Is it possible to add columns to a DBIx::Class::Row object that are virtual in that they are not saved to the database? I am looking for functionality like Rose::DB::Object provides through its non-persistent columns http://search.cpan.org/dist/Rose-DB-Object/lib/Rose/DB/Object/Metadata.pm#nonpersistent_columns
Have you tried adding methods to the Result classes in your Schema? That might get you to the same place. The methods you add can't be used in ->search and won't be returned in ->get_columns, but depending on your use case, it may be enough.
I just had to look this up again as I had a need for it. You've probably got a solution already, but for others that come here looking: https://metacpan.org/module/DBIx::Class::Manual::FAQ#Misc
Basically either use Moose and create an attribute, or add something like this to your schema:
__PACKAGE__->mk_group_accessors('simple' => qw/non_column_data/); # must use simple group
Related
I am quite new to JPA. I have a particular repository that uses the keys that have parts that are set by the caller and some values that are automatically calculated using these values. There is a need for this :)
Since the keys and entities are simple Java classes it appears to me that I need to put my code that modifies the key (or substitutes it with an internal one with additional values) is the repository implementation. However I do not think that copying the code from SimpleJpaRepository to my custom repositories is a good idea...I think that something should be possible with the entity manager. Basically what I need is proxy that gets called every time something like find() or delete() is called, takes the entity, updates its key, passes the call over to the real repository implementation.
Could someone point me to the right direction or an example that does something similar?
Thanks!
In JPA, you have a bunch of events for this, just chose the one that suits you best. It looks like you are looking for #PrePersist.
http://www.objectdb.com/api/java/jpa/annotations/callback
That said, if the data of these fields is calculated based only in the data of the other fields, it goes against database normalization. A more sensate approach would be make the calculated field #Transient and provide only the getters, that will calculate the values based in the persistent fields.
I want to be able to look through all the attributes of an Entity and find the most popular one. I know it has something to do with NSPredicate, but I can't quite wrap my mind around to achieve it.
One possible solution:
Fetch all the entities and loop through it and sort the attributes into different arrays, from there count the items in the arrays to determine the most popular/common one.
Although this might work I'm just wondering if there's an easier or 'cleaner' way of doing it.
Update:
Thanks #Caleb. Let me clarify, I'm looking for a single attribute value that's most often used by instances of a given entity.
That is really a dirty descision.
I would suggest you to make a new entity, say, AttributeCounter, with two attributes - name and count, and every time you add an attribute to a person, change this entity.
But that would only be good descision if you have a few different attributes and lots of persons. If not, here is another approach, that is quite simple:
Get all the enteties with first attribute not nil,count,add to array
Sort it
Here you are
I am struggling with how to understand the correct usage of models. Currently i use the inheritance of Db_Table directly and declare all the business logic there. I know it's not correct way to do this.
One solution would be to use Doctrine ORM, but this requires learning curve and all the current components what i use needs to be rewritten paginator and auth. Also Doctrine1 adds a another dozen classes which need to be loaded.
So the current cleanest implementation what i have seen is to use the Data Mapper classes between the so called model and DbTabel. I haven't yet implemented this as it seems to head writing another ORM. But example could be something this: SQL table User
create class with setters, getters, business logic here /model/User.php
data mapper /model/mapper/UserMapper.php, the funcionality is basically writing all the update, save actions in here.
the data source /model/DbTable/User.php extends the Db_Table_Abstract
Problems are with relationships between other models.
I have found it beneficial to not have my models extend Db_Table, but to use composition instead. That means my model 'has a' Db_Table rather than 'is a' Db_Table.
That way I find it much easier to reference multiple tables in the same model, which is a common requirement. This is enough for a simple project. I am currently developing a more complex application and have used the Data Mapper pattern and have found that it has simplified my code more than I would have believed.
Specifically, I have created a class which provides all access to the database and exposes methods such as getUser() etc.. That way, if the DB changes, or my client wants something daft like storing records in XML or we split the servers or something I only have to rewrite one class.
Again, my models do not extend this class, but have an instance of it assigned as a property during construction.
I would say the 'correct' way depends on the situation. Following the YAGNI and KISS principles, it is not good to over-complicate your model setup unless you really believe that it will benefit you in the long run.
What is the application you are developing? How is your current setup of extending Db_Table holding you back?
I have a bunch of tables mapped to ->resultset('User') and 'Tag' etc
How can I create resultset classes for querying across multiple resultset classes?
You can easily add (pseudo-code)–
$self->search_related(foreign)->search_related(original);
$self->search_related(foreign)
->search_related(many_to_many_foreign)
->search_related(foreign)
->search_related(original);
–style chains to resultset classes. This allows you to correlate/collect related data—with or without arguments—while returning a resultset of the original type. The following links give some excellent guidance. XUL isn't supported much of anywhere anymore but the plain text source is easy to read as “slides.” Some of the examples speak directly to what you’re after.
DBIx:Class Masterclass XUL slides
Somewhat crummy video of slide presentation
So, it sounds like you basically want to create a virtual view (joining your tables, etc) right?
Check out DBIx::Class::ResultSource::View if so. It'll allow you to create a virtual view resultsource, that can then be expressed through a resultset.
I can't seem to find any information in the documentation or via Google on this, but if there is something, a pointer to it would be great.
In my app, I have a Thing as a core data class. I intend to have that Thing contain many Items which has a bunch of fields in it, like order and created_date and so forth. However, there are a variety of Item types, each with their own set of fields. Ideally, I'd like to create several subclasses of Item, so that I can access all the items together in a single array or something.
In Rails, I'd use STI for this. Does Core Data support similar behaviour?
Thanks!
You can create an Item abstract entity and then have each of your unique items extend from it. Keep the relationship in the abstract so that your Thing can see all of them.
Be warned, however, that under the hood, all of those children will actually be put into a single wide table so you will need to test for performance considerations.