So as a project matures it will almost certainly be necessary to modify attributes of the resource definitions to cope with additional requirements.
Let's use two trivial examples - to add a country code to a client address, or to remove a middle initial and swap in a middle name field instead.
Currently if the resource definition changes, composer won't read whatever values are extant in the repository. I didn't exhaustively try all combos, but have had to reconstitute my blockchain at least twice because of this problem.
Is there a way to mark fields either as "new" or "deprecated" to get past this that I overlooked? It will be hard to make a case to move a system that can't be changed forward to production.
In the same vein it doesn't seem to like empty or null strings much (at least for participant attributes). Having an "optional" override somewhere would save a lot of extra bounds checking in my application. Is there one of those I missed too?
So you can use the APIs or REST to expose the legacy data? You may be referring to Playground above (its not really a tool for looking at production data, its for model prototyping/sandbox/testing type stuff).
On optional question - can just add that the field is optional in the model - example here -> https://github.com/hyperledger/composer-sample-networks/blob/master/packages/pii-network/models/pii.cto#L20
Related
We want to categorize patients in our system. For example, in organ transplant, we want to "tag" a Patient FHIR resource as a donor or recipient (ignoring the scenario where a living donor can later become a recipient) since these types of "patients" are stored separately in the back end system. So when someone does a PUT HTTP request with a patient resource, we need to know what kind of patient it is before we can do the update in the database.
It's hard to determine the best way to approach this. Using the meta area seems promising, combined with the UsageContextType of "focus" perhaps, taking on values of "donor" or "recipient".
It's not clear though how to actually code something like this in a Patient resource (JSON for us). Any guidance/examples would be very much appreciated.
Sadly, I think the FHIR folks are going down the same path they used with the V3 RIM....lots of impenetrable standard definitions, but very few practical examples of how to use some of these FHIR standards in the real world. But that is another issue.
Don't understand ignoring the scenario where someone can be both donor and recipient. However, if you needed to, you could add an extension that differentiated. You could also use Patient.meta.tag.
With the RIM there'd have been an esoteric modelling mechanism to define what you wanted, likely walking through 3-4 classes to get to one element (and a whole lot of fixed values along the way). With FHIR, if you're doing something esoteric, you just define an extension.
If you see something in the core specification you find impenetrable, please submit a change request asking for the language to be improved. (There's a "propose a change" link at the bottom of every page and registration is free.)
As far as I know, POST is usually used for changing the state of the server, and PUT usually for updating the information. If I am creating a new index, should it not be POST instead of PUT? PUT does make sense when creating a document as it changes the state of data.
Your statement
As far as I know, POST is usually used for changing the state of the server, and PUT usually for updating the information.
does conform to the conventional HTTP vs CRUD semantics:
HTTP method
CRUD equivalent
Description
POST
Create
Let the target resource process the representation enclosed in the request.
PUT
Update
Set the target resource’s state to the state defined by the representation enclosed in the request.
However, the PUT spec also stipulates that:
The PUT method requests that the state of the target resource be
created or replaced with the state defined by the representation
enclosed in the request message payload
As such, PUT can (and is) used in Elasticsearch to both create an index AND update its
[settings and mappings].
Also, keep in mind that it's rarely just a matter of strict adherence to the semantics. One of the creators of ES put it this way:
It's all about REST semantics.
And our understanding of the semantics at the time when we made the APIs. And backwards compatibility constraints. And whatever "feels" natural to the person who implemented the API.
Where it makes a lot of sense Elasticsearch maps the HTTP verbs to
useful things. But when it doesn't make a ton of sense we just go with
whatever verb feels good rather than trying to be super strict about
REST. Also, we don't do linked data, instead relying on you to build
links from context. I'm told that is particularly non-REST. But it is
what we do.
It is a common practice for Restful resources to support field selectors in the query string. For example, if a resource has fields A,B,C and D but the client is interested only in a subset of fields (say A and B) then the Url might look like
.../resource/1/?fields=A,B // only A and B are 'selected'
Now supposed we add another property to the resource. The thing with this property is that it does not have any physical storage. It is a computed value. Also suppose that this computation is very expensive.
Now obviously, Rest does not care about such things, whether data comes from a file a DB or a fancy algorithm.
But here comes a dilemma: the 'fields' query parameter is always optional. In my case, omitting 'fields' means "bring all the fields" (much like '*' in SQL):
.../resource/1 // A,B,C,D and E(xpensive) are 'selected'
I am positive that there are many existing clients that are using the naive approach (not bothering to specify an explicit list of fields). This means that adding this new heavy property will unintentionally create a performance break (possibly a very severe one).
What are the common techniques to cope with these situations?
Alternatives I considered:
Add a special notion to the system that says that querying with '*' semantics will not necessarily return ALL the fields (heavy fields will be omitted by default). If a client wants them- he must ask for them explicitly
Not to model these extra properties as fields on the resource. Instead expose a dedicated endpoint that will carry out the computation, thus eliminating possible confusion but introducing Rest-RPC style into the system.
Make it the cilent's problem: if he did not bother to be explicit in the first place, tough for him. That is not really an option- don't have this privilege.
I like option 1 best. I'd consider representing these fields as referenced object, and then you could get to them HATEOAS style, through separate calls for the heavy fields. This is similar to how web-pages behave -- return the framework and some content, then force extra calls if the user wants the images, videos, etc. –
Take a look at this: spring.io/understanding/HATEOAS, this: timelessrepo.com/haters-gonna-hateoas, and this: stackoverflow.com/questions/tagged/hateoas
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.
We're looking for a way to document Core Data entities. So far the only real options I've come up with are:
Document externally using UML or some other standard
Create NSManagedObject subclasses for every entity and use code comments
Use the User Info dictionary to create a key value pair that holds a string comment
Option 1 feels like too much extra work and something that will almost certainly be out of date 99% of the time.
Option 2 feels natural and more correct than option 1. The biggest con here is that those comments could potentially be lost if this model class is regenerated using Xcode.
Option 3 feels a little less correct than option 2, but has the added advantage of adding automation possibilities with regards to meta data extraction. For instance, in one of our apps we need to keep a real close eye on what we're storing locally on the device as well as syncing to iCloud. Using the user info dictionary it's pretty easy to automate the creation of some form of artefact which can be checked both internally and externally (by the client) for compliance
So my question is whether it would be inappropriate to use the user info dictionary for this purpose? And are there any other options I'm missing?
Option 2 is what I use every time. If you look at your core data model (something.xcdatamodeld or something.xcdatamodel) you will see something like the picture below.
You can tie your entity to whatever class you want and then put the comments in there. It helps if you keep your entity name the same as your class name to make it obvious what you've done.
Additionally this also gives you the ability to add automation. You can do this by creating custom getters and setters (accessor methods) and a custom description method.
I use option 2 and categories. I'll let XCode generate the NSManagedObject subclasses and use a categorie on each of these subclasses. With the categories I do not loose my changes made in the categories, can document, make custom getter and setters and I am still able to use generated subclasses.
If we speak only about documenting (i.e. writing more or less large amounts of text which is intended to be read by humans) your classes, I'd use the option 2.
If you are concerned with the possibility of Xcode overwriting your classes in the option 2, you may consider creating two classes for each entity: one which is generated by Xcode and always could be replaced (you generally do not touch this file) and one other which inherits from the generated one and in which you put all your customizations and comments.
This two-class approach is proposed by the mogenerator.
Although if you need to store some metadata with the entities which will be processed programmatically, the userInfo is perfectly suitable for this.