Part 5 Searching in databases
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Hi and welcome back to MDriven designer overview
and this will be session five, so we
ended off the last session with the
creating a modal dialog that were
allowed us to pick tenants to our house
so we could pick persons that would
create lease contract and when we used
this dialogue "all persons" to to pick
the tenants from and as you can
imagine this strategy simply will not
hold, if we have a million persons and
this is good, when we have a hundred
maybe, but we can't really trust on all
instances to come to the rescue for
every scenario, we really desperately
need some way to vSeek the database
without instanciating the objects in
memory in their client during the
prototyper, so how do we go about that in
the view model pattern that we have
we don't like this, we right click and among the nesting
choices we have add add search expression
and such expressions are expression step
are supposed to be executed in
persistent storage, so that will be a
database if your back and is connected
to it, to one or it will be the xml file
in our case, where we prototype against
the xml file and if we are in turn
key will be the persistence mapper that
in turn will question the backing database
alright, so let's just go ahead and add
a search expression or maybe better
yet, we will do a new view model to keep
the searching and we will column this
"person search" and we type it to be "person"
right click and in the nested view models
add search expression and what happened
here, was that three columns were
added to the root and one of the
columns was a variable called the
vSeek result, this variable was created
and added to the viewmodel well it
wasn't because it's implicit, but it
should be in the newer versions, it will
be and so variables are just as they sound
something that we can define in
the view model and is only available
in the viewmodel scope, so this one
should be of collection person this is
where our result is going to end up from
a search and that one we connect to a
search result grid, so we have another
variable vSeekParam that is
defined as a string, so we have a column
in the UI that lets the user enter
a criteria and we have his search button
and the search button as the ocl
expression "selfvm.search", "selfvm" is
a special instance that is available in
view models only from OCL, let's see
what it contains, "selfvm." and from
here we can do things as
refresh, save, search, and a few other
things, like PSexpression_refresh, we can
come back to these in later sessions, but
for now we just going to use the vm
search, what the search operator does is
it looks for search expressions in the
view model and this is a search
expression, it's just another view model
nesting, but what separates this from the
other nestings is that it is not
connected to anything it's judt sits here
in the middle, doesn't need to be in the
middle because I said so I can right
click this and move this one up, so as
such expression is typed and it has
criterias right here it's just columns you
can have many criteria per search expression
the criterias are merged
together with the ocl operator
intersection, so what if these criteria
is true and we had another or this
criteria returned five persons 12345 and
we had another one that return two
persons 45, the intersection will take
what's equal between the two domains
so 4 and 5, but the search expression
the criteria is just another ocl, but
what's different about this is that is
the persistent storage subset of SQL Ocl-PS
it sets up here in the edge
when we entry and then we don't have access to every single
operator, we can't concatenate
strings etc. in this language
its main purpose is to be easily
transformed to SQL and executed as an
SQL query to the database and the
database will return a number of
identities, that we will in turn
interpret as persons and load personal
objects, so what we do is select and we
have a loop variable called A then
the mechanism to create the search
expression and all this for us it just
took the first string attribute of the
class that we had set person and that
was first name and set, well it's not
unlikely that is what you as a
developer want to limit search of,
this attribute as SqlLike(vSeekParam) and ends with a +% just like in
Sql operator like, so if you want to find
both and start, if you want to find
values that equals in the middle
that you would go something like this,
so this will be a resulting string that's
add into the SqlLike, that of course
will be translated into a like operator
in sequel, but as we are running against
an xml file, it will do something similar
just execute operator on that
so is this really what we want
well, we want to also check if it's the
last name maybe, so I use "or" and I use "LastName", like that
what should I show for a result I can show the things I have
first name and last name
so let's do one thing more in this view
and if you don't find what you expect
you might want to have somewhere where
you can create a new person, so let's
totally action definitions for this
dialogue and let's do a viewmodel action
and say that we should show it on the
root and say new person and the
execute expression on this one
should be PersonCreate, having done that
we can see, if we have, we can save this
push the play button, start system, Run Model
and continue, we never created an
action to actually show the seeker
view model, so person search
I right click on this and say add a
global action for show
okay then it's shown here, but we
probably want to sort into as menu group
a double click it
find it here set menu group-seekers
maybe, so this is might be where I want
to put all my search dialogues and who
knows
having done that and I head back to this one
model refresh, seekers, show per person,
search and I can search, but I only want those
that has an "a" in them
that's the only one, okay but
what if someone's missing
I can create a new person and call that
Andersson Anders, now if I search for a
I should find Anderson, but since
my xml file is, I guess it is case sensitive
it is case sensitive, so if we don't
like that we should have used operator
called .sqlLikeCaseInSensitive, where like
so now we have the searcher
let's go back to the house view
where we added the pic tenants action
so the pick tenant action and let's do
a copy of this, where did he go
let's do a copy of this, just going to do
a copy and paste, and "pick tenants by search"
and that one should bring up the
person search instead and if it does
it cannot call "check this" because that
variable doesn't exist in that UI like
instead it calls "SearchResultGrid" if that is empty
ok and this expression won't go either
because the same problem, like that
and it adds the tenants if I have selected any
so if we head back here we see that we have
another action pick tenants by search
of course in the end, I only want one of these
and our most likely it's the "BySearch"
that will survive and then maybe
I will change its name, model refresh,
houses and pick one here,
this doesn't have any tenants, I'm going to pick
tenants by search, I'm going to search on
find this one and I add that one, so I find it
rather disturbing that I don't see the name here
this is what I talked about
before, in session 2 or something
first, when we do the UI
and watch the information together
that it's obvious that, of course, we need to see
the name here as a new requirement, but
it's obvious now that we see the result and that's not a problem
this is the grid, which is this one, which
points to this one and let's add the columns
and add a generic column and in
that generic column sets an expression
that follow the role to tenant and the
first name that's the ocl editor acting up
when you don't have a separator
first name and you might have noticed that
I quite a lot of times had a need
to concatenate first and the last name
because that's simply how we
refer to persons, so this
sort of this pattern comes back
again and again and we're going to solve
this in just a minute, just going to save
the fact that we did a new column
and we call that "tenant name" and
we might want to give that a little more
space like three columns and we might
want to drag this one to the end
here and over there, and this one and we
added in summary session it's just we want
so if I save and refresh and look at all
the houses, was it this one and there's
Andersson, but I don't want it there
I want it first and let's show the
gridlines, like that, refresh like
that and that's pretty obvious and
how come this isn't even showing, well
it's too tight to show with this
style, so how would you solve that
well as you can see we are cramming
everything into one grid cell here
so we're gonna insert column and
give this one more space for the presentation
let's give it 2 and just to make things
look straight you're going to get the
rest of them 2 as well, head back,
refresh, views, all houses, when I click it
would still crap but you get the
general idea I will just insert yet another column
let's judt do that one for and refresh, like that
so this is important how quickly
we can go from feedback with our eyes
that this isn't good back to design how should be instead
back to verification, okay it's fine it
really saves everyboy's time
ok enough about that, and I said that
this pattern is repeated again and again
yes it is the first name and last name
it's a really common scenario that we
want to refer to persons by their full
name, so what we probably would want
to do is add an attribute, that is called
full name, but that wouldn't be very
normalized to store the first name and
the last name and full name, so let's
make that one right, that's another
attribute mode, it's not persistent as it
is not stored in the database, it's
derived as it's calculated from other
values that we do have, so I can paste in
that one and now that was for the
tenants and I don't want that
because now we are in the scope of a person,
so first name and last name
this makes up the full name and now we
have done this and we can make use of it
in our view models or wherever we access
model information, so instead of doing
this we can just as well do the full
name, like that and now it's grey I was
expecting it to be pink, because it is
derived I wonder why that was it's derived
don't have an answer, but going to save
what do you say? self is not...
that was just wrong, save and head back and
model refresh, and there's really
no difference, but like here now that we have it
let's use it, so tenance last name
and tenance full name is full name we got refresh
if I were to change the name
the right attributes were like this
there are always subscribed, so let's head
back to this view and add it as well
just to prove a point all persons add column
full name,  give it some space when it's in grid too
maybe we refresh, views, show all persons
as soon as I change one of their values
that build up the derivation, the
derivation will kick in and invalidate
as the UI looks at this value
it will force it to refresh, getting the
parts of the value and re-evaluate it,
so when I write Hans it will be updated
and if I were to change anything
it will be updated and that might be
Dick Smith, right, so derivation is also
available for associations
so what we could do, if we want to know
where the person lives is of course to
follow to see the rented apart and
look up the street for that house
but if that is a common operation
that we want to do we could
also add a association straight from
person to streets and since
I can rent many apartments, I potentially
have many addresses, so if I want to
derive this from available information,
I was saying that the association is derived
and I will take this end, will
have no value so I will say that there
it is non navigable, is navigable
false, because if I would want to go from
street to persons that would be another
derivations that would have another
expression, but this one should have
a derivation expression, that it starts
in person and it goes to
here is the one that is derived it
goes to owned house,
no, to lease contract, and from lease contract
rented apartments, and from rented
apartments - the street
I really must fix that, the street
so this will be a collection of
streets and if we were to show this in
our UI, I guess we could add column and
add generic column, and I follow the
relation to streets and that has a name,
but since this is a collection of
strings, we need some way to display it
in a single cell that we will do here in
the grid and done an operator that's
real handy for these cases as CommaList
so it will take all the strings in
the collection and append them as they
with the comma in between, so lives at, so heading
back to refresh, views or persons, so
here we see the address is swelling
ok, so good we have covered in a lot of
ground we have mentioned derivations
for attributes like the full night
servations for associations like the
street even if it was kind of silly,
because we would probably would like
the street number to get the precise
address and that's not possible this way
we have covered the idea of being able
to vSeek in a lost database and then
we also mentioned variables that are
available in view models, so I'm going to
show you another thing and what if we
are in a situation where we actually
need some test data, we need a lot of
persons to verify that our idea to search in
larger amount is valid and of course
we could run the prototype print
and press, we added the new person action
here and we could press that a thousand
times to enter the first and last name
but is there a better way, you ask
and since I talking about it you have
probably guessed that there is and I go
into the the Run button again because
I need a context that we are in the
XML persistence, we're going to start
the system and we're going to go into
the legacy debugger and in here we have
a tab over here
"import tab separated", so tab separated
data import via named view model, so what it
says he's given tab-separated data and
the view model name assumes row 1 in data
to be viewmodel column and creates
instances of view model class
so basically, if we have some data that
we paste in here, we should be able to
create objects of certain class, but it
also says, that we need a view model,
so let's create one, as you see the view
models are used over and over for different purposes
ImportPersons and type Person and let's assume
the first name is the first value and
the last name is the second value so
that's about it and given that I should be able to say
that this is the view model I want to
use or maybe I need to reread this, I do
start, lazy debugger,
input tap separated and view model and
get header from view model,and first-name
lastname alright, where can I get that, I found this site
as google for a list of names and find
anything on google list of random names
let's do 50 and male and female and well
no alliteration when you start the same ok
now I want to grab these on listing text
area, that's great, I wonder if this is
tab separate it probably isn't and going to
start notepad, alright so is that a tab
no, I copy tab and I want to
do is search and replace here, look
for space and paste in my tab and
replace it all and copy those and head
back to my importer and paste those, and
go, so that means I got a lot of dirty
objects here that I will save like that and
head back to my this one is going to
restart, person search and I have some
test data to work on
oh let's see everyone that starts either
their first loss name with "t" or has a "t"
really because that was what we said in the criteria
ok, so that means that when we do houses
and we want to assign tenance by search
and we do everyone with the "T"
because it is case sensitive as we
found out and select them and press ok
then we have those as tenants
alright moving ON as we see the
tenants here, but they haven't got
an apartment number...they
haven't got a rent figure, but they
really should this is important information
it's so important, that we might want to
add constraint on our class lease
contract to make sure that
the user of the system is made aware of
the importance of these values
so I select the class and I select
constraints and I get a little dialogue
where I can add constraints this
constraint I give a name "must have
apartment number" that's the name of my
constraint so that I can refer to it and
and I want to have a description as well
and I'm going to make easy to myself is
to do something like this, that's right
the expression is more or
less self.apartmentnumber and well it
should be not null, right
shouldn't be null and then now we got
that symbol that says that this has one
constraint, so when we look at our
diagrams we will see that this is
constrained in some way
ok, so if we were to head back to our
prototyper and show the house
we see, must have apartment number
must have apartment number, but there's
really no information on who is missing
the apartment number and let's head back
to the constraint and in the description we can actually
access attributes, so and we can
go like this as string within the
larger than and smaller than, greater than and
tags to say that we want to describe
the default presentation here, can you
please inject that and what is the
default presentation, default string
representation on lease contract is none
okay, but we might follow the link to the
person and use the full name again we
made use of the derived full name
like that and save, and head back, refresh, view
all houses, so Hans Karlsen must have an
apartment number and Dick Smith must
have apartment number and as I give our
Hans Karlsen apartment number one
that is removed and as I give  Dick's one 2
that one removed as well, so that's a
good way to feedback information to the
user about what needs to be filled in
but it might not be enough for us, we
might need to stress these even harder depending on use case
so there's more ways to signal the
user that something needs to be done
if we check the house view here and we had
the variables that we don't use in this
view we use them in the seeker, but we
also have the the constraints, so these
are the constraints that we found in the
classes that are used here that is just
one and depending on use case we might
not want to show it because who knows
the view might not even contain
their apartment number, so no need to
stress the user about entering it if it
isn't really possible, so that we could
just opt it out, but we want to have it
opt-in because it's good for us, but what
we could do is something more precise as a validation rule
let's right-click up in the top and add
a validation rule, so we got rule one and
then the rule one is that
let's say it's the fact that the selected, what
what I want to do is to highlight something here
apartment number to make the user see this
so what is this, this is here
the lease contract, so what I want to do in
my validation rule is to find a
variable the current
the lease contract and check that one
that particular one that sunscreen and
or selected at the moment, and check that
for apartment number and verify that
isn't null, and then I can write something
please supply number
like that, but we still haven't been able
to say that this rule
is supposed to show up for this field
that I can select the field it's over
here and I'm supposed to find it and
validation rules, my menus really turn
out the wrong end all the time,
validation rules, rule one, please supply number
ok, so that would be one way to
further gearsteer our user to see
something, but how does it look
refresh, view, houses
it doesn't show anything, but if I null
that out first I get this one and I also
get the red information here
actually depending on what style you use
it really renders differently, so that
you can control
this and we have examples, where you just
have an "!" that was when you point that
it states what's wrong with it
so this is another important thing I
should mention that,when you have errors
and there's some something and updated
in  the information and you try to
save then it will ask you, there are
errors in the information, do you really
want to save anyway? "Hans Karlsen must
have apartment number" and the system
won't stop you from saving and this is
an important principle I think, that you
shouldn't stop the user from entering
information, even if it isn't correct
then it's better to to monitor all the
information that is in incorrect, so that
they can come back to it then and update
it don't stop users from entering data
and make a UI very clear, what you expect
but you should always
always honor the users' request to
save and maybe you should work with
the quality attributes like states that
you can't go into approved, before you
have apartment number or the rent in
dollars, but you shouldn't stop them from saving
ok, that's just my very clear view on this
ok, so I'm going to save it anyway, but run
nice wouldn't you say
just having the area information this
way, so whenever I enter something the
error goes away and of course I don't
get the warning, when I save, but that was
not a very good side for this example, so
switch back, so let's add
another constraint and we make that
not to error constraint, but rather look at
the other types of constraints, so we
have a constraint the "rent" and
the description and we do as we before "<as
string> lives free" and
we don't do an error just the information
expression would be self.rent->not null
because when the expression
is true then the constraint is
fulfilled and we don't shoe anything, but
as soon as the constraint is not true
then it's broken and then we show warning signs etc.
in this case information
refresh and now it's a little white
thing is Hans Karlsen lives free
shouldn't be the case that let them say alright
I wonder if we will have time to
cramming reports in this, so that we
could do rents and rents slips for these guys
I think maybe we'll come back to
that in the next session so we will
round this off and thank you very much
for following along with these tutorials and I'll be back

Revision as of 21:56, 15 April 2017

We create a seeker that translates ocl to sql for searching in databases of any size. We look at derivations, constraints and validation rules.

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View Model Editor: Search expressions Variables and Validations Derivation Attribute Visible expressions Test data: Tab separated data import Constraints Validation Rules Saving despite error warnings

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