OCL aliases

-
This is just a copy/paste of a reply I made in a newsgroup, but I think it is quite informative so here it is....

KEY
Square brackets denote a class [Person]
Rounded brackets denote a role (Pets)

Let's say you have a Car class and a Garage class, an individual car is regularly serviced at a specific garage so you have the following association

[Garage] (Garage) 1----0..* (ServicableCars) [Car]

  Car.allInstances->select(Garage.Code = '1234')
The above OCL will fail because "Garage" is a class so the parser is expecting stuff like "allInstances". So you might think this should work

  Car.allInstances->select(self.Garage.Code = '1234')
but it doesn't because "self" refers to the root object and not the object at the parsed node where it is specified. This is what aliases are for:

  {aliasname} + {pipe}

  Car.allInstances->select(currentCar | currentCar.Garage.Code = '1234')
This was possible in Bold too (native windows predecessor to ECO), but in Bold you could differentiate between members and classes through case sensitivity. PascalCase always meant a class whereas camelCase always meant a member, so this would work in Bold but doesn't in ECO as it is not case sensitive

  Car.allInstances->select(garage.code = '1234')
Although ECO is not case sensitive you will notice that I still use the
sensitive format for clarity :-)

Comments

Post a Comment

Popular posts from this blog

Connascence

-
I’ve just finished reading What every programmer should know about object oriented design . The first couple of sections are a bit useless really, but the 3rd section is very good. I particularly liked the section on the difference types of connascence in software. There’s some basic information about it here if you fancy a brief overview of what it is about. It’s a really good book, I recommend you read it! Should only take a day if you only read the 3rd section.
Read more

Convert absolute path to relative path

-
Today I needed to convert an absolute path to a relative path based on a specified base path. E.g. c:\a\b\c -> c:\a\b\c\d\file.txt = d\file.txt c:\a\b\c -> c:\a\file.txt = ..\..\file.txt c:\a\b\c -> c:\a\x\file.txt = ..\..\x\file.txt I am surprised there is nothing in the .NET framework so I had a hunt around and converted the code from the following URL ( http://www.vergentsoftware.com/blogs/ckinsman/default.aspx?date=2006-08-07 ) into C#.... private string RelativePath(string absolutePath, string relativeTo) { string[] absoluteDirectories = absolutePath.Split('\\'); string[] relativeDirectories = relativeTo.Split('\\'); //Get the shortest of the two paths int length = absoluteDirectories.Length //Use to determine where in the loop we exited int lastCommonRoot = -1; int index; //Find common root for (index = 0; index if (...
Read more

Printing bitmaps using CPCL

-
I've had no end of grief trying to print a PCX to a Zebra Printer using the CPCL printer language. Silly me, didn't notice the EG command (expanded graphics) so there was no need to convert my BMP to a PCX and then struggle with binary data. I still had a bit of grief working out how to print using the EG command because the documentation is quite frankly crap. The expected command format is EG {WidthInBytes} {HeightInPixels} {XPos} {YPos} {Data}\r\n The printer expects a 1 bit pixel matrix. So if pixel(0, 0) is set you will set "80" in the data. If pixel(0, 0) is set and pixel (7, 0) is also set you would sent "81". Basically what you need to do is to read each set of 8 horizontal pixels and then use bit operations to create a byte value 0..255, and then output this as hex 00..FF. Here's the routine :-) public void DrawBitmap(Bitmap bmp, int xPosition, int yPosition) { if (bmp == null) throw new ArgumentNullException("bmp"); ...
Read more