For example storing the different phone numbers that a person might be contacted on. If I do not want my database to be restricted to allow fixed, say 6, numbers per person then the only solution to the problem seems to be to have a separate table and have multiple records for one person.
eg
person1, p1number1
person1, p1number2
person2, p2number1
person1, p1number3
.
.
.
...
and so no.
But in a practical scenario this kind of table might become very large. So is this approach better or one should not be thinking of storing multivalued attributes in an RDBMS at all?
This is perfectly normal; breaking out a new table is better than adding innumerable fields to an existing one, IMO. Normally this is done with an FK pointing at person_id, say. Practically speaking, these tables tend not to actually get THAT large.
It's just more work.
You can always fall back to comma separated values if you don't like separate table.
Related
I have a situation as described in the ExtbaseFluid book:
I would like to store information in the intermediate table which is not recommended at all.
Here is a cite from the warning box of the above linked book chapter:
Do not store data in the Intermediate Table that concern the Domain. Though TYPO3 supports this (especially in combination with Inline Relational Record Editing (IRRE) but this is always a sign that further improvements can be made to your Domain Model. Intermediate Tables are and should always be tools for storing relationships and nothing else.
Let’s say you want to store a CD with its containing music tracks: CD -- m:n (Intermediate Table) -- Song. The track number may be stored in a field of the Intermediate Table. However, the track should be stored as a separate domain object, and the connection be realized as CD -- 1:n -- Track -- n:1 -- Song.
So I want not to do what is not recommended. But thinking about the workflow for the editor that results of the recommended solution rises a few question for me.
To stay with this example I would need the following tables:
tx_extname_domain_model_cd
tx_extname_domain_model_cd_track_mm
tx_extname_domain_model_track (which holds the track number)
tx_extname_domain_model_track_song_mm
tx_extname_domain_model_song
From what I know this would end in the situation that the editor would need to create following records:
one record for the cd
one record for the song
now the editor can create one record for the track.
There the track number is added.
Furthermore the cd record needs to be assigned as well as the song.
So here are my questions:
I guess this workflow cannot be improved with some (to me unknown) TCA setup?
An editor cannot directly reach the song when the cd record is opened?
Instead first she / he has to open the track record and can from there navigate to the song?
Is it really that bad to store data in the intermediate table? The TYPO3 table sys_file_reference does the same!? But I wonder how those data could be shown (because IRRE is not possible because it shall only be used for 1:n relations (source).
The question you have to ask yourself is: Do I want to do coding by the book, or do I want to create a pragmatic approach to solve a customer's problem?
In this specific case the additional problem is, that the people who originally invented Extbase had a quite sophisticated and academic approach, but when it comes to a pragmatic use and performance, they were blocked by their own rules and stuck with coding by the book.
Especially this example and the warning message shows a way of thinking that was one of the reasons, why I never actually used Extbase but went for Core-API methods to create performant and pragmatic queries to get the desired result sets. Now that we've got Doctrine under the hood, this works like a charm even with quite exotic DB flavors.
Of course intermediate tables are a good idea and of course those intermediate tables can and should be enriched with additional data fields, that do not require a 3rd, 4th or nth table to store i.e. a simple set of dropdown options, since this can easily be handled with attributes configured in TCA, as it is shown here: https://docs.typo3.org/m/typo3/reference-tca/master/en-us/ColumnsConfig/Type/Inline/Examples.html
sys_file_reference is the most prominent example since it provides exactly that kind of additional information that should not be pumped into additional tables - and guess what, the TYPO3 core does not make use of a single line of Extbase code to deal with that data or almost any other data of the core tables.
To answer your last question: Take a look at the good old IRRE Tutorial to get a clue how to do m:n connections with intermediate inline tables.
https://docs.typo3.org/typo3cms/extensions/irre_tutorial/0.4.0/Manual/Index.html#intermediate-tables-for-m-n-relations
Depends on the issue, sometimes the intermediate table is an entity, sometimes not. In this example the intermediate table is the track, which would contain: [uid, cd, song, track_no, ... (whatever else needed to define the track)]
Be carefull when you define your data, that you do not make it too advanced.
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 am working on an app where I use core data.
I already have tried to do it with one entity but that didn't work.
But I now have like twenty entities and my question is: is there a limit to the number of entities or a number recommended?
Is there a better way to store that amount of data?
UPDATE:
What I am storing are grads from school but not the A,b,c,d,e,f but a number from 1 to 10. And each grad has is own weighing(amount of times a number count) like some grad count 2 time because the are more imported.
So i first thought to have an array with a string for the name of the subject and then to array one store's the grad the other the corresponding weighing.
Like this:
var subjects: [String,[Int],[Int]]
but this isn't possible and I don't even know how I should put this in core data and get it back properly.
Because I couldn't figure it out, I thought of just making a entity for each subject but there are a lot of them so there for this question.
There's no limit to the number of entities, but it's possible to go overboard and create more than you actually need. The recommended number is "as many as you need and no more", which obviously will vary a great deal depending on the nature of the data and how the app uses it. Whether there's a better way than your current approach is totally dependent on the fine details of exactly what you're doing, and so is impossible to answer without a far more detailed question.
You could setup a Subject entity that has one-to-many relationships to ordered sets of Grade and Weight, like so:
However, each grade apparently has a corresponding weight, so it would be more accurate to store each grade's weight in the Grade entity:
This still may not represent your real-world model.
If your subject is something general, like math or english, you could have more than one subject per grade, (e.g., algebra, geometry, trigonometry), or more than one level per subject (e.g., algebra 1, algebra 2) which may or may not have a different grade.
If your subject is very specific, your data may end up spread across unique one-to-one relationships, instead of one-to-many relationships.
You would also need to consider whether you can use ordered or unordered relationships, or whether an attribute exists that you can use to sort an entity.
You should consider these different facets of what you're trying to model (as well as the specific fetches you'd want to perform), before you try to design or implement the model, to allow you to efficiently represent this particular object graph.
What are some possible designs to deal with frequently changing data forms?
I have a basic CRUD web application where the main data entry form changes yearly. So each record should be tied to a specific version of the form. This requirement is kind of new, so the existing application was not built with this in mind.
I'm looking for different ways of handling this, hoping to avoid future technical debt. Here are some options I've come up with:
Create a new object, UI and set of tables for each version. This is obviously the most naive approach.
Keep adding all the fields to the same object and DB tables, but show/hide them based on the form version. This will become a mess after a few changes.
Build form definitions, then dynamically build the UI and store the data as some dictionary like format (e.g. JSON/XML or maybe an document oriented database) I think this is going to be too complex for the scope of this app, especially for the UI.
What other possibilities are there? Does anyone have experience doing this? I'm looking for some design patterns to help deal with the complexity.
First, I will speak to your solutions above and then I will give my answer.
Creating a new table for each
version is going to require new
programming every year since you will
not be able to dynamically join to
the new table and include the new
columns easily. That seems pretty obvious and really makes this a bad choice.
The issues you mentioned with adding
the columns to the same form are
correct. Also, whatever database you
are using has a max on how many
columns it can handle and how many
bytes it can have in a row. That could become another concern.
The third option I think is the
closest to what you want. I would
not store the new column data in a
JSON/XML unless it is for duplication
to increase speed. I think this is
your best option
The only option you didn't mention
was storing all of the data in 1
database field and using XML to
parse. This option would make it
tough to query and write reports
against.
If I had to do this:
The first table would have the
columns ID (seeded), Name,
InputType, CreateDate,
ExpirationDate, and CssClass. I
would call it tbInputs.
The second table would have the have
5 columns, ID, Input_ID (with FK to
tbInputs.ID), Entry_ID (with FK to
the main/original table) value, and
CreateDate. The FK to the
main/original table would allow you
to find what items were attached to
what form entry. I would call this
table tbInputValues.
If you don't
plan on having that base table then
I would use a simply table that tracks the creation date, creator ID,
and the form_id.
Once you have those you will just need to create a dynamic form that pulls back all of the inputs that are currently active and display them. I would put all of the dynamic controls inside of some kind of container like a <div> since it will allow you to loop through them without knowing the name of every element. Then insert into tbInputValues the ID of the input and its value.
Create a form to add or remove an
input. This would mean you would
not have much if any maintenance
work to do each year.
I think this solution may not seem like the most eloquent but if executed correctly I do think it is your most flexible solution that requires the least amount of technical debt.
I think the third approach (XML) is the most flexible. A simple XML structure is generated very fast and can be easily versioned and validated against an XSD.
You'd have a table holding the XML in one column and the year/version this xml applies to.
Generating UI code based on the schema is basically a bad idea. If you do not require extensive validation, you can opt for a simple editable table.
If you need a custom form every year, I'd look at it as kind of a job guarantee :-) It's important to make the versioning mechanism and extension transparent and explicit though.
For this particular app, we decided to deal with the problem as if there was one form that continuously grows. Due to the nature of the form this seemed more natural than more explicit separation. We will have a mapping of year->field for parts of the application that do need to know which data is for which year.
For the UI, we will be creating a new page for each year's form. Dynamic form creation is far too complex in this situation.
When creating a web application that some how displays the display of a unique identifier for a recurring entity (videos on YouTube, or book section on a site like mine), would it be better to use a uniform length identifier like a hash or the unique key of the item in the database (1, 2, 3, etc).
Besides revealing a little, what I think is immaterial, information about the internals of your app, why would using a hash be better than just using the unique id?
In short: Which is better to use as a publicly displayed unique identifier - a hash value, or a unique key from the database?
Edit: I'm opening up this question again because Dmitriy brought up the good point of not tying down the naming to db specific property. Will this sort of tie down prevent me from optimizing/normalizing the database in the future?
The platform uses php/python with ISAM /w MySQL.
Unless you're trying to hide the state of your internal object ID counter, hashes are needlessly slow (to generate and to compare), needlessly long, needlessly ugly, and needlessly capable of colliding. GUIDs are also long and ugly, making them just as unsuitable for human consumption as hashes are.
For inventory-like things, just use a sequential (or sharded) counter instead. If you migrate to a different database, you will just have to initialize the new counter to a value at least as large as your largest existing record ID. Pretty much every database server gives you a way to do this.
If you are trying to hide the state of your counter, perhaps because you're counting users and don't want competitors to know how many you have, I suggest avoiding the display of your internal IDs. If you insist on displaying them and don't want the drawbacks of a hash, you might consider using a maximal-period linear feedback shift register to generate IDs.
I typically use hashes if I don't want the user to be able to guess the next ID in the series. But for your book sections, I'd stick with numerical id's.
Using hashes is preferable in case you need to rebuild your database for some reason, for example, and the ordering changes. The ordinal numbers will move around -- but the hashes will stay the same.
Not relying on the order you put things into a box, but on properties of the things, just seems.. safer.
But watch out for collisions, obviously.
With hashes you
Are free to merge the database with a similar one (or a backup), if necessary
Are not doing something that could help some guessing attacks even a bit
Are not disclosing more private information about the user than necessary, e.g. if somebody sees a user number 2 in your current database log in, they're getting information that he is an oldie.
(Provided that you use a long hash or a GUID,) greatly helping youself in case you're bought by YouTube and they decide to integrate your databases.
Helping yourself in case there appears a search engine that indexes by GUID.
Please let us know if the last 6 months brought you some clarity on this question...
Hashes aren't guaranteed to be unique, nor, I believe, consistent.
will your users have to remember/use the value? or are you looking at it from a security POV?
From a security perspective, it shouldn't matter - since you shouldn't just be relying on people not guessing a different but valid ID of something they shouldn't see in order to keep them out.
Yeah, I don't think you're looking for a hash - you're more likely looking for a Guid.If you're on the .Net platform, try System.Guid.
However, the most important reason not to use a Guid is for performance. Doing database joins and lookups on (long) strings is very suboptimal. Numbers are fast. So, unless you really need it, don't do it.
Hashes have the advantage that you can check if they are valid or not BEFORE performing any check to your database whether they exist or not. This can help you to fend off attacks with random hashes as you don't need to burden your database with fake lookups.
Therefor, if your hash has some kind of well-defined format with for example a checksum at the end, you can check if it's correct without needing to go to the database.