I am building a "Survey" type application. The user answers a set of questions with pre-vetted answers.
Question: Where do you live?
Answers: England, Finland, Spain, France, Monrovia
The answers in this case would be in a DropDownList.
Once the user has completed the basic responses (location, age, sex etc) I would like to be able to prevent them accessing the rest of the survey based on their answers.
So for example, if they live anywhere but England I want to direct them to a page which says "Thanks, but Monrovian's can't complete this survey". I need my filtering to be user configurable (Table based) and I need to be able to have ANDs and ORs.
So one filter being the user MUST earn 100k+ a year.
Another being they must either live in Spain, or be female AND like model trains - "100k+ && (Spain || (Female && Trains))"
I would usually use Enums and bitmasking for this, but as my country list is 200+ items long, I can't think of a sensible way to store the filtering.
Hopefully I have made some sense and someone has a decent solution :)
I don't know if I can answer your question completely, but I'll try...
So, we have a bunch of Views that are only visible to the user if she previously chose some answers, like, she will see view#3 if she is older that 30, and view#4 if she is younger than 30 AND from China, and view#5 if she is older than 40 AND from Spain OR Italy, and so on...I want also to introduce the notion of **step**, and for each step we could have 1, 2, or more corresponding views. Each view should have a set of rules (like the ones above) that define if it is displayed or not.
How to create these rules? These rules could be simple instances of a Filter class/interface that, when asked, should return true/false. Like this:
interface Filter {
boolean apply();
}
Then you can create Filters like 'older than 30', 'from Spain', whatever. Remember that each view is configured with a set of rules (Filters) so it can answer yes/no if asked if it can display itself.
Next, how to apply these filters?
We could have a controller object that only knows about **steps** (each step can have one or more corresponding views, as I said), and, after the user pressed **next** at the current step, it should collect the answers and apply them against the rules attached to each view. Like, take the answers from step one, and apply them to all views from step two, and see which one matches (returns true). For example, at step two, you can have two separate views, one for young people, other for old people, and you apply the rules from each view to decide if you show the old or young view.
I could give you one code example, and you could also do research on your own, since I know nothing about your technical environment. I have used Google Guava's predicates on a similar problem and here it is: suppose we are dealing with Witch objects, and each of them has name(string), age(int) and spells(collection) attributes. If I have a list of witches and I need to sort them based on specific criteria, I can do:
// first I want to sort witches by age(natural ordering) then by spells,
// and then by name lexicographically
Ordering.natural()
.compound(new BySpellsWitchOrdering())
.compound(new ByNameWitchOrdering())
.sortedCopy(witchList);
The above line of code is going to take the witch list and return a list of sorted witches according to the criteria. Your situation is pretty similar.
Next, how to create the answers? For each view(page), you have possible answers, like, for view#1, you can have : age, sex, race, country. You can construct some answers, in the form of strings, ints, enums, and pass them to the controller, which in turn is going to apply them to each view corresponding to the next step.
As for how to store the rules in the database, as an example, you could have a column defining rule name (like, OLDER THAN) and one column for value, say, 30. Again, I do not know that much about your environment, and it is a really general issue, so I will stop here...
Related
i want to do a autoshop software... where they keep up the cars they have and what they need(engine and other parts for example) but i dont know how to do the database to accept multiple items at once
example:
a car needs on one visit to the auto shop:
left frontal door
tires
oil change
filters
how to i add this in one go to the database(with prices included) so that i can see it all after and print a bill wheer it shows all... but my main priority is being able to insert all in one go and in one table
Hard to tell without any idea about your db strucutre. Lets assume db isn't constructed yet, you don't want to decrease parts stock or keep any track of wich exact part (i mean with serial etc.) was used. You want it quite simple, just a table with a car bought some parts.
In this case i woulde use a table looking like this : id|date|car_id|parts_used
where parts_used is a string containing parts and prices with separators. For example : "left frontal door=500+tires=100+oil=10" and then split the string when reading db.
I'm not sure it's what you want but your question isn't quite precise :)
I'm building a chatroom application, and I want to keep track of which users are currently in the chatroom. However, I can't just store this array of users (or maybe a list would be better) in a field in one of my records in the Chatroom table.
Obviously one of the SQL data types is not an array, which leads me to this issue: what is the best way to fake/mock array functionality in a SQL database?
It seems there are 3 options:
1: Store the list/array of users as a string separated by commas, and just do some parsing when I want to get it back to an array
2: Since the max amount of users is allowed to be 10, just have 10 extra fields on each Chatroom record representing the users who are currently there
3: Have a new table Userchats, which has two fields, a reference to the chatroom, and a user name
I dunno, which is the best? I'm also open to other options. I'm also using Rails, which seems irrelevant here, but may be of interest.
Option 3 is the best. This is how you do it, in a relational schema. It is also the most flexible and future-proof option.
It can grow easier in width (extra columns say, a date joined, a channel status, a timestamp last talked) and length (extra rows when you decide there now can be 15 users in a room instead of 10).
The proper way to do this is to add an extra table representing an instance of a user being in a chatroom. In most cases, this is probably what you will want to do, since it gives you more flexibility in the types of queries you can do (for instance: list all chatrooms a particular user is in, find the average number of people in each chatroom, etc.) You would just need to add a new table - something like chat_room_users, with a chat_room_id, and a user_id.
If you're deadset on not adding an extra table, then Rails (or more specifically ActiveRecord), does have some functionality to store data structures like arrays in a SQL column. Just set up your column as a string or text type in a Rails migration, and add:
serialize :users
You can then use this column as a normal Ruby array / object, and ActiveRecord will automatically serialize / deserialize this object as you work with it. Keep in mind that's there are a lot of tradeoffs with this approach - you will never be able to query what users are in a particular room using SQL and will instead need to pull all data down to Ruby before working with it.
I was reading a similar question on SO: How update an entity inside Aggregate, but I'm still not sure how a user interface should interact with entities inside an aggregate.
Let's say I have a User, with a bunch of Addresses. User is the aggregate root, while Address only exists within the aggregate.
On a web inteface, a user can edit his addresses. Basically, what happens is:
The user sees a list of addresses on its web interface
He clicks on an address, and gets redirected to this page: edit-address?user=1&address=2
On this page, he gets a form where he can modify this address.
I we decided to bypass the aggregate root, this would be straightforward:
We would directly load the Address with its Id
We would update it, then save it
Because we want to do it the DDD way, we have different solutions:
Either we ask the User to get this Address by Id:
address = user.getAddress(id);
address.setPostCode("12345");
address.setCity("New York");
em.persist(user);
The problem with this approach is, IMO, that the aggregate root still doesn't have much more control over what's done with the address. It just returns a reference to it, so that's not much different from bypassing the aggregate.
Or we tell the aggregate to update an existing address:
user.updateAddress(id, "12345", "New York");
em.persist(user);
Now the aggregate has control over what's done with this address, and can take any necessary action that goes with updating an address.
Or we treat the Address as a value object, and we don't update our Address, but rather delete it and recreate it:
user.removeAddress(id);
address = new Address();
address.setPostCode("12345");
address.setCity("New York");
user.addAddress(address);
em.persist(user);
This last solution looks elegant, but means that an Address cannot be an Entity. Then, what if it needs to be treated as an entity, for example because another business object within the aggregate has a reference to it?
I'm pretty sure I'm missing something here to correctly understand the aggregate concept and how it's used in real life examples, so please don't hesitate to give your comments!
No, you're not missing anything - in most cases the best option would be number 2 (although I'd call that method changeAddress instead of updateAdress - update seems so not-DDD) and that's regardless whether an address is an Entity or Value Object. With Ubiquitous Language you'd rather say that User changed his address, so that's exactly how you should model it - it's the changeAddress method that gets to decide whether update properties (if Address is an Entity) or assign completely new object (when it's VO).
The following sample code assumes the most common scenario - Address as VO:
public void ChangeAddress(AddressParams addressParams)
{
// here we might include some validation
address = new Address(addressParams);
// here we might include additional actions related with changing address
// for example marking user as required to confirm address before
// next billing
}
What is important in this sample, is that once Address is created, it is considered valid - there can be no invalid Address object in your aggregate. Bare in mind however, that whether you should follow this sample or not depends on your actual domain - there's no one path to follow. This one is the most common one though.
And yes, you should always perform operations on your entities by traversing through aggregate root - the reason for this was given in many answers on SO (for example in this Basic Aggregate Question).
Whether something is an entity or VO depends on the requirements and your domain. Most of the time address is just a Value Object, because there's no difference between two addresses with the same values and addresses tend to not change during their lifetime. But again, that's most of the time and depends on domain you're modeling.
Another example - for most of the domains a Money would be a Value Object - 10$ is 10$, it has no identity besides amount. However if you'd model a domain that deals with money on a level of bills, each bill would have its own identity (expressed with a unique number of some sort) thus it would be an Entity.
I am not sure what SQL is exactly, databases I think, would SQL be the thing to use?
I want it so that when a user types into a search box it displays a "did-you-mean" box, that also shows how many other people used that term but I will do later ;)
currently I just want the text to be saved into database (?) and also how many times it's been done.
(new to stackoverflow so sorry if format/whatever is bad)
You just need a three table named something like search_queries which has columns for: id, search_text, and count. Everytime somebody searches just increment the count column where search_text is equal to what they searched for. This is a really broad question though and you need to start by learning the basics and report back here with more specific questions.
I have a problem naming the elements in my application's data model.
In the application, the user has the possibility to create his own metamodel. He does so by creating entity types and a type defines which properties an entity has. However, there are three kinds of entity types:
There is always exactly one instance of the type.
For instance, I want to model the company I am working for. It has a name, a share price and a number of employees. These values change over time, but there is always exactly one company.
There are different instances of the type, each is unique.
Example: Cities. A city has a name and a population count, there are different cities and each city exists exactly once.
Each instance of the type defines multiple entities.
Example: Cars. A car has a color and a manufacturer. But there is not only one red mercedes. And even though they are similar, red mercedes #1 is different from red mercedes #2.
So lets say you are a user of this tool and you understood the concept of these three flavors. You want to create a new entity type and are prompted to choose between option 1, 2 and 3. How would you name these options?
Edit:
Documentation and help is available to the user. Also the user can be expecteted to have a technical/programming background, so understanding these three concepts should be no problem.
First of all let me make sure I understand the problem,
Here's what you have (correct me if I'm wrong):
#of instances , is/are Unique
(1,true)
(n,true)
(n,false)
If so,
for #of instances I would use single \ plural
for is\are unique (\ not unique) I would use unique \ ununique.
so you'll get:
singleUnique
pluralUnique
pluralUnunique
That's the best I could think of.. I don't know exactly who are your users and what is the environment, But if you have an option of adding tips (or documentation) that should be used for sure.