with iPhone is fairly straight forward and there are tons of examples such Creating Todo list using Sqlite. However, when I looked for some O/R mapping framework for iPhone, I found that iPhone SDK unlike Mac development didn’t have any support and neither I could find any other solution elsewhere. So, I started writing a simple O/R mapping library based on Active Object pattern. This is similar to how Rails and Django implement O/R mapping. Based on convention over configuration, it simply maps object properties to the database table fields. At this time, this is very basic O/R mapping library and does not support relations, validation, database integrity support, etc. Nevertheless, it met my simple needs and I have released it as open source project under OCActiveObjects on GitHub.

The OCActiveObjects library is fairly small and consists of following classes:

ActiveObject

This is the base class that you extend in order to add automatic O/R support. You have to override following Class methods to specify name of the database and table:

     + (NSString *) getTableName;
   

Above method defines name of table where instances of the object will be stored.

     + (NSString *) getDatabaseName;
   

Above method defines name of the database to be used. You will then be able to call following methods to interact with the Sqlite database:

   + (void) openDatabase;
   

Above method must be called once before any other methods, usually at the start of your application.

   + (void) closeDatabase;
   

Above method must be called once before you shutodnw your application.

  
   - (void) save;
 

Above method saves a new object or updates an existing object. Each subclass of ActiveObject is automatically assigned a unique database id with a property
named “objectId”. This is another example of convention where all tables will use a numeric surrogate key to identify each row.
If that property is nil then it assumes this is new object and inserts a new row in the database, otherwise it updates an existing row in the
database. It assumes that name of database fields are same as property names, though you can override that behavior by overriding _getPropertyNamesAndTypes Class method.

   + (ActiveObject *) findByPrimaryKey:(NSNumber *)objId;
 

Above method queries an object in the database matching objectId property, which identifies each object in the database.

   + (NSArray *) findWithCriteria:(NSDictionary *)criteria;
 

Above method returns an array of objects that match criteria. The criteria at this time is simple dictionary, i.e., pair of name and values that are joined by
“AND” clause. There is a immediate need to extend this to support more flexible queries.

   + (NSArray *) findAll;
 

Above method returns all objects, which may not be good for iPhone application due to limited amount of memory. This is another area that needs immediate attention.

   + (int) removeAll;
 

Above method removes all rows in the table so be careful with this.

   + (int) removeWithCriteria:(NSDictionary *)criteria;
 

Above method removes only methods matching criteria. Again criteria consists of name/value pairs.

   + (int) countWithCriteria:(NSDictionary *)criteria;
 

Above method counts the number of rows in the database matching criteria.

   + (int) countAll;
 

Above method returns count of all rows in the table.

Exension Methods in ActiveObject

There are number of extension methods to customize SQLs or behavior of the object such as

 - (void) _insert;
 

Above method inserts an object into the database.

 - (void) _update;
 

Above method updates an existing object into the database.

 + (NSDictionary *) _getPropertyNamesAndTypes;
 

You can override above method to change properties that needs to be persisted.

 + (NSString *) _getCreateSQL;
 

Above method generates an SQL for creating table.

 + (NSMutableString *) _getInsertSQL;
 

Above method generates an SQL for inserting a row in the table.

 + (NSMutableString *) _getUpdateSQL;
 

Above method generates an SQL for updating a row in the table.

 + (NSMutableString *) _getSelectSQL;
 

Above method generates an SQL for selecting fields from the database.

 + (void) _createTable;
 

Above method creates database table.

IntrospectHelper

The OCActiveObjects library uses some Objective C magical runtime support to query for properties and this class encapsulates those methods.

SqliteHelper

This class some helper methods for Sqlite3.

How to use

In order to test it, let’s define a simple Person class that extends ActiveObject, e.g.

 #import <Foundation/Foundation.h>
 #import "ActiveObject.h"
 
 @interface Person : ActiveObject {
         NSString *name;
         short age;
         int rank;
         long votes;
         char sex;
         double income;
         BOOL active;
         NSInteger flags;
         NSNumber *rating;
         NSDate *birthdate;      
 }
 
 
 @property (nonatomic, retain) NSString *name;
 @property (nonatomic, assign) short age;
 @property (nonatomic, assign) int rank;
 @property (nonatomic, assign) long votes;
 @property (nonatomic, assign) char sex;
 @property (nonatomic, assign) double income;
 @property (nonatomic, assign) BOOL active;
 @property (nonatomic, assign) NSInteger flags;
 @property (nonatomic, retain) NSNumber *rating;
 @property (nonatomic, retain) NSDate *birthdate;
 
 - (BOOL)isEqualToPerson:(Person *)aPerson;
 
 @end
 

Implemention of Person.m looks like:

 #import "Person.h"
 
 @implementation Person
 @synthesize name;
 @synthesize age;
 @synthesize rank;
 @synthesize votes;
 @synthesize sex;
 @synthesize income;
 @synthesize active;
 @synthesize flags;
 @synthesize rating;
 @synthesize birthdate;
 
 - (BOOL)isEqual:(id)other {
     if (other == self)
         return YES;
     if (!other || ![other isKindOfClass:[self class]])
         return NO;
     return [self isEqualToPerson:other];
 }
 
 - (BOOL)isEqualToPerson:(Person *)aPerson {
         if (self == aPerson)
         return YES;
     if (![(id)[self name] isEqual:[aPerson name]])
         return NO;
     return YES;
 }
 
 - (NSUInteger)hash {
         NSUInteger hash = 0;
         hash += [[self name] hash];
         return hash;
 }
 
 
 
 - (NSString *)description {
         return [NSString stringWithFormat:@"id %@, name %@", self.objectId, self.name);
 }
 
 
 - (void) dealloc {
         [name release];
         [birthdate release];
         [super dealloc];
 }
 
 + (NSString *) getTableName {
         return @"persons";
 }
 
 + (NSString *) getDatabaseName {
         return @"personsdb";
 }
 
 @end
 

Then you can first open the database, e.g.

 
         [Person openDatabase];
 

Then create a new person object, e.g.

         Person *person = [[[Person alloc] init] autorelease];
         person.birthdate = [[NSDate alloc]init];
         int random = [person.birthdate timeIntervalSince1970];
         person.age =  random % 30;
         person.rank = random % 20;
         person.votes = random % 10;
         person.sex = 'M';
         person.name = [NSString stringWithFormat:@"Joe #%d", random % 1000];
         person.income = random % 3000;
         person.active = YES;
         person.flags = random % 30 + 0.5;
         person.rating = [NSNumber numberWithInt:20.5];  
         return person;
 

You will then be able to save the person object as

         [person save];
 

You can see how many rows are in the database by

         int count = [Person countAll];
 

And then retrieve the object that we saved as

         Person *person2 = (Person *) [Person findByPrimaryKey:person.objectId];
 

When you are done, you can then close the database:

         [Person closeDatabase];
 

One of the frustrating aspect of iPhone development has been lack of good unit testing support. Though, XCode comes with OCUnit, but it is hard to install and use with iPhone. I kept getting weird errors like:

 exited abnormally with code 139
 
 failed tests for architecture 'i386'
 

Though, there are some basic tutorials like Test Driving Your Code with OCUnit or OCUnit: Integrated Unit Testing In Xcode, but they didn’t help. I also tried adding google-toolbox-for-mac but macro errors are extremely frustrating. Besides better testing, OCActiveObjects needs a lot of help to add better support of criteria, paging, relational mapping and validation. I also had hard time figuring out how to create a static library until I found Building static libraries with the iPhone SDK though I still need help in adding framework level support. Hopefuly, other people can contribute to the open source project. You can send me your suggestions and comments as well via email “bhatti AT plexobject DOT com” or tweet me at bhatti_shahzad.

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