MDrivenWiki
Log in

Difference between revisions of "Turnkey session 7: Expressions"

From MDrivenWiki
Line 82: Line 82:
 
== OCL expressions ==
 
== OCL expressions ==
  
       To learn more about the object constraints language you can watch the OCL Sessions Series
+
       To learn more about object constraint language expressions (OCL expressions) you can watch the OCL Sessions Series
  
 
[[Part 1|Part 1 OCL Common Expressions]]
 
[[Part 1|Part 1 OCL Common Expressions]]
 
 
[[Part 2 OCL: Derivation. Associations|Part 2 OCL: Operators]]
 
[[Part 2 OCL: Derivation. Associations|Part 2 OCL: Operators]]
 
[[Part 3 OCL: Derivation properties|Part 3 Derivation properties]]
 
[[Part 3 OCL: Derivation properties|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
+
We can use the system protoyper to connect to our database and write expressions. There are objects in the database that we need to transport into our application. And this is exactly what the turnkey application does by using different expressions.  
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
+
One common operator is '''all instances'''.  It takes all of the class referenced and post them back to the application. Following the explanation in the video if we have a set of objects, we have different types of operators - likes size, for example,it would return 6, but in our case we have 4 cars.
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
+
So we can stack the operators after each other and use all instances to make size returns 4.
different types of operators
+
There are many different operators look at '''"last"'''.
 
+
It checks the list of retrieved or selected objects and  picks the last one. There's an operator called '''"first"''' - that does almost the same thing, but with the first one.
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
+
'''Order by''' is an operator that could sort our objects on some property. Let's say that is  B C A D E F "oreder by" on that property would fetch "A" first "B" then "C" "D" "E" "F".
and we could combine, so that's
+
'''SubSequence''' operator  takes only a subset of returned set from allinstances. For example 1,2, like that, so instead of 4 we have got only two and we could combine, so that's
  
 
0:04:26.310,0:04:33.710
 
0:04:26.310,0:04:33.710

Revision as of 12:56, 22 January 2017

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.

To make your experience more comfortable, we set the main tags mentioned in the video to the right bar menu of this mini player. Choose the interesting subtitle on the list and immediately get to the exact theme timeplace in the video. Now you can pick any topic to be instructed without watching the whole video.

"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 object constraint language expressions (OCL expressions) you can watch the OCL Sessions Series

Part 1 OCL Common Expressions Part 2 OCL: Operators Part 3 Derivation properties

We can use the system protoyper to connect to our database and write expressions. There are objects in the database that we need to transport into our application. And this is exactly 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. Following the explanation in the video if we have a set of objects, we have different types of operators - likes size, for example,it would return 6, but in our case we have 4 cars. So we can stack the operators after each other and use all instances to make size returns 4. There are many different operators look at "last". It checks the list of retrieved or selected objects and picks the last one. There's an operator called "first" - that does almost the same thing, but with the first one.


Order by is an operator that could sort our objects on some property. Let's say that is B C A D E F "oreder by" on that property would fetch "A" first "B" then "C" "D" "E" "F". SubSequence operator takes only a subset of returned set from allinstances. For example 1,2, like that, so instead of 4 we have got only two 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