Lets say we have a class "Car" than has different pieces of data ( maker, model, color, fabrication date, registration date, etc). The class has no method to get data, but it knows to as for it from another object (sent via constructor, let's cal it for short DS).- and the same for when needing to update changes.
A method getColor() would be implemented like this
if(! this->loaded('color')){
this->askDS('color') // this will do the necesarry work to generate a request to DS
}
return this->information('color');
Nothing too fancy so far. No comes the part i want to find out if it has a name, or if there are libraries / frameworks that do this already.
DS has a list of methods registered dinamically based on the class that needs data. For car we have:
input: car serial number, output: method to use to read the numbers to extract raw values
input: car raw color value, output: color code
input: car color code, manufacturer, year, mode, output:human-readable color (for example navy blue)
Now, DS or any method does not have an ordered list of using command to start from serial number and return the color blue, but if can construct a chain of methods that from one set of data, it can run them in order and get the desired data.
For our example above, DS runs 1,2,3 in that order and injects the data resulted from all methods into the class object that needed it.
Now if the car needs registration info, we have method (4) that gets that from the police database with an api request.
So, given:
- a type of model (class/object)
- a list of methods that take a fixed list of input(object properties) and give out a fixed list of output (object properties)
- a class DS that can glue the methods and run the needed ones for a model to get from property A (serial) to properby B (human readable colour) without the model or DS having a preconfigured way to get this data but finding it as needed.
does this have a name or is it already implemented somewhere ?
I've implemented a very basic prototype and it works very nice and i think this implementation method has useful features:
if you have a set of methods that do sql queries and then your app switches to using an api, you only need to change the methods and don't have to touch any other part of the application
when looking for a chain of methods that resolve the 'need' the object has, you can find a method chain, run it, if it fails keep looking for another list of methods based on the currently available data - so if you have multiple sources for a piece of data, it can try multiple versions
starting from the above paragraph i could start with an app that only has sql queries for data retrieval - when i find out a part of the app overloads the sql server i could add a method to retrieve data from cache with a lower cost than the one from database (or multiple layered caches, each with different costs)
i could probably add business logi in the mix the same ways as cache, and based on the user location / options present different data
this requires less coding overall, and decouples the data source from the object, making each piece easier to mock/test
what is needed to make this fast is a caching solution for the discovered method chains, since matching hundreds of thousands of methods per model type would be time-consuming but I don't think this is very hard to do - just store all found chains in memory as you find them and some metadata to be able to resume a search from any point in time - when you update the methods, just clear the cache, take a performance hit for the first requests
Thank you for your time
What you describe sounds like a somewhat roundabout way of doing Dependency Injection. Quote:
"Passing the service to the client, rather than allowing a client to
build or find the service, is the fundamental requirement of the
pattern."
Depending on what language you're using, there should be several Dependency Injection frameworks/libraries available.
Related
Not sure this is specific to Laravel but what is the proper RESTFUL way to handle creating a child of a parent with Laravel. For example I have a Car that can have many Drivers (hasMany) and Drivers belong to one Car (belongsTo). If I want to create a Driver whose parent is Car #1 does the CarController.php have the responsibility to create the driver: /car/1/driver/create or do I use /driver/create/car/1 and keep the responsibility within DriverController.php?
Right now I'm doing /driver/create/1 (where #1 represents the Car) which feels wrong but I'm not clear about what the RESTFUL way should be. TIA.
There really isn't a proper way of implementing nested resources in REST as it doesn't really care. There are arguments for and against nested resources, however, there are some generally accepted implementations and the agreement that whatever you decide on, be consistent.
I utilise nested resources, but only a single level of nesting and no more. So for example:
GET /cars/{carId}/drivers/{driverId}
However, I would avoid the following:
GET /cars/{carId}/drivers/{driverId}/incidents
If you have multiple nested resources, consider obtaining the nested resource through the parent resource:
GET /cars/{carId}/drivers/ // Get all drivers for the car
GET /drivers/{driverId}/incidents // Get all incidents for the driver
Arguably nested resource URLs can convey more meaning than a single resource URL at a glance. e.g.
GET /cars/{carId}/drivers/{driverId} // more meaningful
GET /drivers/{driverId} // less meaningful
With the second URL above, I do not know which car the requested driver is associated with until the resource is returned. That being said /drivers/{driverId} can still be applicable and useful to have depending on your use case.
A use case for a /drivers endpoint would be if you can create new drivers that are not yet associated with a car.
In response to your question of how to create a driver, I would consider the following use cases;
Create a driver without an association to a car
POST /drivers
Create a driver with an association to a car
POST /cars/{carId}/drivers
POST /drivers
For the POST /drivers endpoint you would use a DriverController and pass your Driver information to the store method. The validation rules in the store method would allow for an optional car_id parameter as part of the request. This would allow you to either associate a driver with a car at creation, or not.
For the POST /cars/{carId}/drivers endpoint, you would use a CarDriverController (or a DriverController in a Cars subfolder if often seen) and pass your Driver information to the store method. A car_id paramter would not be required in the request as the associated car would be obtained from the {carId} passed in the URL.
For updating your driver resources, you can follow the same principle just amending your HTTP verbs and creating the appropriate routes.
PUT /drivers/{driverId}
DriverController#update
PUT /cars/{carId}/drivers/{driverId}
CarDriverController#update
If you decided to implement both methods for creating drivers and you find duplicate code, consider refactoring it to a service.
Update 1
For #2 POST /cars/{carId}/drivers is the store endpoint does that make GET /cars/{carId}/drivers/create the create endpoint? And similarly for POST /drivers creation endpoint GET /drivers/cars/{carId}?
If you're working with blade views and following the Laravel conventions then your form to create a new driver for a given car would be found at GET /cars/{carId}/drivers/create or GET /drivers/create.
And it sounds like relationships should always get a separate controller.
Ideally yes as most applications are nothing more than CRUD and so everything can be mapped to one of the 7 controller actions. This keeps things clean and simple and responsibilities separate.
Take a look at this video by Adam Wathan which explains how to map what you think are custom actions to one of the 7 basic Laravel actions. Bit lengthy at 40 minutes but well worth a watch.
POST /cars/1/driver.
no interest in specifying the action (create). the method (post) already does it.
I have developed a system where various classes have attributes consisting of a custom formula. The formula can contain special tokens which refer to different types of object. For example an object of class FruitSalad may have the following attribute;
$contents = "[A12] + [B76]";
In somewhat abstract terms, this means "add apple 12 to banana 76". It can also get significantly more complex than that with as many as 15 or 20 references to other objects involved in one formula.
I have a trait which passes formulae such as this and each time it finds a reference to a model (i.e. "[A12]") it gets it from the database with A::find(12) and adds it to an array of component objects which can be used for other processes later on in the request.
So, in essence, it's a relationship. But instead of a pivot table to describe the relationship, there is a formula on the parent model which can include references to child models.
This is all working. Yay! But it's really inefficient because there are so many tiny queries to get single models as formulae are parsed. One request may quite easily result in hundreds of queries. Oops.
I see two potential options;
1. Get all my apples and bananas from the database at the start of the request and get them from an in-memory store instead of from the database when parsing a formula (is this the repository pattern??).
2. Create a custom relation type (something like hasManyFromFormula) which makes eager loading work so that the parsing becomes much simpler because the relevant apples and bananas would already be loaded into the parent model.
Is there a precedent for this? As for why I am doing it like this, it would a bit tough to explain in brief but suffice to say it is to support a highly configurable data retrieval system which supports as-yet unknown input data configurations.
Help!
Thanks,
Geoff
Am not completely sure if it is the best solution, but in the end I created a new directory class for basic components and then set it up in the app service provider as a singleton. The constructor for the directory class loaded all models of several relevant classes and made them available as collections throughout the app.
I think this should be an easy one, but haven't found any clear answer, on what would the best practice be.
In an application, we keep current status of an order (open, canceled, shipped, closed ...).
This variables cannot change without code change, but application should meet the following criteria:
status names should be easily displayed in different languages,
application can search via freetext status names (like googling for "open")
status_id should be available to developer via enum
zero headache when adding new statuses
Possible ways we have tackled this so far:
having DB table status with PK(id, language_id) and a separate enum which represents this statuses in an application.
PROS: 1.,2.,3. work out of the box, CONS: 4. needs to run update script on every client installation, SQL selects can become large and cumbersome, when dealing with a lot of code tables
having just enum:
PROS: 3.,4. CONS: 1.,2. is a total nightmare
having enums, which populate database tables on each start of an application:
PROS: 1.,2.,3.,4. work CONS: some overhead on application start, SQL select can become large and cumbersome, when dealing a lot code tables.
What is the most common way of tackling this problem?
Sounds like you summarized it pretty good yourself, and comparing the pros/cons points towards #3. Just one comment when you implement #3 though:
Use a caching mechanism (even a simple HashMap!) plus adding the option to refresh the cache - will ease your work when you'll want to change values (without the need to restart every time!).
I would, and do, use method 3 because it is the best of the lot. You can use resource files to store the translations in and map the enum values to keys in the resource files. Your database can contain the id of the enum for the status.
1.status names should be easily displayed in different languages,
2.application can search via freetext status names (like googling for "open")
These are interfaces layer's concern, you'd better not mix them in you domain model.
I would setup a mapping between status enum and i18n codes. the mapping could be stored in a file (cached in memory) or hardcoded.
for example: if you use dto or view adatper to render your ui.
public class OrderDetailViewAdapter {
private Order order;
public String getStatus() {
return i18nMapper.to(order.getStatus());//use hardcoded switch case or file impl
}
}
Or you could done this before you populating you dtos.
You could use a similar solution for goal2. When user types text, find corresponding enum from mapping and use enum for search.
Anyway, use db tables the less the better.
Personally, I always use dedicated enum class inside domain. Only responsibility of this class is holding status name (OPEN, CANCELED, SHIPPED, ...). Status name is not visible outside codebase. Also, status could be also stored inside database field as string (varchar or similar).
For the purpose of rendering, depending of number of use cases, sometimes I implement formatting inside formatter (e.g. OrderFormatter::formatStatusName(), OrderFormatter::formatAbbreviatedStatusName(), ...). If formatting is needed often I create dedicated class with all formatting styles needed (OrderStatusFormatter::short(), OrderStatusFormatter::abbriviated()...). Of course, internal mapping is needed to map status name to status title, and this is tricky part. But if you want layering you can't avoid mapping.
Translation is not dealt so far. I translate strings inside templates so formatters are clean of that responsibility. To summarize:
enum inside domain model
formatter inside presentation layer
translation inside template
There is no need to create special table for order status translations. Better choice would be to implement generic translation mechanism, seperated from your business code.
I have this idea of generating an array of user-links that will depend on user-roles.
The user can be a student or an admin.
What I have in mind is use a foreach loop to generate a list of links that is only available for certain users.
My problem is, I created a helper class called Navigation, but I am so certain that I MUST NOT hard-code the links in there, instead I want that helper class to just read an object sent from somewhere, and then will return the desired navigation array to a page.
Follow up questions, where do you think should i keep the links that will only be available for students, for admins. Should i just keep them in a text-file?
or if it is possible to create a controller that passes an array of links, for example
a method in nav_controller class -> studentLinks(){} that will send an array of links to the helper class, the the helper class will then send it to the view..
Sorry if I'm quite crazy at explaining. Do you have any related resources?
From your description it seems that you are building some education-related system. It would make sense to create implementation in such way, that you can later expand the project. Seems reasonable to expect addition of "lectors" as a role later.
Then again .. I am not sure how extensive your knowledge about MVC design pattern is.
That said, in this situation I would consider two ways to solve this:
View requests current user's status from model layer and, based on the response, requests additional data. Then view uses either admin or user templates and creates the response.
You can either hardcode the specific navigation items in the templates, from which you build the response, or the lit of available navigation items can be a part of the additional information that you requested from model layer.
The downside for this method is, that every time you need, when you need to add another group, you will have to rewrite some (if not all) view classes.
Wrap the structures from model layer in a containment object (the basis of implementation available in this post), which would let you restrict, what data is returned.
When using this approach, the views aways request all the available information from model layer, but some of it will return null, in which case the template would not be applied. To implement this, the list of available navigation items would have to be provided by model layer.
P.S. As you might have noticed from this description, view is not a template and model is not a class.
It really depends on what you're already using and the scale of your project. If you're using a db - stick it there. If you're using xml/json/yaml/whatever - store it in a file with corresponding format. If you have neither - hardcode it. What I mean - avoid using multiple technologies to store data. Also, if the links won't be updated frequently and the users won't be able to customize them I'd hardcode them. There's no point in creating something very complex for the sake of dynamics if the app will be mostly static.
Note that this question doesn't quite fit in stackoverflow. programmers.stackexchange.com would probably be a better fit
I'm building a report that needs to include an 'estimate' column, which is based on data that's not available in the dataset.
Ideally I'd like to be able to define a Java interface
public int getEstimate(int foo_id, int bar_id, int quantity);
where foo_id, bar_id and quantity are available in the row I want the estimate presented.
There will be multiple strategies for producing the estimate so it would be good to use an interface to allow swapping them when needed.
Looking at the BIRT docs, I think it's possible I ought to be using the event handler mechanisms, but that seems to only allow defining a class to use and I'd somehow like to inject a configured estimator.
A non-obfuscated example might be to say that I have a dataset which includes an IP address column, and I'd like to be able to use some GeoIP service to resolve the country from the IP address. In that case I'd have an interface public String getCountryName(String address) and the actual implementations may use MaxMind, a local cache or some other system.
How would I go about doing this?
Or.. would I be better off by writing a scripted data source that can integrate the computed data before delivering it to BIRT?
Or.. some sort of scripted data source that is then used to create a join data set?
I think a Scripted Data Source would work fine, but a Java-based event handler would be more straightforward. You can implement it as a simple POJO and get access to any and all the complex objects and tools that will allow you to calculate your estimate. The simplest solution of all may simply to be adding a calculated field to the data set.
When creating the calculated field, you can get pretty complex in terms of the scripting logic you can leverage in order to produce the resultant value. The nicest thing about this route is that all the other column values in the row (which I assume you need to calculate the estimate) are made available via the Expression editor. You can pull in complex objects (POJOs) to help in your calculations here as well by using the "Packages" object (i.e. var red = new Packages.redwood.HelloWorld())
If you want to create the Event Handler class, here is what I would do. I would create a text object and bind the onCreate even to your POJO (by extending the TextItemEventAdapter) and override the "onCreate" method. There you can do any work you want to and at the end simply call 'text.setText(theEstimateResult);' to make the estimate itself visible. As far as accessing data values to do your calculations, You can get to those in the POJO too. I assume the estimate will be a part of a larger table of values. You can access any specific row value via the reportContext.
Those are the two ideas I would give a try first. The computed column is the fastest to implement and the least likely to throw you a curve during deployment. Let me know which way you choose and we can hash it out further if needed.