Documentation:Turnkey session 7: Expressions

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

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Part 3 Derivation properties

clicking up the system prototyper and starting

0:00:16.580,0:00:19.680 the system connecting to our database

0:00:19.680,0:00:23.500 and here we can write expression

0:00:23.500,0:00:27.960 what happens here ia that we have a database with

0:00:27.960,0:00:31.609 objects in it and somehow we want

0:00:31.609,0:00:34.800 to transport those objects

0:00:34.800,0:00:39.649 into our application and

0:00:39.649,0:00:48.660 this is what the turnkey application does for us, we do this by

0:00:48.110,0:00:53.010 using different expressions one common operator is

0:00:53.010,0:00:56.090 all instances and all the instances

0:00:56.090,0:00:59.109 mean that it takes all of

0:00:59.109,0:01:02.320 the class referenced

0:01:02.320,0:01:05.950 and post them back to the application and I look

0:01:05.950,0:01:09.049 how that looks in the debugger

0:01:09.049,0:01:11.880 I'm gonna use the class car from our model and allinstances

0:01:11.880,0:01:22.330 we see four cars that the database, so far

0:01:24.990,0:01:30.430 and if you 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 brand.name

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