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Turnkey session 7: Expressions

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Session 7 - In this session we take a deeper look at OCL expressions and what you can do with them. OCL is a complete language that can act on everything that you have in your model, it has operators on objects and on collections. The ocl language is a functional language –different in approach compared to imperative languages like javascript and c#. The ocl language is optimized for querying your model. It uses a bit of set theory from your math classes. It is compact in the sense that it does a lot with short snippets. OCL is defined by ObjectManagementGroup OMG.

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"all instances" expression "Last" expression "First" "Order By" SubSequence Combine the expressions select operator combine with logic expressions loop variable

OCL expressions

     To learn more about the object constraints language you can watch the OCL Sessions Series

Part 1 OCL Common Expressions

Part 2 OCL: Operators

Part 3 Derivation properties

 Starting from clicking up the system prototyper and starting the system connecting to our database and here we can write expressions. What happens here is that we have a

database with objects in it and we want to transport them into our application. This is what the turnkey application does by using different expressions. One common operator is all instances. It takes all of the class referenced and post them back to the application. And if we have a set of objects, we have different types of operators

0:01:30.430,0:01:33.610 likes size, this one operator in this case it would

0:01:33.610,0:01:38.320 return 6, but in our case we have four cars

0:01:38.320,0:01:42.720 I look on how that looks

0:01:42.720,0:01:46.540 so we can stack the operators after each other like now we use

0:01:46.540,0:01:50.940 all instances and than size it returns four

0:01:50.940,0:01:54.080 yeah, many different operators

0:01:54.080,0:01:57.790 look at last

0:01:57.790,0:02:01.090 it checks the list of retrieved

0:02:01.090,0:02:05.490 or selected objects and picks the last one

0:02:05.490,0:02:10.260 returns only one, there's an operator called first

0:02:10.260,0:02:13.550 that does almost the same thing but

0:02:13.550,0:02:16.709 the first one, so let's check

0:02:16.709,0:02:23.209 that in the debugger as well

0:02:30.069,0:02:34.760 25, and now we take the first the one with tire radius 5

0:02:34.760,0:02:38.750 order by

0:02:38.750,0:02:42.099 is an operator that could sort

0:02:42.099,0:02:45.980 our objects on some property

0:02:45.980,0:02:49.390 so let's say that is

0:02:49.390,0:02:53.590 B C A D E F

0:02:53.590,0:02:57.260 oreder by on that property would fetch "A" first

0:02:57.260,0:03:03.260 "B" then "C" "D" "E" "F"

0:03:03.409,0:03:09.000 we can try that in the debugger as well

0:03:15.240,0:03:17.810 order by

0:03:17.810,0:03:21.960 changes to registration number

0:03:26.080,0:03:29.980 now they are sorted by registration number

0:03:35.350,0:03:37.780 SubSequence

0:03:37.780,0:03:41.110 spell that wrong it's "q"

0:03:41.110,0:03:46.820 not "c"

0:03:48.920,0:03:53.140 takes only a subset of returned set from allinstances

0:04:06.510,0:04:10.810 1,2, like that, so instead of 4 we have got only two

0:04:16.739,0:04:20.130 and we could combine, so that's

0:04:26.310,0:04:33.710 add the order by registration number that we had before behind here

0:04:33.180,0:04:39.810 then we get one set and if we would move the order by

0:04:39.810,0:04:43.130 in front the subsequence we get another result

0:04:43.130,0:04:48.860 the most important operator

0:04:48.860,0:04:54.010 that you will use most likely is 'select' it requires some boolean value

0:04:54.010,0:04:57.250 so it checks each and every

0:04:57.250,0:05:00.800 value object that runs through on some property

0:05:00.800,0:05:04.979 checks if it has it and then it either

0:05:04.979,0:05:09.169 chooses to return it or not

0:05:09.169,0:05:12.669 let's now select on tire radius

0:05:19.330,0:05:24.470 in this case a radius bigger than 5 returns 2 objects

0:05:24.470,0:05:26.530 bigger or equal 5

0:05:26.530,0:05:30.470 it returns three objects

0:05:30.470,0:05:35.620 that's okay, when it comes to select you can

0:05:35.620,0:05:38.990 combine any boolean expression like logic operators with 'and'

0:05:42.080,0:05:47.220 and 'or' 'not' and things like that

0:05:47.220,0:05:51.060 so let's add another constraint here to

0:05:51.060,0:05:56.909 should be Volvo, then we get two

0:06:02.330,0:06:07.319 and one important concept in using select

0:06:07.319,0:06:10.659 is the loop variable

0:06:10.659,0:06:14.009 the loop variable is the name on the

0:06:14.009,0:06:17.139 iterated object it's in the expressions

0:06:17.139,0:06:20.650 gonna call that "one car" then there's a pipe sign

0:06:20.650,0:06:24.710 so means that we could use

0:06:24.710,0:06:27.919 this variable "one car"

0:06:27.919,0:06:31.270 in our expressions it helps when

0:06:31.270,0:06:34.830 the expressions get complex and change

0:06:34.830,0:06:39.190 the volvo brand to audi and see how that works

0:06:39.190,0:06:42.650 okay that was a few things on expressions

0:06:42.650,0:06:45.000 subscribe to this, thank yous