These day I work with a database that have this style of relationship then I've been very confused with it. This database is in a very large web app & have worked well for 10 years then I wonder whether this design is good in someway? or in which situations I should implement it?
Welcome any idea!
There is nothing wrong in my opinion. You can have, for example, in a personal_data table a place_of_birth field and a place_of_living field both referring to a cities table. By the way you should post a more meaningful example to have a more precise answer.
Related
Some of the Users in my database will also be Practitioners.
This could be represented by either:
an is_practitioner flag in the User table
a separate Practitioner table with a user_id column
It isn't clear to me which approach is better.
Advantages of flag:
fewer tables
only one id per user (hence no possibility of confusion, and also no confusion in which id to use in other tables)
flexibility (I don't have to decide whether fields are Practitioner-only or not)
possible speed advantage for finding User-level information for a practitioner (e.g. e-mail address)
Advantages of new table:
no nulls in the User table
clearer as to what information pertains to practitioners only
speed advantage for finding practitioners
In my case specifically, at the moment, practitioner-related information is generally one-to-many (such as the locations they can work in, or the shifts they can work, etc). I would not be at all surprised if it turns I need to store simple attributes for practitioners (i.e., one-to-one).
Questions
Are there any other considerations?
Is either approach superior?
You might want to consider the fact that, someone who is a practitioner today, is something else tomorrow. (And, by that I don't mean, not being a practitioner). Say, a consultant, an author or whatever are the variants in your subject domain, and you might want to keep track of his latest status in the Users table. So it might make sense to have a ProfType field, (Type of Professional practice) or equivalent. This way, you have all the advantages of having a flag, you could keep it as a string field and leave it as a blank string, or fill it with other Prof.Type codes as your requirements grow.
You mention, having a new table, has the advantage for finding practitioners. No, you are better off with a WHERE clause on the users table for that.
Your last paragraph(one-to-many), however, may tilt the whole choice in favour of a separate table. You might also want to consider, likely number of records, likely growth, criticality of complicated queries etc.
I tried to draw two scenarios, with some notes inside the image. It's really only a draft just to help you to "see" the various entities. May be you already done something like it: in this case do not consider my answer please. As Whirl stated in his last paragraph, you should consider other things too.
Personally I would go for a separate table - as long as you can already identify some extra data that make sense only for a Practitioner (e.g.: full professional title, University, Hospital or any other Entity the Practitioner is associated with).
So in case in the future you discover more data that make sense only for the Practitioner and/or identify another distinct "subtype" of User (e.g. Intern) you can just add fields to the Practitioner subtable, or a new Table for the Intern.
It might be advantageous to use a User Type field as suggested by #Whirl Mind above.
I think that this is just one example of having to identify different type of Objects in your DB, and for that I refer to one of my previous answers here: Designing SQL database to represent OO class hierarchy
I just wanted to validate my data structure.
It seems a bit convoluted to me, maybe it can be simplified?
Questions are grouped into chapters.
For each question, only one answer per session is possible.
The purpose is to be able to compare / analyze answers to the same questions (by different users or by the same users at different times, i.e. with different sessions).
A template, being a collection of chapters & questions, should not have to be replicated, if chapters and questions are the same.
(That would be necessary if Answer did not have a relationship to Session.)
Is the relationship from Answer back to Session the right strategy?
What else would you improve to simplify the model?
Thank you!
EDIT
Follow-up clarification:
The Answer is not static (e.g. "right" answer, "solution"), but some text the user inputs. It is more like a "questionnaire" than a "quiz". The answer has quantitative attributes that can be analyzed.
As stated, one question can have only one answer within a session. Because questions can indirectly belong to more than one session (via (NSSet*) question.chapter.template.sessions), they could have more than one answers and thus need a to-many relationship.
The typical scenario: User starts a new session with a certain template and fills out the answers. Then he can look at the analysis of the results and compare those with the results of other sessions that use the same template.
EDIT 2
The snapshot of the data model including attributes
honestly, this is what I would do instead of your structure, but I don't know what the purpose of the each entity because I'm not able to find out from their simple names.
this is just an idea to resolve the loop.
you can still reach all templates and all answers from the session, not directly but it does not make your life much harder.
UPDATE:
at the first and second sight, for me, it seems the Session entity is just an extra entity only here. honestly you would not need it, if you concatenate with the Template (aka Questionnaire) entity.
you have to add a many-to-many relationship between the Template and User (you can do it, don't worry about it). using this way, from each template you can reach all answers as well, and you won't have any loop.
Despite the really helpful effort by the part of #holex - the best way still seems to be to stick with my design. The simplifications I had hoped for have not materialized.
I like knockoutjs, the sooner we get rid of coding directly toward the DOM the better. I'm having trouble understanding how I would do something which I'm going to explain in terms of a question/answer site. (This is probably a general MVC/MVVM question)
In my data model I have a question[id, description] and answer[id, question_id, text]. The browser requests a list of questions which is bound to a tbody, one column will display the question description, while the other should be bound to an answer textbox.
One obvious way of doing this is to have a QuestionAnswer[question_id, answer_id, question_descrition, answer_text] model. Ideally I'd like to keep them separate to minimize transformation when sending/receiving/storing, if there isn't some way of keeping them separate then I have the following question:
Where is the ideal place to create the QuestionAnswer model ? My bet is that by convention its created on the server.
If there is such an example somewhere please point me to it, otherwise I think it would make a good example.
Please help me wrap my head around this, Thanks!
What you could do is to create the combined model on the server, serialize it to json and then use the mapping plugin to add the serialized list to the view model.
I'm doing that here only it isn't a combined model, but shouldn't make any difference. Especially since it seems like your relation is one-to-one.
If you need to create an "object" in your view model, you can use the mapping definition to do so, like I do here.
I use C# to build my model on the server, but I guess you can use whatever you are comfortable with.
The cool thing with the mapping plugin is that it adds the data to the view model so that you can focus on behaviour.
Ok,
I'v gathered my thoughts on what my question is actually asking.
To do data binding on the client side you obviously need your data model there as well. I was conflicted on what I needed to send over and at what time.
To continue with the Question/Answer site idea: Sending down a list of answers each of which have a question in them is what should be done. That way you can bind to the answer list and simply bind the question description of each answer to the first table column.
If later I want to make a question editor I would potentially send a complete different data structure down and not reuse the Answer has a Question structure previously used.
I thought there might be a way of sending down a more complex data structure that references itself. Which apparently is possible in JSon with some extra libraries.
Hi I'm new to mongoDB and Mongoid and am little bit confused on when to use embedded documents and how deep to embedd.
So a fictional example:
Library collection has_many :books, which embeds_many :pages, which embeds_many :sections
Since I cannot work with say a Section directly I have to go trough books.pages.sections, right?
This would result in this route, libraries/:id/books/:id/pages/:id/sections/:id
Which seems a little bit crazy, best practice would be to only nest one level deep, right?
One way would be to have the route pages/:id/sections/:id and then stick the bookid in the request?
Would it be harder to query on say, sections? For example if I need to find all the books where sections has tag x?
However if I don't embedd all the way I would have an extra query?
Can someone shed some light? Thanks.
First of I believe that no one can give you the right answer about how deeply you should embed documents. It is highly dependent on your concrete project requirements. In general you should answer some questions to choose appropriate schema design:
Will users concurrently update same object in collection? (or what would my boss say if clients lost their updates)
Do I need support atomic operations?
Do I need to independently show nested collections or are they queried with the parent?
Do I need to sort embedded objects?
Do I need to query on embedded objects?
If you will answer 1,2-true; 3 I need show them independently (different page); 4,5 - true then i am sure that embedding will be some kind of pain in your ass.
Extra queries should not be a problem I guess.
Good day!
I am a newbie on creating database... I need to create a db for my recruitment web application.
My database schema is as follows:
NOTE: I included the applicant_id on other tables... e.g. exam, interview, exam type.
Am i violating any normalization rule? If i do, what do you recommend to improve my design? Thank you
Overall looks good. A few minor points to consider:
Interviewer is also a person. You will need to use program logic to prevent different / misspellings.
The longest real life email address I've seen was 62 characters.
In exam you use the reserved word date for a column name
(subjective) I would rename applicant_date to applied_at
I don't see a postal / zip code for the applicant
All result columns are VARCHAR(4). If they use the same values, can they be normalized?
Birthdate is better to store then age. You don't want to schedule someone for an interview on their birthdate (or if you're cruel by nature, you do want that :) ). Age can be derived from it and will also be correct at all times.
EDIT:
Given that result is PASS or FAIL, simply declare the field a boolean and name it 'passed'. A lot faster.
One area where I could see a potential problem is the Interviewer being integrated in interview. Also I would like to point at the source channel in applicant, which could potentially get blobbed (depending of what you're going to store in there).
You don't seem to be violating any normalization rules upon first glance. It's not clear from your schema design, however, that the applicant_id is a referencing the applicant table. Make sure you declare it as a foreign key that references the applicant table when actually implementing the scehma.
Not to make any assumptions on your data, but can the result of a screening be stored in 4 characters?
Age and gender are generally illegal questions to ask in interviews so you may not want to record such things. You might want a separate interviewer table. You also might want a separate table that stores qualifications so you can search for people you have interviewed with C# knowledge when the next opening comes up. I'd probably do something like a Qualifications table that is the lookup for quals you want to add to the applicant qualfications table. Then you'd need the qualification id, applicantId, years, skill level in the Applicant Qualification table.
I notice results is a varchar 4 field, I assume you are planning to put Pass/fail in it. I would consider having a numeric score as well. The guy who got 80% of the questions right passed but the guy who got 100% of them right might be the better candidate. In fact for interviews I might have interview questions and results tables. Then you can record the score and any comments about each question which can help later in evaluation of a lot of candidates. We did this manually in paper spreadsheets once when we were interviewing several hundred people (we had over a hundred openings at the time and this was way before personal computers) and found it most helpful to be able to compare answers to questions. It's hard to remember 200 people you interviewed and who said what. It might help later when you have a new opening to find the people who were strong onthe questions most pertinent to the new job who might not have been given a job at the time of the interview(5 excellent candidates, 1 job for instance).
I might also consider a field to mark if the candidate is unaccepatble for ever hiring for some reason. Such as he committed a felony or he lied on the resume and you caught him or he was just totally clueless in the interview. This can make it easy to prevent this person from being considered repeatedly.
I think that your DB structure has a lot of limitation for future usage. For example you can even have a description of the exam because this stable store the score and exam date. It may by that this kind of information are already stored in another system and you have to design only the result container. But even then the exam, screen and interview are just a form of test, that why the information about should be stored in one table and distinguished by some type id. If you decide to this approach you have to create another table to store the information about result
So the definition of that should look more like this:
TEST
TEST_ID
TEST_TYPE_ID ref TEST_TYPE - Table that define the test type
TEST_REQUIRED_SCORE - The value of the score that need to be reach to pass the exam.
... - Many others properties of TEST like duration, expire date, active inactive etc.
APPLICANT_RESULTS
APPLICANT_ID ref APPLICANT
TEST_ID = ref TEST
TESTS_DATE - The day of exam
TEST_START - The time when the test has started
TEST_FINISH - The time when the test has ended
APPLICANT_RESULT - The applicant result of taken test.
This kind of structure is more flexible and give the easy way to specify the requirements between the test in table like this
TEST_REQUIREMENTS - Table that specify the test hierarchy and limitation
TEST_ID ref TEST
REQUIRED_TEST ref TEST
ORDER - the order of exams
Another scenario is that in the future your employer will want to switch to an e-exam system. In that case only think what you will need are:
Create table that will store the question definition (one question can be used in exam, screen or interview)
Crate table that will store the question answers.
Create table that will store the information about the test question.
Create table for storing the answer for each question given from applicant.
A trigger that will update the over all score of test.