I have a page named "ReportController.aspx" whose purpose is to instantiate a report (class) based on query string parameters
switch (Request.QueryString["Report"])
{
case "ReportA":
CreateReportAReport("ReportA's Title");
break;
case "ReportB":
CreateReportBReport("ReportB's Title");
break;
case "ReportC":
CreateReportCReport("ReportC's Title");
break;
case "ReportD":
CreateReportDReport("ReportD's Title");
break;
...
Basically, each time a new report is needed there will be this overhead of adding a case and adding a method. This switch statement could get very very long. I read that is is possible to use a Dictionary to map a Report to ?. How would this look using a Dictionary (assuming this is a better way).
Also, CreateReportXReport method basically passes a bunch of additional QueryString values to the report class's constructor (each report class has a different constructor).
There's no getting around having to type in the new information somewhere; the key is to get it out of the code, to avoid recompiling and redeploying for such a trivial change.
Some good options are to list these value in an XML config file, or better yet, your database.
You'll probably want to fill out a dictionary with this data, whatever the source. This will:
Make it easy to cache
Make for clean, fast code
When the time comes to pull your data out of configuration into code, you'd add items to the dictionary like so:
Dictionary<string, IReportCreator> = configDataGetter.GetReportDataFromDB().
ToDictionary(r => r.Name, myReportCreatorFactory(r => r.ReportID))
This example assumes your getting data as entity object of some kind, and using a factory that would use a strategy pattern for your code that creates reports. There's a bagillion ways your could be doing this of course.
I assume the reports are just too extensive, varied, and different in nature that you can't just put sql and styling building block in the db?
Edit based on op's comments:
Ah, gotcha. Well, I don't know how much time you have, but as much as you push everything into some sort of factory, you have better options you'll later. I'm going to give you some thoughts that will hopefully help, from similar things I've done. Each step is an improvement in itself, but also a baby step to really separating your report logic from this shell code. Further, I can see you already know what you're doing and I'm sure know some of what I'll say below, but I don't know what you know, and it will be helpful for others.
First, pull out any and every bit of information from code to db (if you haven't already), and you'll add more db fields (and a table or two) as you improve your setup.
You might know about it already, but I'll mention it for others, to check out the strategy pattern I reference above. You can have the custom logic of each "report function" actually be in the constructor of your various strategy classes. They would all inherit from your base ReportGenerator (or sport a common IReportGenerator interface). They can and should share the same constructor; varying report parameters would be handled by a parameter of type dictionary. Each class's constructor implementation would know the types of the variables is needs (from db configuration), and would cast/use them accordingly.
Next step might be to really get rid of your select statement in your factory, using reflection. You'd have to have the name of the class as part of your reports configuration data in the db (and have a common constructor).
At this point, the way to add a new report is pretty clean, even though you've got to add a new class each time. That good. It fulfills the single responsibility and open-closed principals.
Now, there's just the final step of removing the classes from your app, so they can be added/edited on the fly. Check out MEF. This is what it's made for. Some things you might find on the internet that you probably shouldn't use are CodeDom (great when there was nothing else, but MEF is better) and the compilation-as-a-service features coming in .NET 5. MEF is the way to go.
Assuming that all reports implement IReport, you can do it using Func<IReport>, like this:
IDictionary<string,Func<IReport>> dictToReport = new Dictionary {
{"ReportA", () => CreateReportAReport("ReportA's Title") }
, {"ReportB", () => CreateReportBReport("ReportB's Title") }
, ...
};
You can then replace the switch with this code:
var myReport = dictToReport[Request.QueryString["Report"]]();
I think is better re-design this code and convert it into some database table ("Reports") to keep there the list of reports and ID of each report.
That's it.
To do this with a Dictionary<string, string> you would simply build one up as a static cache in the containing type
public class Container {
private static Dictionary<string, Func<Report>> ReportMap =
new Dictionary<string, Func<Report>>();
static Container() {
ReportMap["ReportA"] = () => CreateReportAReport("ReportA's Title");
ReportMap["ReportB"] = () => CreateReportBReport("ReportB's Title");
// etc ...
}
}
Now that the map is built you simply do a lookup in the function instead of a switch
Func<Report> func;
if (!ReportMap.TryGetValue(Request.QueryString["Report"), out func)) {
// Handle it not being present
throw new Exception(..);
}
Report report = func();
Related
How do i do this the proper way legit code. like if it do a linq query within using and the result is i want it to use on another different bracket of using another call of linq query
if i store it i could declare a pre define var neither can i use a class constructor method.
what is the proper way to do this that i may able to use it on maybe different modules or different function / method without again doing the same call over in every method.
Hope i made it clear what i want.
var globalstorage;
using (Si360DbContext _si360DbContext = new Si360DbContext())
{
var selectedItems = _si360DbContext.SaleDumpDetails
.Where(sd => sd.SaleID == saleid)
.Select(i => i.SaleItemID).ToList();
//Store data..
globalstorage = selectedItems;
}
// able to reuse it else where having the same data stored on it.
globalstorage
It depends... as always...
If you're working on a web project, some mechanism that allows you to cache would be approprate. A MemoryCache for example could be a good and fast solution. However... If the amount of data grows, or you run multiple instances of the same website for example, you may need a distributed cache system like Redis.
For different types of apps, console or maybe Windows desktop you could just create a public static variable and you're good to go. So again, it totally depends on the needs of your solution.
I have a regular C# class called "vehicle" with properties like Name, NumberPlate, MaxSpeed, etc.
All the data for the class is stored in a SQLite Database where I have a Table "Car" and "Boat". The tables colums have the same names as the class properties (however, there are more columns than class properties - vehicle is a more generic abstraction). At the moment, I have to assign the result of the query individually one by one like this:
while (await statement.StepAsync())
{
myVehicle.Name = statement.Columns["Name"];
//[...]
myVehicle.MaxSpeed = decimal.TryParse(statement.Columns["MaxSpeed"]);
}
Additionally, I have to check if some columns exist ("Car" and "Boat" have a different set of columns) which is more code than I'd like it to be.
I read about EntityFramework to map my db table to my class - but that seems overkill. My requirement is to map properties and columns that have the same name and ignore everything else.
Is there a "easy" (dev time, lines of code) way to map my table columns to my class?
Thanks for reading!
The restrictions in phone 8 mean that a lot of the standard answers to this ("just use {some ORM / micro-ORM}") won't apply, since they don't work on phone 8. You can probably use reflection for a lot of this, but: reflection can be (relatively) slow, so it depends on how much data you will be processing. If it is occasional and light: fine, reflect away.
Runtime meta-programming (the tricks used by libraries like "dapper" in full .NET to make these things really fast) is not available on restricted runtimes, so if you want to avoid lots of boiler-plate that leaves build-time meta-programming. At the simplest, I wonder if you could use something like T4 to automate creating these methods for you as C#. There are also ways to use the reflection-emit API to construct assemblies (at build-time) for phone 8, but that is a pretty hard-core route.
My thoughts:
if the amount of types here isn't huge, just write the code
if you have a lot of types, or you just feel like it, consider a build-time code-generation meta-programming step; you might even think "hmm, is this something I could make available to the community?"
of course, the first thing to do is to check that such a thing doesn't already exist
There is a little helper which might fit your case. Basically, it will take a dictionary and try it's best to populate a objects properties using reflection. I didn't try it by myself though.
You'd simply do something like:
while (await statement.StepAsync())
{
myVehicle = DictionaryToObject<Car>(statement.Columns);
}
It might need some further work to get it running but maybe a good start.
I am in the process of prototyping an implementation of a rules engine to help us with our ordering portals. For example giving discounts on items or requiring approval if certain items are ordered. We would also like to be able to add rules for dollar amounts, user hierarchy positions, and be apply it one client or more.
I feel that WWF is a good answer to this need.
All of that said however I am having a little difficulty figuring out how best to set up some of the more complex rules. I have a "condition" that I feel is best described in a LINQ query, like so:
var y = from ol in currentOrder.OrderLines where ol.ItemCode == "MYITEMCODE" select ol;
I am not against using a different framework for a rules engine or adding additional properties/methods to our objects (ex: OrderHasItem(ItemCode), etc) to make these rules more simplified but I would like to avoid having to do that. It feels self-defeating in that it forces us down the road of potentially requiring code changes for new rules.
Yes, you can use Linq queries with Workflow. In WF what you are referring to as a rule is an expression that is evaluated at runtime. Your query is selecting a subset of the orderliness based on a criteria.
For example, if I have a collection of names and I want to see only names that begin with 'R'. I could write the following code.
private static void ShowQueryWithCode(IEnumerable<string> names)
{
Console.WriteLine("LINQ Query in Code - show names that start with 'R'");
// Assuming there are no null entries in the names collection
var query = from name in names where name.StartsWith("R") select name;
// This is the same thing as
// var query = names.Where(name => name.StartsWith("R"));
foreach (var name in query)
{
Console.WriteLine(name);
}
Console.WriteLine();
}
To do the same with Workflow
Step 1: Create a Workflow with an In Argument of type IEnumerable
Here you can see that I've added the in argument
Step 2: Add a Variable for the query of type IEnumerable
Before you can add a variable you need to include an activity which has variables. In this workflow I've added a sequence.
Step 3: Assign the query the LINQ expression you want to use
You can use a method chain or query syntax.
Step 4: Iterate over the collection
In the completed workflow I used a ForEach activity to iterate the list of names and write them to the console.
This example uses C# in .NET 4.5 but the same technique can be used with Visual Basic.
You can download the sample code here
WF is a workflow engine. It's used to run factories and banks. The rule engine is just a small part of it. To make sense, any normal WF project requires a dedicated team of professionals to build it. Seems like an overkill for your specific purpose. You are very likely to bury yourself and your project in a typical fight between requirements and real skills of your team.
The use of any available .NET engine would be more justified in your situation. Keep in mind that building a custom rule engine is not an easy tasks, no matter how simple it seems from the beginning. Setting property values of a class (typically called a "fact" or "source" object) or executing actions (invoking class' methods) is what rules engines do best. And it seems that it's exactly what you need. Check out some available .NET engines. They are inexpensive, if not free, and reliable.
For a utility I'm working on, the client would like to be able to generate graphic reports on the data that has been collected. I can already generate a couple canned graphs (using ZedGraph, which is a very nice library); however, the utility would be much more flexible if the graphs were more programmable or configurable by the end-user.
TLDR version
I want users to be able to use something like SQL to safely extract and select data from a List of objects that I provide and can describe. What free tools or libraries will help me accomplish this?
Full version
I've given thought to using IronPython, IronRuby, and LuaInterface, but frankly they're all a bit overpowered for what I want to do. My classes are fairly simple, along the lines of:
class Person:
string Name;
int HeightInCm;
DateTime BirthDate;
Weight[] WeighIns;
class Weight:
int WeightInKg;
DateTime Date;
Person Owner;
(exact classes have been changed to protect the innocent).
To come up with the data for the graph, the user will choose whether it's a bar graph, scatter plot, etc., and then to actually obtain the data, I would like to obtain some kind of List from the user simply entering something SQL-ish along the lines of
SELECT Name, AVG(WeighIns) FROM People
SELECT WeightInKg, Owner.HeightInCm FROM Weights
And as a bonus, it would be nice if you could actually do operations as well:
SELECT WeightInKg, (Date - Owner.BirthDate) AS Age FROM Weights
The DSL doesn't have to be compliant SQL in any way; it doesn't even have to resemble SQL, but I can't think of a more efficient descriptive language for the task.
I'm fine filling in blanks; I don't expect a library to do everything for me. What I would expect to exist (but haven't been able to find in any way, shape, or form) is something like Fluent NHibernate (which I am already using in the project) where I can declare a mapping, something like
var personRequest = Request<Person>();
personRequest.Item("Name", (p => p.Name));
personRequest.Item("HeightInCm", (p => p.HeightInCm));
personRequest.Item("HeightInInches", (p => p.HeightInCm * CM_TO_INCHES));
// ...
var weightRequest = Request<Weight>();
weightRequest.Item("Owner", (w => w.Owner), personRequest); // Indicate a chain to personRequest
// ...
var people = Table<Person>("People", GetPeopleFromDatabase());
var weights = Table<Weight>("Weights", GetWeightsFromDatabase());
// ...
TryRunQuery(userInputQuery);
LINQ is so close to what I want to do, but AFAIK there's no way to sandbox it. I don't want to expose any unnecessary functionality to the end user; meaning I don't want the user to be able to send in and process:
from p in people select (p => { System.IO.File.Delete("C:\\something\\important"); return p.Name })
So does anyone know of any free .NET libraries that allow something like what I've described above? Or is there some way to sandbox LINQ? cs-script is close too, but it doesn't seem to offer sandboxing yet either. I'd be hesitant to expose the NHibernate interface either, as the user should have a read-only view of the data at this point in the usage.
I'm using C# 3.5, and pure .NET solutions would be preferred.
The bottom line is that I'm really trying to avoid writing my own parser for a subset of SQL that would only apply to this single project.
There is a way to sandbox LINQ or even C#: A sandboxed appdomain. I would recommend you look into accepting and compiling LINQ in a locked-down domain.
Regarding NHibernate, perhaps you can pass the objects into the domain without exposing NHibernate at all (I don't know how NHibernate works). If this is not possible, perhaps the connection to the database used within the sandbox can be logged in as a user who is granted only SELECT permissions.
Maybe the expressions will come handy for You.
You could provide simple entry places for:
a) what to select - user is expected to enter an expression only _ probably member and arithmetic expressions - those are subclasses of the expression class
b) how to filter the things = again only expressions are expected
c) ordering
d) joining?
Expressions don't let You do File.Delete because You operate only on precise domain objects (which probably don't have this functionality). The only thing You have to check is whether the parameters of the said expressions are of Your domain types. and Return types of said expressions are of domain types (or generic types in case of IEnumerable<> or IQuerable<>
this might prove helpful
I.E. expressions don't let You write multi-line statements.
Then You build your method chain in code
and voila.
There comes the data
I ended up using a little bit of a different approach. Instead of letting users pick arbitrary fields and make arbitrary graphs, I'm still presenting canned graphs, but I'm using Flee to let the user filter out exactly what data is used in the source of the graph. This works out nicely, because I ended up making a set of mappings from variable names to "accessors", and then using those mappings to inject variables into the user-entered filters. It ended up something like:
List<Mapping<Person>> mappings;
// ...
mappings.Add(new Mapping("Weight", p => p.Weight, "The person's weight (in pounds)"));
// ...
foreach (var m in mappings)
{
context.Variables[m.Name] = m.Accessor(p);
}
// ...
And you can even give an expression context an "owner" (think Ruby's instance_eval, where the context is executed with score of the specified object as this); then the user can even enter a filter like Weight > InputNum("The minimum weight to see"), and then they will be prompted thusly when the filter is executed, because I've defined a method InputNum in the owning class.
I feel like it was a good balance between effort involved and end result. I would recommend Flee to anyone who has a need to parse simple statements, especially if you need to extend those statements with your own variables and functions as well.
What would be the best approach to allow users to define a WHERE-like constraints on objects which are defined like this:
Collection<object[]> data
Collection<string> columnNames
where object[] is a single row.
I was thinking about dynamically creating a strong-typed wrapper and just using Dynamic LINQ but maybe there is a simpler solution?
DataSet's are not really an option since the collections are rather huge (40,000+ records) and I don't want to create DataTable and populate it every time I run a query.
What kind of queries do you need to run? If it's just equality, that's relatively easy:
public static IEnumerable<object[]> WhereEqual(
this IEnumerable<object[]> source,
Collection<string> columnNames,
string column,
object value)
{
int columnIndex = columnNames.IndexOf(column);
if (columnIndex == -1)
{
throw new ArgumentException();
}
return source.Where(row => Object.Equals(row[columnIndex], value);
}
If you need something more complicated, please give us an example of what you'd like to be able to write.
If I get your point : you'd like to support users writting the where clause externally - I mean users are real users and not developers so you seek solution for the uicontrol, code where condition bridge. I just though this because you mentioned dlinq.
So if I'm correct what you want to do is really :
give the user the ability to use column names
give the ability to describe a bool function (which will serve as where criteria)
compose the query dynamically and run
For this task let me propose : Rules from the System.Workflow.Activities.Rules namespace. For rules there're several designers available not to mention the ones shipped with Visual Studio (for the web that's another question, but there're several ones for that too).I'd start with Rules without workflow then examine examples from msdn. It's a very flexible and customizable engine.
One other thing: LINQ has connection to this problem as a function returning IQueryable can defer query execution, you can previously define a query and in another part of the code one can extend the returned queryable based on the user's condition (which then can be sticked with extension methods).
When just using object, LINQ isn't really going to help you very much... is it worth the pain? And Dynamic LINQ is certainly overkill. What is the expected way of using this? I can think of a few ways of adding basic Where operations.... but I'm not sure how helpful it would be.
How about embedding something like IronPython in your project? We use that to allow users to define their own expressions (filters and otherwise) inside a sandbox.
I'm thinking about something like this:
((col1 = "abc") or (col2 = "xyz")) and (col3 = "123")
Ultimately it would be nice to have support for LIKE operator with % wildcard.
Thank you all guys - I've finally found it. It's called NQuery and it's available from CodePlex. In its documentation there is even an example which contains a binding to my very structure - list of column names + list of object[]. Plus fully functional SQL query engine.
Just perfect.