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.
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.
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.
The project currently I am working in requires a lot of searhing/filtering pages. For example I have a comlex search page to get Issues by data,category,unit,...
Issue Domain Class is complex and contains lots of value objects and child objects.
.I am wondering how people deal with Searching/Filtering/Reporting for UI. As far As I know I have 3 options but none of them make me happier.
1.) Send parameters to Repository/DAO to Get DataTable and Bind DataTable to UI Controls.For Example to ASP.NET GridView
DataTable dataTable =issueReportRepository.FindBy(specs);
.....
grid.DataSource=dataTable;
grid.DataBind();
In this option I can simply by pass the Domain Layer and query database for given specs. And I dont have to get fully constructed complex Domain Object. No need for value objects,child objects,.. Get data to displayed in UI in DataTable directly from database and show in the UI.
But If have have to show a calculated field in UI like method return value I have to do this in the DataBase because I don't have fully domain object. I have to duplicate logic and DataTable problems like no intellisense etc...
2.)Send parameters to Repository/DAO to Get DTO and Bind DTO to UI Controls.
IList<IssueDTO> issueDTOs =issueReportRepository.FindBy(specs);
....
grid.DataSource=issueDTOs;
grid.DataBind();
In this option is same as like above but I have to create anemic DTO objects for every search page. Also For different Issue search pages I have to show different parts of the Issue Objects.IssueSearchDTO, CompanyIssueTO,MyIssueDTO....
3.) Send parameters to Real Repository class to get fully constructed Domain Objects.
IList<Issue> issues =issueRepository.FindBy(specs);
//Bind to grid...
I like Domain Driven Design and Patterns. There is no DTO or duplication logic in this option.but in this option I have to create lot's of child and value object that will not shown in the UI.Also it requires lot's ob join to get full domain object and performance cost for needles child objects and value objects.
I don't use any ORM tool Maybe I can implement Lazy Loading by hand for this version but It seems a bit overkill.
Which one do you prefer?Or Am I doing it wrong? Are there any suggestions or better way to do this?
I have a few suggestions, but of course the overall answer is "it depends".
First, you should be using an ORM tool or you should have a very good reason not to be doing so.
Second, implementing Lazy Loading by hand is relatively simple so in the event that you're not going to use an ORM tool, you can simply create properties on your objects that say something like:
private Foo _foo;
public Foo Foo
{
get {
if(_foo == null)
{
_foo = _repository.Get(id);
}
return _foo;
}
}
Third, performance is something that should be considered initially but should not drive you away from an elegant design. I would argue that you should use (3) initially and only deviate from it if its performance is insufficient. This results in writing the least amount of code and having the least duplication in your design.
If performance suffers you can address it easily in the UI layer using Caching and/or in your Domain layer using Lazy Loading. If these both fail to provide acceptable performance, then you can fall back to a DTO approach where you only pass back a lightweight collection of value objects needed.
This is a great question and I wanted to provide my answer as well. I think the technically best answer is to go with option #3. It provides the ability to best describe and organize the data along with scalability for future enhancements to reporting/searching requests.
However while this might be the overall best option, there is a huge cost IMO vs. the other (2) options which are the additional design time for all the classes and relationships needed to support the reporting needs (again under the premise that there is no ORM tool being used).
I struggle with this in a lot of my applications as well and the reality is that #2 is the best compromise between time and design. Now if you were asking about your busniess objects and all their needs there is no question that a fully laid out and properly designed model is important and there is no substitute. However when it comes to reporting and searching this to me is a different animal. #2 provides strongly typed data in the anemic classes and is not as primitive as hardcoded values in DataSets like #1, and still reduces greatly the amount of time needed to complete the design compared to #3.
Ideally I would love to extend my object model to encompass all reporting needs, but sometimes the effort required to do this is so extensive, that creating a separate set of classes just for reporting needs is an easier but still viable option. I actually asked almost this identical question a few years back and was also told that creating another set of classes (essentially DTOs) for reporting needs was not a bad option.
So to wrap it up, #3 is technically the best option, but #2 is probably the most realistic and viable option when considering time and quality together for complex reporting and searching needs.
Essentially, I have to get a flat file into a database. The flat files come in with the first two characters on each line indicating which type of record it is.
Do I create a class for each record type with properties matching the fields in the record? Should I just use arrays?
I want to load the data into some sort of data structure before saving it in the database so that I can use unit tests to verify that the data was loaded correctly.
Here's a sample of what I have to work with (BAI2 bank statements):
01,121000358,CLIENT,050312,0213,1,80,1,2/
02,CLIENT-STANDARD,BOFAGB22,1,050311,2359,,/
03,600812345678,GBP,fab1,111319005,,V,050314,0000/
88,fab2,113781251,,V,050315,0000,fab3,113781251,,V,050316,0000/
88,fab4,113781251,,V,050317,0000,fab5,113781251,,V,050318,0000/
88,010,0,,,015,0,,,045,0,,,100,302982205,,,400,302982205,,/
16,169,57626223,V,050311,0000,102 0101857345,/
88,LLOYDS TSB BANK PL 779300 99129797
88,TRF/REF 6008ABS12300015439
88,102 0101857345 K BANK GIRO CREDIT
88,/IVD-11 MAR
49,1778372829,90/
98,1778372839,1,91/
99,1778372839,1,92
I'd recommend creating classes (or structs, or what-ever value type your language supports), as
record.ClientReference
is so much more descriptive than
record[0]
and, if you're using the (wonderful!) FileHelpers Library, then your terms are pretty much dictated for you.
Validation logic usually has at least 2 levels, the grosser level being "well-formatted" and the finer level being "correct data".
There are a few separate problems here. One issue is that of simply verifying the data, or writing tests to make sure that your parsing is accurate. A simple way to do this is to parse into a class that accepts a given range of values, and throws the appropriate error if not,
e.g.
public void setField1(int i)
{
if (i>100) throw new InvalidDataException...
}
Creating different classes for each record type is something you might want to do if the parsing logic is significantly different for different codes, so you don't have conditional logic like
public void setField2(String s)
{
if (field1==88 && s.equals ...
else if (field2==22 && s
}
yechh.
When I have had to load this kind of data in the past, I have put it all into a work table with the first two characters in one field and the rest in another. Then I have parsed it out to the appropriate other work tables based on the first two characters. Then I have done any cleanup and validation before inserting the data from the second set of work tables into the database.
In SQL Server you can do this through a DTS (2000) or an SSIS package and using SSIS , you may be able to process the data onthe fly with storing in work tables first, but the prcess is smilar, use the first two characters to determine the data flow branch to use, then parse the rest of the record into some type of holding mechanism and then clean up and validate before inserting. I'm sure other databases also have some type of mechanism for importing data and would use a simliar process.
I agree that if your data format has any sort of complexity you should create a set of custom classes to parse and hold the data, perform validation, and do any other appropriate model tasks (for instance, return a human readable description, although some would argue this would be better to put into a separate view class). This would probably be a good situation to use inheritance, where you have a parent class (possibly abstract) define the properties and methods common to all types of records, and each child class can override these methods to provide their own parsing and validation if necessary, or add their own properties and methods.
Creating a class for each type of row would be a better solution than using Arrays.
That said, however, in the past I have used Arraylists of Hashtables to accomplish the same thing. Each item in the arraylist is a row, and each entry in the hashtable is a key/value pair representing column name and cell value.
Why not start by designing the database that will hold the data then you can use the entity framwork to generate the classes for you.
here's a wacky idea:
if you were working in Perl, you could use DBD::CSV to read data from your flat file, provided you gave it the correct values for separator and EOL characters. you'd then read rows from the flat file by means of SQL statements; DBI will make them into standard Perl data structures for you, and you can run whatever validation logic you like. once each row passes all the validation tests, you'd be able to write it into the destination database using DBD::whatever.
-steve