I have a basic news extension with a m:m relation to the fe_users table.
This relation is used for knowing which user accessed which news, so when the user accesses the details view of some news, an entry is added in the MM table.
What I want also, is to have a int field (a unix timestamp) which tells when the user accessed the news.
I know I could just add a TIEMSTAMP field with CURRENT_TIMESTAMP as default, but I may have to add other information beside it, so how could I do this?
Thank you.
How about creating a e.g. Visitation Object wich stores the user, a timestamp and all the information you'd like and make a mm relation to this table instead ob fe_users?
Related
I want to create an application for enabling the users to book the computers in a laboratory if they want to use it from a specific time to time.The users can book the computers for their next 15 days. So,how should I design the database for this application.
Start by defining what your entities and attibutes will be. It's better if you can do a Conceptual Design first.
Than you design it logically.
For example, your entities might be:
USERS, COMPUTERS, RESERVATIONS.
Your attributes might be:
USERS (SomeUniquePersonalIDnumber, Name, Surname, Email*, PhoneNumber*)
PrimaryKey in bold. With asterisk *Optional
COMPUTERS (UniqueComputerSerialNumber, NumberOfComputerInLab)
RESERVATIONS (AutoincrementNumber, UserPK, ComputerPK, DateOfReservation, TimeFrom, TimeTill)
PrimaryKey composed of the three attibutes making it unique. Same user might reserve the same computer over time but the AutoincrementNumber field will make the composite PK unique.
RESERVATIONS(UserPK) referencing USER(SomeUniquePersonalIDnumber)
RESERVATIONS(ComputerPK) referencing COMPUTERS(UniqueComputerSerialNumber)
Define what type of fields will those attributes be
(Integer/Varchar/...) based on the querying language you will want
to use.
Translate all of above into commands to create the database, the
tables etc.
Just pick a piece of paper and start with normalization https://en.wikipedia.org/wiki/Database_normalization.
If I look for entities in your question I see the following entities:
user
computer
booking
Then you need to figure out what properties belong to those entities and the relation between them. You can create an ERD if you like and start creating Ruby on Rails models.
In Ruby on Rails if you generate a model the model has a created_at datetime field by default. I think you can use that to figure out the specific time and check if 15 days are past since this booking is created.
I have a Rails app that is basically designed this way:
It has a Book model, that has an external_id (all saved Book records have an external_id). The external_id links to an external source about books that doesn't allow for the data to be stored. We use a Presenter to handle some of the differences in the Book model and the external library's class to smooth things over for the view.
We let users do things like "Favorite" their books, regardless of source, so we have a join table and model with a book_id and a user_id to record favorites.
However, in some of the queries, there will be a list of results displayed to the user from the external source, even though we might have Book records with those external_ids. We want to be able to display information like who that the user is friends with that has favorited that book.
It seems there are a couple of ways to handle this:
1) Always load the canonical Book record (if it exists) in the presenter based on the external_id, and override the Book#friends_who_favorited method to return false if no external_id was found
2) Overload the presenter to either call Book#friends_who_favorited or if not a Book record, create its own join query based on external_id (since we wouldn't know the book id yet).
3) Denormalize the database a little, and make sure that we always store the external_id everywhere -- Basically treat external_id like the primary key since every Book record has an external_id. Then the queries can be done more directly, not require a join query, and we wouldn't need multiple queries written. But, this ties us even more to that external source since now our database design will be based on external_id.
It seems like #1 might be the best way to do it, even though it would introduce an extra query to Book (Book.where(external_id: x).first), since #2 would require writing a whole set of additional queries to handle the external_id case. But, I'm open to suggestions as I'm not fully comfortable with any of these methods.
Based on the discussions, if I do that I might consider this solution:
Setup
Uniform the identifier of all books to an id instead of ActiveRecord default id. This is the current field external_id, though I would prefer to rename it without underscore, say rid represents resource id.
Use a format for internal books on rid different from external books.
For example, suppose the format of external id like "abcde12345", then you name the internal books rid as "int_123" according to actual id so all of them are guaranteed to be unique.
Use a model callback to update rid after creating. If it's internal, copy its id and add "int_" prefix. If it's external, save its external id to that field.
Usage
Now usage would be simpler. For every action, use rid instead of original id. When an user favouring the book, the association would be the rid.
In the join table, you can also keep the original id there, so that when one day you changed implementation, there would still be original ids available.
Now the join table will have 4 fields: id, user_id, book_id(the original id), book_rid.
To display the users who liked this book, no matter the book is external or not, you can now query based on the rid in join table and fulfil the job.
Refacoring
Actually refacoring on this solution should not be hard and do no harm.
Add a field rid in the join table
Build a query task to fill rid of all books. Actually it's for internal books only which has blank external_id at this moment.
Build a query to fill the rid field in join table.
Refacor associating method to specify association id, and other related methods if needed.
I'll try to be short and clear with this question.
We have an asp.net mvc app that uses entity framework 4.
Our business model is relatively straightforward:
We have an object (which corresponds to a table) called Photo(s).
That photos table has a handful of columns that match up to properties on the object.
Description,Title,Date etc.
It also has a number columns that reference foreign keys for other tables:
AuthorId,LicenseId etc...
The author and license tables are complex in their own right, with multiple fields (Title,Summary,Date etc.)
I have multiple clients using this application to view their photos. I would like each client to dictate what fields they see when viewing the photos, as well as what fields they see when editing those fields.
My thought is to have tables setup saying client-a should see Field1,Field2 and Field3 when viewing their photos - and client-b should see Field1,Field4 and Field5. But some of these fields are not simply columns in the main photos table, they may be fields in a child table. so Field1 might be: Table.Photos.Title -> which corresponds to an object as: Objects.Photo.title...
but Field3 might be: Table.Licenses.LicenseSummary -> which corresponds to an object as: Objects.Photo.License.LicenseSummary
I'm trying to figure out the methodology that we would use to have a very data driven environment so in the DB I can say, display this object/property (for viewing or editing) and then it would know how to map to whatever table it needs to pull that information. also, during editing... give it some way to pull a list of available values if it is that type of property, and not just a text field.
I'm looking for an example of what this might involve, our model is actually more complex than this, but this is just an idea of what we are trying to accomplish. I don't know if what I'm trying to do is normal, perhaps it involves reflection? This is a new area for me.
If the clients are defining their own custom fields, I would simply give them a Key/Value pairs table.
PhotoID FK
Key string
Value string
Display bool
Note that this essentially amounts to EAV, which comes with its own set of difficulties.
If it's just about permissions on existing fields, you need to capture that information:
PhotoID FK
ClientID FK
FieldName string
Display Bool
You can use this information to inhibit the display of fields in the View. The easiest way to do that would be to use a loop in the View itself, writing the field to the output only if Display is set to true.
I have a custom membership provider which I extended - added a couple of fields, first name, last name, adress, zip code and city.
now, these fields reside in the aspnet_Membership table so that I can easily access them when using the static Membership asp.net class.
now, I want to be able so save customer purchase order data (first name, last name, adress, zip code and city) to the database.
should I in my order model/table use a new set of fields - first name, last name, adress, zip code, city or should I create a relationship between my asp_Membershihp table and my Orders table?
Also, If i have dupe data, once a users asks for his account to be removed I wont have any orphan rows in my Orders table if I use the first method.
so, which is best, to have the user data, first name, last name, adress, zipcode, city in only one table and create a relationship between aspnet_Membership table and Orders table OR create the dupe fields in my Orders table with no relationship to the aspnet_Membership table? Pros cons?
Thanks!
/P
In this scenario, i would rather have the relationship.
Also being the data you are storing Orders (i assume at least, from the name :)) i would maintain a separate set of data on the Order, so one would optionally be able to specify different billing/shipping data than it's Identity on the site.
Another valid reason for duplicate at least some data on the Order table is to have all the necessary data relevant to an Order in the table, thus avoiding problems if the Client request his data to be deleted, and maintain the original values for that data on the order if the customer data were to change in time.
If you are able to, though, you should not actually delete User data, but have a field in which you specify if the User isActive or isDeleted.
I'm creating a web application with grails, and I'm working on the CRUD prototype using Scaffold. Out of the box, the scaffold will use the unique id (which makes sense) for foreign key values, and I'm wondering if I can easily replace the unique id with a readable value (such as a combination of two values from said table).
For example:
I have Location and RoomNumber domains that represent a Hotel location and room number. Each number therefore "belongs-to" a location. When I go to create a room, I have a drop-down auto-generated that allows me to pick from existing locations. These are unintuitive values though... such as "project.Location : 1"
I'd like to replace this "project.Location : 1" with the name, city, and state column values that correspond to id 1. Is this an easy thing to modify? I'd think there's some simple mapping that needs to be done...
Thanks in advance!
Turns out the solution is really simple... just need to implement the toString method in the corresponding Domain class. Received this answer from the Grails mailing list.